Space for insulation in roof rafters
I don’t know if this should go in construction or this forum, but I thought I’d try here. I have a completely unfinished, front gabled attic that we are going to hire a GC to renovate. In talking with the GCs about some of the options, I have heard a number of different opinions about what we should do, and they all sound pretty sure of themselves. So, I’m curious to gather some other opinions on some of the ideas we’re kicking around.
The first issue is with regard to how to insulate the sloped portion of the roof. The current status is that we have 2X6 roof rafters (actual 2X6’s the house was built in 1915) that are 20″ O.C. under a slate roof. So, we need to do two things: 1) improve the structure of the roof, and 2:) allow more space for insulation.
One of the GC’s suggested two options:
1) Sister a 2X8 to the existing rafters, and then use insulation that still allows for 1-2″ under the roof for ventilation. I didn’t like this idea, because that would only allow for R19 insulation – which doesn’t seem sufficient in the NE
2) Sister a 2X8 to the existing rafters, but have it be offset, so that the 2X8 and 2X6 only partially overlap, creating a deeper bay for insulation. I wasn’t so sure that this would be structurally that strong.
Other ideas I thought of would be:
3) Sister a 2X10 to the existing rafters (or a 2X12) to allow for more insulation [the GC thought this approach would be unweildly]
4) Furr out the 2×6 rafters with a 2X4, essentially creating a 2×10. This creates enough depth for insulation, but I don’t know about the structural integrity. My thought was they could rip 10″ widths of OSB and sister that to the 2X6 / 2X4 rafter for more structural integrity – but I don’t know if that’s really something that is done.
So, anybody have any ideas?
Just to avoid the usual boilerplate advice:
1) This is not a DIY project, we are going to hire a licensed, insured GC
2) We will be pulling a building permit
Replies
The added 2x4 is the most hokey and gives the least increase in strength.
The 2x8 in either position gives the same net strength in most circumstances. How it lands at base may vary that.
spray foam insulation is going to give you best insulation results. Closed cell gives R-7 per inch and would fit plnty in a 6" space - no venting required.
blown cellulose or BIBBs is also an otion - a good one. FG bats is your worst choice in insulation. Your odd layout size makes this a good choice too.
Another way I have done this on small jobs where space is limited is to insulate the existing spaces, then install foam panel sheets over the face of the rafters, then furr over that with strapping( furring) to hold it up and to screw the sheet rock to
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Do you just assume you need to beef up the roof structure or have you had an engineer look at it.
How steep is the pitch, how long are the rafters?
With a slate roof you don't have the same snow loads that an asphalt roof would.
Nathar,
Whatever you do, don't let a contractor install spray foam directly to the skip sheathing. You certainly don't want any spray foam on the underside of your roofing slate. The slate should last for another century, and in the future a slater may need to pull the occational slate for flashing repairs. Spray foam on the back side of the slate would make slate repair very difficult.
Martin,
You're entirely correct about skip sheathing and insulation- but I don't recall the OP saying it was skip sheathed.
Walter
Walter,
You're right. But most of the slate roofs I've seen in the Northeast are installed over skip sheathing. Even if the sheathing boards are not installed as skip sheathing, spray foam insulation can expand between knotholes and gaps between boards, contacting the back of the slates.
Edited 1/19/2008 6:44 am ET by MartinHolladay
I don't believe it's skip sheathing. The sheathing is not OSB, but planks. I believe you can occasionally see little gaps to the underside of the slate. While many people swear it's okay, I don't feel comfortable spraying foam insulation to the underside of the roof. With a baffle the only thing you lose is an inch of depth, and you should still get the same airtight seal (losing a little R-value, of course)
You shouldn't rule out spray foam. Check out buildingscience.com and some of the old threads here, it is the best insulation available. Don't just look at the R values of the insulation, those numbers are not even close to what they will get you in a real installation. Foam completely prevents air leakage, any other set up cannot unless you do a lot of other things. R 30 fiberglass, blown in, etc. is not even close to the performance of R 30 of foam. FHB and JLC have fairly recent articles on spray foam and you can probably find more in general google searches. Buildingscience.com is probably the best I've seen. The cost of energy is only going to go up, the foam will pay for itself in energy savings and the comfort level is much better than anything else.http://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climateshttp://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation
I like to sister 2x10's or 2x12's. Giving you the extra insulation space.
We install the ridge beam under the existing rafters, sister our new ones in. It flattens the ceiling a little.
A small price to pay for keeping the slate intact, and the added insulation value.
Woods favorite carpenter
Not enough information.
Is your roof sagging? Those rafters may might be more than enough.
What is the size of the room? What is the run of the roof from the sidewall to the peak?
What is the slope of the roof?
How is your headroom? Is every inch critical?
Bob's next test date: 12/10/07
The overall dimensions of the attic floorspace are about 25' wide by 45' long. The roof is about 12' tall I would say, although only about 11 1/4 feet to the underside of the roof ridge.
From what I can tell, there doesn't appear to be any kind of ridge vent at the top of the roof. So, I believe we'll need to install gable vents at either end of the attic to vent. One GC told me my state requires 4% of vent per GLA, which seems ridiculous. I'd have to have practically a whole wall of ventilation - but that's a different topic.
Looking at the structure of the existing rafters, everything looks very firm and solid. I had two GCs look at it, and both of them felt the structure looked to be in great shape. No sagging or rot anywhere. While the rafters are 2X6, they are truly 2X6, not 1 3/4 by 5 1/2.
One GC felt that sistering additional lumber to the rafters could create more problems than it would solve. He felt that we'd be adding unnecessary weight to the rafters, and that the existing rafters should be able to support drywall, insulation, and plaster. He also felt that sistering all the rafters would be a lot of time, material, and expense.
The other GC also didn't think it was structurally necessary to sister the rafters. The main reason would be for insulation, and he wanted to explore options such as high density cellulose to try and get at least R30 without sistering the rafters.
Both GCs seemed less knowledgeable about foam insulation than I am. Neither had ever really used it on a job.
To me, foam is even better for most older houses since venting is often a problem (i.e. no space for soffitt vents, no ridge vents, lack of depth on the rafters) and also the houses will have more air infiltration problems. Maybe Piffen will chime in on how long he's used it for and with older houses. I don't know the science but I've been told gable vent don't work very well at all.
I haven't heard that about gable vents, but I haven't researched it. It seems I'd have to have something up there, otherwise there'd be no real place for the air to go.
If you're going to insulate with an air space next to the roof sheathing- then have a competent slater install a ventilated ridge or use some Lomanco passive vents to gain enough ventilation.
You sound like you have a 12/12 roof. The steep slope is one reason why you aren't having a problem supporting the existing roof. The lengths of the rafters are relatively long and if you add the weight of drywall, it might be the straw that broke the camels back. One way to eliminate that possibitlity is to create a false ceiling, not attached to the roof in any way. This essentially creates two independent support systems. Headroom doesn't seem to be an issue, so every option is available regarding insulation if you go with a dual framework. If you foam, you won't need ventilation on the area foamed but you still need to be concerned if there is additional roof not foamed such as areas inaccessible below the second floor. You might not have any framing like that however. Gable vent are ineffective because they tend to create a negative and positive flow when the wind blows. They will suck snow in and pile it in the attic. They will reduce the effectiveness of eave vents because the air just shuffles back and forth at the ridge line. Bob's next test date: 12/10/07
It sounds as if you have no vents now?
Your rafter shutes require a ridge vent, rip up your slate roof to install it? You also need vents at the soffit, what is there now that will have to be punctured?
Gable vents are going to let all your conditioned air out, think open window at each end of attic.
6" is plenty for cells, way more than enough for foam.
Are you going to have knee walls, or drywall right down to the eves? Either way, the edge of your project is critical to getting it right.
Joe H
We have soffit vents now. Those soffit vents just ventilate into the attic, which is unconditioned space (currently).
There will be kneewalls, but the idea is to insulate and sheetrock all the way to eves (or enough to allow the soffit vents to ventilate into the baffles) so that we can still have conditioned space for storage behind the kneewalls. The kneewalls will also contain both a furnace and vents for forced hot air, so I want to make the area behind the kneewalls as insulated as possible.
The idea was that we would put in ceiling joists/collar ties at about 9' high, leaving some room above for ventilation. On the flat part of the ceiling, we'd have fiberglass for insulation. Unfortunately, without gable vents or a ridge vent, the air would travel up the soffits, into that unconditioned space, and have nowhere to go.
I don't see the point of it.
What is it you think you are venting? Your vent path is from the soffits to above the ceiling, you are bringing hot moist air or cold air into you attic for no good reason. You are going to create a problem, not solve it.
You would do better to insulate the entire roof area rather than leave the upper few feet unconditioned.
And why would you want to use FG on top? If you're concerned about insulation value, that is the absolute worst choice.
Joe H
Looking at the structure of the existing rafters, everything looks very firm and solid.
If that's the case, there's no reason to sister 2x10's or 2x12's.
The idea was that we would put in ceiling joists/collar ties at about 9' high, leaving some room above for ventilation.
Nail 2x4's on edge underneath the existing 2x6's up to the 9' ceiling and then nail 2x4 blocks along side the existing rafters and 2x4's. No reason to go any higher than that.
I did this on my cousins house.Joe Carola
What is that pink stuff? It looks like rigid foam with some kind of hole in it?
Those are foam baffles.
Installed from the soffitt to the ridge it gives a space for air to move underneath the sheathing.
Woods favorite carpenter
What brand/type of foam baffles? The only type I've seen look like this:
http://hardware.hardwarestore.com/27-113-roof-ventilators/curovent-foam-attic-baffle-624104.aspx
Joes picture is probably older. They look like the baffles we installed in our third spec house when I was 16. Maybe 1995-96?
Not sure what brand they are. Joe might give some more insight when he catchs up.
Woods favorite carpenter
Good Lord! How can anybody be so young? That means you were borned in about 1980! I had already been driving nails for 12 years by then! I gotta get oughta this before I get too old to
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I had been driving nails part time for a few years by then.
As a family we started building specs when I was 11, moved in each new one with bare stud walls. Finished them as we went.
Lived in them for two years and sold, moved onto building the next.
Close, born 1979. Woods favorite carpenter
2x10 or 2x12 would give you max insulation. blow cellulose. i have foam blown into my walls back in the late 70's. it has deteriatted (sp) to the point i have had to remove plastered walls to remove and replace. i know , frenchy going to give me hell, but i don't trust sight mixed foam.
The foam from back then is about two generations removed from what you can do now. The only thing i know that deteriorates todays foams is UV light and a fire that burns the place down
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I am completing a room with a ceiling like yours. I nailed some scrap 2X2 to the sides of the 2X6 just outside the top plate at the soffit. I then nailed a piece of scrap plywood to the 2X2 leaving about 1-1/4" space open on the top. I caulked the sides and bottom to create an air barrier and to keep the insulation out of the soffit. I then nailed 1' long 2X2 to the bottom and parallel to the existing roof rafters leaving 2' spaces between them. This created a thermal disconnect. To the Bottom of the 2X2 I screwed 2X4 continuously for my ceiling material. Just under the roof decking next to the 2X6 existing rafters I nailed some 1" wide 1-1/4" deep material. To that I fastened a 1" piece of Thermax and caulked all seams. This gave me an 1-1/4" continuos air channel from the soffit to the peak. I then installed ridge vent to let the air out. The reason for the Thermax was the silver facing will reflect heat in the summer lowering my need for more AC in the area and it has a very good flame rating. If the roof happened to leak this allowed the moisture to be channeled to the soffit. This left me with 8" of space under the Thermax for can lights and insulation. I am foaming that 8" which should give me an R54 for the roof system. The Thermax has a 6.5 R value and if you use FG you can attain an R38. Hope I haven't confused you. Jay
nather,
Is there any sag in your roof now? If not I'd go ahead with the 2x4's. It will also be the least expensive option.. What you want is to preserve the most area for insulation in the bay that you can..
Sistering doubles the thickness where there is solid wood.. solid wood is a lousy insulator..
Look at insulation other than fiberglas. Spray foam for example will give a slightly better insulation and make the roof a lot stiffer and quiet..
6" of dense pack cellulose = R24
2" of foamboard applied beneath the rafters = R8-10
Strapping
Drywall
You've added relatively little weight to the roof, most of which is insulation instead of non-insulative dimensional material; you've created a barrier to thermal bridging; you get R32-34 without a great loss of headroom; it doesn't require another sub.
The foam board I would be using is R-7/inch so it would only take 1-1/2" to get R-10
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I was beng conservative after accounting for thermal drift. Foil faced would give you your R-7 after stabilitzation, though.Have you ever used the soy-based foams or heard any feedback?
no I haven't on the soy based but interested when it happens.
Theoreticly it will be just fine as long as it doesn't become rat food.There have been a lot of good ideas come out in this thread. I had not considered the problem of foam in contact with slate roofing so that would need to be separated.
I do like th idea of a separated ceiling support rafter instead of sistering as long as the roof is not structurally failing now. i'm a great fan of foam and think that the criticisms I hear about it are mostly unwarranted - other than the great cost.
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If the slates have felt under them, i don't see the issue with the foam. What am i missing? And considering it's board decking, it seems that it would go a long way toward stiffening the roof structure. $$$, though...
Edited 1/20/2008 4:43 pm by splintergroupie
You said: "i'm a great fan of foam and think that the criticisms I hear about it are mostly unwarranted - other than the great cost."
There is more than merely $ cost to a building material - there is also the environmental cost. Petrochemical foams are pure energy used to save energy, so they place a considerable energy liability into our homes which requires a significant pay-down period before any real energy savings occur.
A 2000 sf house insulated with foam can contain 17,000 therms more than a conventionally insulated house. That's roughly the equivalent of 17,000 gallons of fuel oil.
Not sure what you arre saying with that. It is just plain rediculous to assert that it takes 17,000 gallons of fuel oil to foam a house if that is it.
I suppose you think fibreglass can be made and installed with no energy cost?
Or that cellulose insulation can happen with no investment in energy?You have to balance the cost against the savings long term. Dollars is one way of measuring that cost/savings relationship -the one that most people p[ay attention to.
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You said: "It is just plain rediculous to assert that it takes 17,000 gallons of fuel oil to foam a house if that is it. I suppose you think fibreglass can be made and installed with no energy cost? Or that cellulose insulation can happen with no investment in energy?"
Embodied energy is the totality of energy inputs into a product before its final use. These include the energy value of the material itself (all foam products are made from either natural gas or petroleum, so they use pure energy feedstocks), and the energy required to extract, fabricate, and transport the raw materials and finished products to their point of use.
Cellulose, since it's recycled paper with a small amount of borate, has an embodied energy of 750 btu/lb. Fiberglass contains 12,000 btu/lb, and foams from 30,000 to 48,000 btu/lb. For equivalent R-value, fiberglass contains 7.5 times as much embodied energy as cellulose, and foam as much as 30 times more than cellulose and 4 times as much as fiberglass.
In addition, the production of foam insulation contributes to fog, ozone depletion and global warming. Cellulose does none of that.
You're right, though, that most homeowners are only concerned about first cost and operating energy savings, and are OK about leaving the ultimate costs to our grandchildren. But this is a very shortsighted and selfish approach to building.
I'm always willing to revisit my information and i'm a research junkie, so i've been reading many of sites and studies on foil radiant barriers (RB). I read merchants, studies they linked to, and studies that looked less partisan. The lack of consensus or even majority rule is startling.
Some say dust has no bearing on the RB's perfomance while others say it renders the RB useless. Some said the direction the shiny side faces matters; others said it makes no difference. One person who'd installed his DW right on top of the RB said it was obvious where the paper behind his drywall stopped and the foil began. One site said the foil 'chips' were The Answer; another site said they were bogus.
One Texas A&M study said it is best placed on top of the *studs* on top of the insulation in an attic. Nevermind the nomenclature, one must question where the vapor goes, unless the authors figure the extremely high chance of the RB being damaged will provide for vapor escape. Other sites said just under the roof. Most sites addressed cooling-climate installations bec they couldn't make as good a case for using it in a heating climate where the OP dwells.
In no case did i find anyone arguing that including a RB was a cost-effective installation over insulation. Even reports linked from merchants made no claims to this. My rough calculations gave me a price of $.10/sf for the RB alone, and $.70/sf to dense-pack the OP's rafter bays with cellulose.
One person noted that radio reception was ruined by having a foil layer around the room. One wonders what it does for cell phones.
In regard to the environment, i'd be happier thinking my rafters were full of old phone books and Victoria Secret catalogs than aluminum imports.
http://www1.eere.energy.gov/industry/aluminum/profile.html
Production and Supply
The aluminum industry's raw material and product markets are global. The global primary aluminum production has been growing at a rate of 3.6 percent annually between 1993 and 2003. Domestic primary production has declined at an annual rate of 2.3 percent, while domestic secondary recovery declined at an annual rate of 0.4 percent over the same time frame. Aluminum imports continue to rise, as they have increased at an annual rate of 4.8 percent.
Thanks for providing the incentive for me to look this up.
I can step out on my porch or into th e driveway and get moderately good cell reception that does not exist in the house with foil on face of rafters and a steel roof in a 8" log home. AM radio is likewise terrible
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Look, i exercised considerable restraint with the tin-foil hat jokes, but now you're just waving a red flag...Edit: smilie face!
Edited 1/20/2008 8:50 pm by splintergroupie
I'll take the fifth....
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Splinter,
If you understand the function and mechanism of a radiant (or low emissivity) barrier, then you don't need to rely on contradictory claims and reports.
And the cost-effectiveness of a foil-faced air gap as a thermal/radiant break compared to a foam board thermal break is what needs to be considered. The foam board is certainly more costly than foil and strapping, and will offer greater R-value. But unless the foam is foil-faced and strapped, it will offer no radiant barrier. Having a radiant (low E) barrier in a wall or ceiling has a similar effect as using LowE glazing.
A double glazed window will draw the heat out of your body when standing next to it on a cold dark night. A similar window with LowE coating will reflect your body heat back and feel warm. Similarly, any surface less than skin temperature (91.4°F) will cause a radiant heat loss from the body, unless there is a radiant barrier (low E air space or reflective surface).
Foil has extremely low emissivity (high reflectivity) unless it is covered with dust or other contaminants. Low E air spaces are more effective when heat is moving downward (as in a floor) than upward or horizontally, and in slanted roofs they are more effective when heat is moving downwards (as in cooling seasons) than upwards (as in heating seasons), but are helpful in any climate (as long as they don't interfere with vapor movement or create a condensation surface.
The benefits of a radiant barrier includes the increased comfort of occupants, even at lower air temperatures (much as a radiant floor allows). While aluminum has high embodied energy and environmental costs, so does foam. And the amount of aluminum in a foil film is far less than the amount of petrochemicals in a layer of foam.
Low E air spaces are more effective when heat is moving downward
The direction heat is moving makes no difference. What makes the difference in effectiveness in a heating climate compared to a cooling climate is that the RB is facing a 180* roof instead of a 70* room - it's the percentage of heat reflected that matters not the direction it's flowing.
but are helpful in any climate
I never argued that a RB wasn't "helpful". I'm noting that for all the touted benefits, i see no figures to back up any claims that it's more cost efficient to invest in installing a foil layer compared to putting money into insulation, esp in a heating climate, which is where this poster lives.
I wouldn't be against installing polyiso with a foil face bec it wouldn't take any extra time, though the cost differential should be noted. However, back in Post 29 you wrote that a layer of foil provides for thermal briding and a vapor barrier. In truth, it's the perpendicular orientation of the strapping that provides a partial thermal break - the foil provides none - and the foil is a pretty flimsy and easily perfed VB, a function provided for already by the DP cels and the foam boards (assuming XPS).
While aluminum has high embodied energy and environmental costs, so does foam. And the amount of aluminum in a foil film is far less than the amount of petrochemicals in a layer of foam.
I'm not sure what you're comparing, but i'd need to see some explanation for that statement before i'd believe aluminum smelting is more environmentally sustainable than oil drilling. Columbia Falls Aluminum is to the north of me...and uses a quarter of the electricity in the entire state of MT.
"The direction heat is moving makes no difference."
Yes it does. A 3/4" air space with an average surface emissivity of 0.05 (equivalent to one foil face and one paper face) will have an R-value of 1.67 in a ceiling (heat moving up) and 3.55 in a floor (heat moving down), 2.80 in a vertical wall (heat moving laterally), 1.95 in a 12:12 roof in winter (heat moving up) and 3.27 in the summer (heat moving down).
"I'm noting that for all the touted benefits, i see no figures to back up any claims that it's more cost efficient to invest in installing a foil layer compared to putting money into insulation"
That depends on what costs you're including and what outcome you're measuring against - operating costs, comfort, "greenness". Builders foil and strapping is less expensive than foam board in dollars and significantly less expensive to the environment. If a radiant barrier increases comfort at lower air temperatures (lower thermostat setting), then it will save more in operating costs than the equivalent thickness of insulation.
"In truth, it's the perpendicular orientation of the strapping that provides a partial thermal break - the foil provides none - and the foil is a pretty flimsy and easily perfed VB"
I never claimed that foil creates a thermal break but that the radiant air space assembly does. Builders foil is no more "flimsy" than 4 or 6 mil poly and has a lower perm rating. It is also easier to properly tape at the seams than poly, which is rarely installed properly. Foam board will create a vabor barrier only if the joints are likewise taped.
"I'm not sure what you're comparing, but i'd need to see some explanation for that statement..."
The embodied energy of aluminum is approximately double that of plastic foam by weight, but since the weight of foil is a fraction of the weight of 1" of foam board, the foam has more of an energy impact on the environment. Other detrimental impacts might be difficult to compare. And if the foil is recycled, it has 1/10 the embodied energy of virgin aluminum. The only foam board with any recycled content was the Amofoam grey board, but that seems to have been discontinued.
Edited 1/21/2008 12:47 pm ET by Riversong
Riversong, since you've just registered and i haven't been able to form a picture of your actual abilities and experience, i was willing to scrutinize again my previous knowledge of RBs...and still am. Since you've provided effiiciency differentials to the hundredth place, perhaps you'd share your source with me so i could read it myself. As i noted, i found no such consensus, not even consistent 'camps' of information, which instead was all over the map.
As to your last statement, the 'embodied cost' of anything is certainly not static nd doesn't lend itself to easy comparisons as you've presented. In any case, cost must be weighed against actual benefits. One might consider the embodied cost of cow dung to be very low if one is a gardener, while another who lives downstream from a feed lot might consider it very high. Unless i see sourcing, i'm forced to consider your presentation as opinion bec it makes no sense on the face of it. I'm always willing to learn, though.
I may have just registered, but I didn't just start in the trade. I've been building super-insulated homes for more than 25 years, and I teach building science at a VT design/build school focused on sustainability.
The source for the R-values of air spaces is Charley Wing's "From the Ground Up", which is long since out of print. I got my initial training in thermal engineering from Charley, who was the founder of Cornerstones Energy-Efficient Building School of Brunswick ME.
While it's true that embodied energy data are not simple to calculate, given the range of inputs for every manufactured material, it is NOT a subjective assessment of impact as your statement seems to suggest. It is a quantitative and objective measurement of total energy inputs from the ground to final use.
The total environmental impact of building materials and methods is even more difficult to assess, but it's also a quantitative measurement and not determined by subjective perspective (other than deciding which impacts to include).
OK, now i know what a Larsen truss is and how to secede without really trying. <G>
Despite being bowled over by the essays, i remain a skeptic about a 32-y.o. book (there's a copy for sale in CA for $43) offering efficiencies down to the hundredth place on a system as intricate as a roof considering i can't pry any apparent trend from my recent online sleuthery. Common sense would have shook the lint off the topic by now if RB advantages were as clear-cut as you present, nay? And if this is the guy, isn't that a piece of Dow foamboard thermally un-bridging that wall?!?!?
I'm not sure this is the thread to talk about embodied energy per se, but the topic is certainly more interesting than just calculating R-values. I would agree that the embodied costs are more-or-less objective, but the values are quite subjective.
For example, i recycled a whole house that moved 35 miles from where it was no longer wanted to my empty property. Should the cost of the move be on the ledger of the owner who wanted it simply removed any way possible, or on my ledger for buying it? Or do i get to start at zero embodied energy, or do i deserve some 'pollution credits'? Should the savings be figured at the former owner's present-day disposal costs, or at the post-WWII costs of almost-clear framing lumber logged at local mills, or what i saved not buying new lumber trucked in from Canada? I'm not looking for answers (not to the hundredth place anyway <g>), just considering complexities that are not so inconsequential.
"i remain a skeptic about a 32-y.o. book offering efficiencies down to the hundredth place on a system as intricate as a roof"
Believe it or not, the laws of physics haven't changed in 32 years. And those figures for the R-value of air spaces are not specific to any structural system, but universal to any air space with a temperature gradient.
"I would agree that the embodied costs are more-or-less objective, but the values are quite subjective."
I think you're still misunderstanding embodied ENERGY data. These figures are not based on cost (in the $ sense), but purely on the number of BTUs (or, more typically, joules) required to get the material to the place of use. This energy includes the inputs from mining, milling, fabricating, and transporting (at each stage of construction) to the place of end use (in this case to the building site).
If you moved an existing structure, or took it apart and reused the materials, then the embodied energy would be only the energy required to disassemble and move the materials or the entire unit. It's for this reason that recycled materials have relatively low embodied energy - as much as 90% less than virgin materials, depending on the remanufacturing process.
Believe it or not, the laws of physics haven't changed in 32 years.
The opposite of a believer is not a skeptic. And anyway, i'm not skeptical about the laws of physics, only the lawyers of physics.
These figures are not based on cost (in the $ sense), but purely on the number of BTUs
Embodied energy...i understand the term; i was making a play on Oscar Wilde's observation that a cynic knows the price of everything and the value of nothing. Price/cost needn't be in $$$ terms for his statement to work; it can be in joules.
The concept of 'pay-go' applied to buildings is attractive from an ecological standpoint, but there is not much consensus on your theory that buildings can be broken into BTUs. And while you could pick a POV and theoretically add the physical costs, as you suggest, this says nothing at all about qualitative aspects. I can measure the cost of my greenhouse, the cost of seed, water, approximate my sweat, and i can make an educated guess about the timing of the first fruits. There is no way at all to measure the worth of the arrival of that first tomato to my tongue.
I guess much depends on whether you start with a budget and look to get the biggest bang for it, which would give you 'the projects', or if you start with an idea and see if you can create it for the least overall cost, including capital, opportunity costs, and a few dozen other non-joule aspects.
Larsen trusses...i followed the Y/M breadcrumbs, then read the secessionist essays. And i thought i was out there... <g> It'll be interesting and challenging to have your spirulina-green input on the board.
Thanks for the referral to Charlie Wing. I haven't been seriously studious about this stuff since my Ken Kern days in CA.
Edited 1/23/2008 1:41 am by splintergroupie
"i'm not skeptical about the laws of physics, only the lawyers of physics"
If you make that "all lawyers", I'm with you.
"i was making a play on Oscar Wilde's observation that a cynic knows the price of everything and the value of nothing. Price/cost needn't be in $$$ terms for his statement to work; it can be in joules."
Ah, yes... I couldn't see the wink. And here I agree with you and Oscar completely. Which is why quantifiable measures like embodied energy and greenhouse gas contribution are useful to help the average American to understand that there are "externalities" associated with industrial activity and consumer decisions that have a profoundly negative value but not an associated cost (at least not an immediate cost), such that they are never factored into our choices.
"It'll be interesting and challenging to have your spirulina-green input on the board."
I hate spirulina, but I DO try to educate people about the full spectrum of what it means to be (or build) "green" or "sustainably", including those non-quantifiable elements of our choices and lifestyles. What board are you speaking of?
The "board" i was speaking of was this Bulletin Board. "Welcome aboard", as they say.
I applaud your efforts to educate consumers about the follow-on effect of their decisions. I get a little impatient with the Dennis Weaver types who think Reduce/Reuse/Recycle means a 10,000 SF Earthship filled with cement. I like Real World solutions for those of us who aren't rich enough to be green bec we can't fit a $30K PV system into the budget.
Towards the bottom of this page i found tonight, energy savings in actual houses, not theoretical, of a Radiant Barrier are between zero and 1% of an annual energy bill in houses located in our latitudes. If money isn't limitless, it would be smarter to spend it on warm-window blankets, don't you think?
"Bulletin Board"! That dates you. These area called "discussion forums".
As far as the article you linked to on radiant barriers - that looks only at radiant heat gain barriers in attics. I'm talking about using a narrow radiant air space (foil and strapping) as a thermal break to prevent heat loss from a finished attic or other living space.
Not only does this offer some additional R-value without the cost (environmental or financial) of foam board, but also raises the comfort level to the point where a lower thermostat setting might be possible.
Radiant air spaces facing conditioned space DO make sense in a heating climate the same way that lowE (radiant barrier) windows increase both the efficiency and comfort of a cold-climate home.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
<<That dates you.>> Yabbut, i didn't get to be this old without being tough, mean, cunning, and lucky. Consider yourself warned.... <G>If you look at Table 4 from the link i gave, it shows a remarkable drop-off in $$$ savings realized as a function of a RB installation over increasing R-values of insulation in conditioned space.One thing not mentioned is the weight, embodied cost, and thermal bridging afforded by the strapping itself that is required in your system, but not necessarily with the foam board bec the DW can be screwed right over foam if it's not too thick. 1x3s on 16" centers provide somewhere around 15-20% of the thermal bridging you'd get screwing DW directly to the rafters. You're "1/2 box beam" rafter extensions, using 1/2" sheet stock to join the top and bottom chords, would still give a third of the thermal bridging of a 2x sistered rafter, no?LowE windows are not that valid a comparison to attic insulation, unless you want to start with attic insulation values in the R-1 or R-2 range. As the tables showed, with less insulation, the RB has a larger thumb on the scale, but that drops off sharply with higher R-values.The first year i was in this house, i had a sheet of pink foam in the kitchen window (i hadn't finished making all the windows before moving in), and it was lots warmer doing dishes that it is now. View sucked, though...Now...anybody seen my cane? I've got a Gray Panther meeting to attend...
If you look at Table 4 from the link i gave, it shows a remarkable drop-off in $$$ savings realized as a function of a RB installation over increasing R-values of insulation in conditioned space.
There are no tables in the article you linked to. But, once again, and you're missing this point entirely, that article dealt only with a radiant surface in an unconditioned attic - not with radiant air spaces facing conditioned space.
1x3s on 16" centers provide somewhere around 15-20% of the thermal bridging you'd get screwing DW directly to the rafters. You're "1/2 box beam" rafter extensions, using 1/2" sheet stock to join the top and bottom chords, would still give a third of the thermal bridging of a 2x sistered rafter, no?
Yes and yes, but the other way of stating the same is that the first option reduces the thermal bridging by 85% and the second by 67% - in each case a substantial reduction. I'm not suggesting that this is the equivalent of a foam board thermal break, but that it's an inexpensive and more environmentally friendly option for those of us who are averse to installing petrochemicals in order to save petrochemicals.
LowE windows are not that valid a comparison to attic insulation
But they are a perfect analogy, since in both cases they offer a low-emissivity air space which, while offering only a small increase in R-value, affords a significant increase in occupant comfort.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
The tables were linked near the bottom of the article, where it talked about Minnesota v. Orlando apps and ducting in attics. http://www.ornl.gov/sci/roofs+walls/radiant/rb_tables.html#table4As to installing petrochemicals to save petrochemicals....Of you wish to let your evaluation of Big Oil be a factor in those 'embodied' costs, that's cool. But to be fair, then you also have to factor in the environmental and humanitarian costs of smelting Al in China, shipping it to the US, manufacturing the Al sheet including attaching it to a nasty petrochemically-derived plastic web to stabilize it, trucking it to the jobsite, then hiding 20% of it behind strapping that was likely trucked in from Canada bec of the differential in softwood supply bec of the beetle outbreak, NAFTA rulings, leasing practices to Big Lumber on Crown land, and some less-stringent environmental-oversight standards than presently apply in the US. Let's look at the microcosm of petrochemical use: i couldn't stack enough foam on my Tacoma to stop it, but i have my doubts i could [safely] haul an attic-full of strapping.I'm not a big fan of Big Oil, but to spend some to save a lot makes exquisitely good sense environmentally as well as economically. I don't think you've proved that foam is a worse way to do that compared to others. I haven't proved that it is, either, but i know how it performs compared to technology that seems to be not very well documented.As to the analogy of a wall with LowE windows, I was NOT disputing the very narrow similarity of whether a RB in either case can make the occupant more comfortable. What i addressed is that the analogy breaks down when comparing the cost v. the benefit of the two cases.
Edited 1/24/2008 7:34 pm by splintergroupie
"I'm not a big fan of Big Oil, but to spend some to save a lot makes exquisitely good sense environmentally as well as economically."
You could juggle the equation so that the balance falls on the foam board side. The factors once chooses to enter into the equation - as your post makes clear - are what determines the outcome.
I source most of my lumber from local mills, which buy their timber from local foresters who treat the woods with some modicum of respect since they live where they work. The foil I use is paper (not plastic) backed and has an aluminum coating that's perhaps 1 mil thick, using very little of a resource which has negative social and environmental costs.
When I compare that to petrochemicals for which Americans and others are shedding their precious blood and which requires a military that is bankrupting America for generations to come, then the cost-benefit equation becomes much more stark.
Bottom line: it's all a subjective choice of the lesser or least of the evils that are available to us. Life is full of compromises, and we each decide where we draw the line.
Given that fossil fuel reserves are rapidly depleting and becoming the prime contributor to global conflict, I choose to use them only where there are no other reasonable options, such as below-grade insulation, or where they're the best option, such as sealing around doors and windows and utility penetrations.
I also design and build every house to be able to breath (absorb and release moisture), as our skin must do for us to live and as our clothing must do for us to be comfortable. A house envelope is a third skin. To build a hermetically sealed house which cannot breath without artificial respiration is to design in a livability and longevity problem.
And don't tell me that foil doesn't breath - you can use perforated foil and get the same low-E property. However, I rarely use foil except when retrofitting makes it the most appropriate option.
As to the analogy of a wall with LowE windows, I was NOT disputing the very narrow similarity of whether a RB in either case can make the occupant more comfortable. What i addressed is that the analogy breaks down when comparing the cost v. the benefit of the two cases.
You have presented data ONLY of the cost-benefit analysis of a radiant film in an unconditioned attic. I'll say it a third time: that has no relevance to my discussion of a radiant air space as a thermal break. The lowE window example, however, is perfectly analogous and we all know the advantages of that simple technology.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Yep, i'm with you completely on the effects of our appetite for oil. The invasion had lots of reasons for it happening besides oil, however, and i've contended that the war, while not the rousing success it would have been if we'd taken over the fields w/o resistance, has been a nice little money-maker for those who profit by such things. The end of oil might not be as bad as all that anyway...except for those who haven't adapted. Kinda like the economic meltdown...those of us free of debt and sitting on savings are a little disappointed in the actions of the Fed to lower interest rates. Boo, hiss! Bring on the double-digit inflation! Similarly, those sitting in well-insulated houses will be fine when the last oily teardrop falls.This is "Woodshed Tavern" material, however, and you should ask the Sysop for access. It's the secret folder where we sling excrement on each other for recycling jokes, voting improperly, and pretending we are better than those who find themselves in the headlines. It'd be great to argue you about global warming bec i'm pretty convinced humans can't do anything about it and no one's talked me out of that, while you are seemingly optimistic. I think we should take care of things and not waste stuff bec it's noble, but i just don't have any expectations of success when that little war is wasting enough extra petrochemicals to run Switzerland.You're just wrong about the attic and the windows. <G>Tough crowd, eh?
Edited 1/25/2008 12:39 am by splintergroupie
Yep, i'm with you completely on the effects of our appetite for oil. The invasion had lots of reasons for it happening besides oil
The Persian Gulf - to the West - has ALWAYS been about oil, just as Vietnam was about tin, tungsten, and rubber (all "strategic" resources) - not some Soviet menace. Cheney's secret "Energy Task Force" was convened at the start of the first Bush/Cheney administration to map out US foreign policy, including a regime change in Iraq. I don't suppose those petroleum company executives who crafted the plan to create a pretext to invade and occupy Iraq were at all interested in the worlds' second largest oil reserves at a time when the entire industry was predicting the approach of Peak Oil?
This is "Woodshed Tavern" material, however, and you should ask the Sysop for access. It's the secret folder where we sling excrement on each other...
Thanks, but there's more than enough excrement slinging in these threads for my appetite.
It'd be great to argue you about global warming bec i'm pretty convinced humans can't do anything about it and no one's talked me out of that, while you are seemingly optimistic.
Optimistic? Sure, but only because I see a major die-off of the excess biomass of humanity in the offing. You and I and James Lovelock all agree that global warming has already passed the point of no return. We can attempt to mitigate it, but we can't avert it - there are too many as yet undiscovered positive feedback loops (such as the millions of tons of mammoth dung that are thawing out of the Greenland permafrost and decaying, dramatically accelerating the very global warming that caused its release).
You're just wrong about the attic and the windows. <G> Tough crowd, eh?
Tough crowd, but I know when I'm right.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
<<The Persian Gulf - to the West - has ALWAYS been about oil>>You're thinking either/or; i'm thinking 2+2=22. Add to Oil the plans the neo-cons had to ring Russia with bases in its Near Abroad, the legal transfer of taxpayer dollars into the coffers of the war industry's contributors to the politicos who then vote for more war to fund the industry, the privatization of Iraqi state-run businesses besides Oil, basing to go against Iran and/or 'protect' Saudi's western oil fields, a counter to the SCO, the consolidation of power in the executive, and a host of other rationales that made invasion 'sensible'. The Tavern was created so that we could discuss such things without mucking up people's threads with off-topic stuff. I hope you reconsider.
The Tavern was created so that we could discuss such things without mucking up people's threads with off-topic stuff. I hope you reconsider.
I'll consider. How do I gain entry? Is there a secret handshake?
Aaaargh, now I'll never get off this computer.............................................................
Post your request at this link and it'll probably be sometime tomorrow when you'll be granted access and see the Woodshed Tavern in the folders listing.
88325.318
Peace full.
Um..thanks. I thought that was what i'd posted earlier, but i flubbed it.
wring websight. where are your sources for all this
"OK, now i know what a Larsen truss is and how to secede without really trying."
If Charley Wing mentioned Larsen trusses, I'm sure he didn't talk about secession. That's what we're trying to do in Vermont - return to our original status as an independent sovereign republic.
But, kidding aside, I've been using a modified Larsen truss wall system for 20 years with great success. With a 12" deep wall cavity and no thermal bridging, I can get a true R-40+ wall and easily an R-60+ ceiling (flat, of course).
The houses I've built in New England using this system require 4/5 of a cord of wood for a 1400 sf house in a 7,000 DD climate and 1-1/2 cord for a 2000 sf house in an 8500 DD zone.
But this is all off-topic.
"i remain a skeptic about a 32-y.o. book offering efficiencies down to the hundredth place"
By the way, Charley Wing's latest book, "The Visual Handbook of Building and Remodeling" is an excellent reference with loads of graphics, and it includes an abreviated version of his R-value of trapped air spaces chart.
Those "unbelievable" numbers are taken from the ASHRAE Handbook of Fundamentals.
Edited 1/22/2008 8:09 pm ET by Riversong
In regard to the environment, i'd be happier thinking "my rafters were full of old phone books and Victoria Secret catalogs than aluminum imports."Actually you wont find any phone books in your rafters. I talked to a cellulose rep at a trade show once and asked if they used phone books. He said they tried but the paper had the wrong consistency.
As for your victoria secrets catalogs if you are going to tell us where you hide them then they are not really hidden.
I blew cels in my house a few years ago and i swear there were phone books in there...with the blue-ink indexes and everything. So what do they use, if not phone books...just newspaper? Which is funny, bec newspapers have always struck me as incredibly wasteful...all those trees, all that ink...for just one day's use. Once we go all-electronic to save trees from being pulped, i wonder what a bale of cellulose will go for?
And Victoria has secrets she hasn't even told me! ;^)
Splinty, lot less blue since Wallyworld changed their bags.
Joe H
so i've been reading many of sites and studies on foil radiant barriers (RB).
You are not the only one.
The ME types who modeled one RB study were a bit redfaced when they were invited to "insulate" by applying aluminum foil as the only insulation on a test structure.
If we read the literature, that's perfect, right? Foil over an air space? Real structures can have a humbling effect upon us all.Occupational hazard of my occupation not being around (sorry Bubba)
The data says that the greatest advantage to using a RB is in a badly-insulated, well-ventilated attic compared to any other installation. That's logical, but it still begs the question of whether the money spent on RB might be more profitably invested in more insulation rather than a RB.Out here in the boonies where cable isn't an option, the interference of the metallic barrier with reception would be the killer anyway.
Cellulose, since it's recycled paper with a small amount of borate, has an embodied energy of 750 btu/lb. Fiberglass contains 12,000 btu/lb, and foams from 30,000 to 48,000 btu/lb. For equivalent R-value, fiberglass contains 7.5 times as much embodied energy as cellulose, and foam as much as 30 times more than cellulose and 4 times as much as fiberglass.
Interesting numbers, have you seen any that set those against lifecycle costs?
I've seen some competing numbers applied to FG batts based on having only a 10-15 year 'lifespan' before remodeling work sends them to the landfill. Which would double or triple the btu/lb "cost" (without factoring in the "cost" of non-degrading landfill filler).
This business gets tricky every so often, the lifespan of 'buildings' can act as a multiplier that skews results if not tempered (NPI) against other data. I've done it enough inadvertently to (occasionally) add my own grain of salt to the process.Occupational hazard of my occupation not being around (sorry Bubba)
"Interesting numbers, have you seen any that set those against lifecycle costs?"
What we DO know about life-cycle costs of insulation materials is that fiberglass gets destroyed by rodents and is non-recyclable. The fact that it's such a poor insulator (R-value decreases as temperature either drops or increases) and such a poor air/vapor barrier, would contribute to the deterioration of the building structure and the need for additional maintenance and replacement during the usable life-span of the building.
As for plastic foams, we simply don't know their longevity. What we DO know is that any environmental moisture that gets into a wall cavity framed with wood and insulated with a non-hygroscopic material like plastic foam will concentrate the moisture in the wood structure and increase the likelihood of structural damage by rot or insect infestation (foam also offers easy access for wood-boring insects).
Cellulose, because of the borate fire-retardant, is deadly to insects and, because of its hygroscopic properties, will protect wood framing from excessive moisture accumulation (cellulose can absorb 30% of its weight in water reversibly).
So any decision about insulation materials and methods should consider its impact on the life-span and life-cycle costs of the entire building assembly, as well as environmental costs from production to ultimate disposal.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
>That's roughly the equivalent of 17,000 gallons of fuel oil.
I'd be interested to see where those numbers come from. On the face of it, with oil at about $3.00 per gallon, it sounds like that would add up to $51,000 in raw material cost. Does it cost that much to insulate a 2000 sf house with foam?
Don
Last time I got a quote, it was about $15k for a 2,000 sq ft house. That number will change depending on how the house is framed, access, etc.That number he said is 100% Bulls**t. Maybe if you dropped two zero's, your at a realistic number. Maybe the insulation companies just charge 1/3 of their actual costs because they are REALLY nice people.
>That's roughly the equivalent of 17,000 gallons of fuel oil.
I'd be interested to see where those numbers come from.
DDay: "That number he said is 100% Bulls**t."
Not "100% Bulls**t", but incorrect. I did more research and rechecked my calculations. The difference in embodied energy between a 2000 sf house with blown foam and a similar house insulated with fiberglass is about 1000 therms (or roughly 1000 gallons of fuel oil).
Dense-pack cellulose with a foam board thermal break/vapor retarder is a good option, but the R-value at 3.1 pcf density is actually 3.6/inch.
However, I would be reluctant to add additional weight to the existing roof assembly without adding structural strength, and increasing the cavity depth would allow for a much better insulation level.
I would not recommend sistering the existing rafters, but instead attach 2x6s underneath them connected with 1/2" CDX glue-nailed to both to make them an integral unit without losing either insulation or ventilation space.
And I am a firm believer in venting a roof assembly wherever feasible. Roof venting is not just for eliminating vapor, but also for reducing summer heat gains and eliminating destructive ice dams.
Since you already have soffit vents, you can either cut back the ridge and add a continuous ridge vent (best option) or drop collar ties as you suggest and vent the gables. To blow dense-pack cellulose (100% recycled, low embodied energy, highly fire resistant and excellent sound attenuation), you would need a continuous vent baffle in each rafter bay (I make these with 1" nailers and mdf).
Fiberglass is a poor choice of insulation material since it is highly air-permeable, loses R-value as temperature decreases, and is a known carcinogen which often contains formaldehyde (the trigger for extreme environmental sensitivity).
Blown closed-cell urethane foam is often touted as a perfect vapor barrier, but only until dimensional changes of wood framing creates separation at joints. And, unlike a hygroscopic material like cellulose, any vapor or water penetration into the assembly will concentrate at the wood framing and accelerate damage.
I can't see an ice dam forming on a 12:12 roof. There's been a lot of discussion about running cold air up a roof, but with newer insulation products that stop the flow of moisture better, i don't find them as compelling. I know there are warranty issues with an asphalt-shingle installation, but that's not a factor here either. Your way certainly provides more room for insulation, but i still like having a thermal break, and the added insulation is offset by the room the added rafters take up, plus the cost of materials and installation. Much depends on which factor the OP places a premium on.
A thermal break could also be achieved by using 2x4s below the existing 2x6 rafters with a 1" space between, tied together with plywood to form an I-beam (or 1-sided box beam).
Another very effective thermal break which also creates a radiant barrier and vapor retarder is to staple builders' foil (paper-backed foil) on the underside of the roof framing assembly, apply horizontal strapping, and then drywall.
It's my understanding that the radiant value of the foil diminishes pretty quickly as it gets covered in dust and that it's value is not at all offset by its cost, especially in a heating climate. http://www.aceee.org/pubs/a042_s4.pdf
You said: "It's my understanding that the radiant value of the foil diminishes pretty quickly as it gets covered in dust and that it's value is not at all offset by its cost, especially in a heating climate."
That's a problem only when laying it down on top of ceiling insulation in an unconditioned attic, where dust can settle on top. For that reason, when it is used in such an attic for the purpose of reducing summer heat gains, then it should be stapled up under the rafters with the foil facing downward so that dust cannot settle on its reflective surface.
The cost of builder's foil is negligible compared to the operating cost savings it offers.
Ice does dam on steep slopes, including 12/12's. Bob's next test date: 12/10/07
Then more better insulation is in order.
Highly unlikely on a slate 12/12
If theres gutters, theres an ice dam even if it's slate. Valley's tend to create them too. More insulation will not solve the problem. Bob's next test date: 12/10/07
Jim,
You should probably stick to lecturing on that which you are more familiar with.
I've seen ice dams on every conceivable roof in MI, including metal, slate at every pitch.It would be nice to discuss matters without the condescending comments. Bob's next test date: 12/10/07
Jim,
Re read your post to me- no discussion there- you just told me how it is in your view. No asking me what my experiences have been.
You reap what you sow.
Walter
"Re read your post to me- no discussion there- you just told me how it is in your view. No asking me what my experiences have been.You reap what you sow."Exactly: I told you how it is in my view and opinion based on the facts as I understand them . I did not any make personal remark about you or challenge your personal knowledge in anyway. I did not make comments about your style of posting. Basically, I made a very short reply about the topic at hand, not about you or your experiences. If you choose to rebut them and explain further in a way that adds to the discussion...great...but if you feel the need to get personal with my simply because I have a different opinion....not great. I've seen many, many, many icecycles hanging 4' off of gutters. Those icecycles don't care what the roof materials are. When the gutters fill up and start the ice building process, the ice dam can extend upwards of 5 and 6 feet and you'd need a sledge hammer to break it up. Nothing personal. It's just what I've seen in MI after surviving 53 winters there. Bob's next test date: 12/10/07
Jim,
As my screen name suggests I work with slate roofing and have for 25+ years.
I built my home myself in 1990 with a 12/12 pitched roof on which is slate I salvaged from other roofs of houses coming down. It has built in wooden gutters lined with metal. I have never had an ice dam nor will one ever occur on this house with the ventilation I've done and the pitch of the roof.
So when you came across with a response that I felt was wrong and leaving no room for discussion by the tone of your post I said my piece.
Wasn't intended to be condescending- just tried to make you aware that others here have experience in the real world too.
Walter
I accept your olive branch. I wasn't lecturing anyone, I was just being direct and to the point. Sometimes it's better to go the slow soft way but for gawds sake, you have a big old fuzzy beard...I shouldn't have to beat around the bush with you do I? Back to the point. Even if the your house is super insulated, that doesn't mean every slate house is. Furthermore, we all know there are choke points at valleys and along side roofs that terminate in valleys. And the gutters certainly do cause ice damning if they are chock full of needles and compost. Ive seen many trees growing in them! Many in my own gutters when I lived in the woods! Conditions mean a lot when evaluating for ice dams. It's safe to say that there will be significantly less risk for ice dams on steep slopes and significantly less for slate. That I agree with. Bob's next test date: 12/10/07
Jim,
If gutters are installed properly on a slate roof- the outboard top of the gutter should be lower than the roof plane- which probably isn't always the case in the real world. That allows a snow storm to build up on the slate until it can't cling anymore- then it will slide directly off the roof.
When one of these slides happens at 2 A.M. some nite, you can be right wide awake in no time.Ask me how I know this!
I fully understand the impact valleys and dormers can have on snow retention and the formation of dams- THATS HOW I EARN MY LIVING!
Getting back to the OP though---sounded to me that might be a simple gable roof, hence my initial comment that rarely will damming occur.
With slate the cascading snow can be more problematic for some roofs than damming is--- people, cars , shrubbery etc. can be harmed by these avalanches.
In those cases snow retention might be an option to keep the snow on the roof.
http://share.shutterfly.com/action/welcome?sid=8cbsmrhq0fw¬ag=1
Walter
Some weekend inspection turned up some interesting developments.
First, our attic currently has no ventilation at all. There are no soffit vents, and there is no ridge vent. We could put in soffit vents, and ventilate behind the insulation, but then there is figuring out where the air is supposed to go. Everyone I've talked to recommends against gable vents. Too likely to bring in snow/water, and not that effective at letting out heat.
We could put in a ridge vent, but with a slate roof, that seems like a tricky and expensive proposition. Besides, what's the point? There is no air to ventilate, really.
So, the discussion now is whether to just foam the whole underside so that it is nice and airtight, and we don't need to ventilate it at all.
Any negative experiences with foam? I've seen the research, but has anyone seen any disasters with foam - particularly with a slate roof? The GC I talked to said they are doing it all the time (although I don't think they specifically said anything about slate).
Nathar, I'm glad we haven't lost you in this discussion.
"First, our attic currently has no ventilation at all. There are no soffit vents, and there is no ridge vent. We could put in soffit vents, and ventilate behind the insulation, but then there is figuring out where the air is supposed to go. Everyone I've talked to recommends against gable vents. Too likely to bring in snow/water, and not that effective at letting out heat."
Gable vents are less than ideal, but in a retrofit the ideal is often beyond reach. If you can install continuous soffit vents and baffle the rafter bays for vent space, the steepness of your roof offers a considerable "head" or height difference between inlet and outlet which will accelerate air flow. Passive ventilation should work OK. When the wind blows, there'll be variations in the airflow pattern and any roof venting system (with the possible exception of a baffled ridge vent) will allow some windblown moisture into the attic. Small amounts can be tolerated.
We could put in a ridge vent, but with a slate roof, that seems like a tricky and expensive proposition. Besides, what's the point? There is no air to ventilate, really.
A ridge vent alone is worthless without low intakes to create a thermosiphon effect.
So, the discussion now is whether to just foam the whole underside so that it is nice and airtight, and we don't need to ventilate it at all.
Careful! This is the sales pitch from every foam installer, but it's not that simple. Properly installed foam that never separates from the rafters will be an effective moisture barrier (but rafters shrink and swell and foam has been known to separate from framing). But moisture control is only one of the three functions of roof venting. The second is to minimize summer radiant heat gain (foam will only slow it down), and the third is to keep the roof surface cold in winter to prevent ice dams and the consequent structural damage (including tearing off slates).
Your roof is lightly framed and should be beefed up before adding any additional weight (insulation and drywall), so since you have to sister the rafters you may as well use the additional insulation space to ventilate and insulate with cellulose which will also reduce the flammability of the roof instead of increase it as foam would. Cellulose can absorb up to 30% of its weight in water reversibly with no deterioration in insulating quality, so small amounts of environmental water blown in through gable vents won't be a problem. Dense pack cellulose will always maintain a tight fit in the rafter bays, prevents air movement and offers better sound attenuation than almost any other insulation material. In addition, its 100% recycled and has almost no environmental impact.
One of my big concerns with dense pack cellulose is the season. I'm looking to do this in February-March, in an area where it can be pretty cold, in an unconditioned space. If the cellulose doesn't really dry out properly, I'd be in big trouble. I know they can use a moisture tester to see how dry it is, but what if there is moisture far up in the bay, or if some bays didn't dry out as well as others?
Can dense pack cellulose be used similarly to foam, i.e. without ventilation? The idea of trying to put in soffit vents and a ridge vent doesn't seem very appealing to me.
denspak cells are blown in dry - held in by a membrane of mesh stapled up - not sprayed on wet
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There's a wet-blown cellulose app, too.
I know that, but it is not called denspak
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And now the poster knows he has options! ;^)
I don't see the advantage to using mesh, though. You guys are so much more ambitious than i am...all that extra work...
Splinter,I've recently started using mesh. I find I can get a better pack with it than blowing behind a solid sheet because the mesh lets the air escape from all over the place as you blow. It is kind of a pain to put up taut and wrinkle free though. It's also useful when you just want to get insulated and won't be getting to final surfaces soon.Steve
Any trouble getting your drywall to lie down? I've popped a few Piffin screws as it is...can't see that i'd want it packed much tighter than that. I put a smaller hose, clear vinyl, on the end of the 3" hose, mostly so i could drill smaller holes in my sheathing and also to see the material flowing through. I never considered it before, but maybe that made the insulation pack tighter, too.
Hi Splinter,No trouble with the drywall yet. When you blow using the mesh it does bulge out a fair amount, but you just push it in with your hands a little bit before you hang the rock, giving it even more density. I've done quite a lot behind drywall too, and find it's actually more likely to pop screws because you are blowing into a closed box rather than a box with a cloth cover. AIr pressure builds up pretty good behind the sheet rock.BTW, mmoogie's been the handle since day one. Not hiding. Geez, how long ago was it that we all started up here? 1996? somewhere in there?Steve
Good to know about the mesh v. drywall. I'm going to be insulating my rafters in the next year, so if i can find mesh here, i'll give that a whirl. Like Mae West, i always like to try the thing i've never done before.
I've already insulated my ceiling, but i want a semi-cold room above it to be kind of a cold 'cellar' for my canned goods and the squashes 'n' taters out of the garden. Another "Mae West" endeavor...
I think you used to sign all your posts "Steve Zerby" in the old days...we grew dependent... I've been here 'only' since 2000, long after you guys had completed the first of the vent wars and the radiant/conductive/convective heat skirmishes. I remember marveling i could learn more in a week here than in a year on my own...even on dial-up! <G>
Ms Splint, Look at some of these for mesh. It comes in smaller widths, which may work for you to cut down the shipping. Although UPS will bring the 8' rolls.
http://www.sfproducts.com/Netting.htm
http://www.insulationsolutions.com/products.html
http://store.contractor-pro.com/
http://www.jrproductsinc.com/specials.html
And Regal sells direct, don't have their link though.
If you look for the cellulose manufacturers asociation you can find the closest maker and ask them who to contact locally.
Joe H
Thanks, i've bookmarked them. The Insulweb people think well of themselves, eh? About 50% more for their product, it appears. The second link had a product, aluminum trays for between rafters, that i might be able to use as a barrier between floors for radiant heat, since i don't have tubes in my basement slab. I gotta go rustle up NRTRob and see if anyone has tried that...I was looking for an insulation mesh material that was also reflective, combining both functions of a insulation mesh and a radiant barrier in one installation. Now THAT would make sense! I didn't see one, though.
Something like that here, but these people also claime their foil/foam stuff is an effective underslab insulation so don't know if I'd believe them on amything.
http://www.insulationsolutions.com/products.html
Insulweb is like Pelon, that white stuff you sew into clothes to stiffen like lapels. Those other sites have the equivilant cheaper.
Joe H
It tooks some sleuthery, but i found a price on the poly-woven foil (Radient Shield™) on that site: about $.12/sf. The mesh by itself is about $.04/sf. Might not be a bad idear....I wonder what i could get done in a day if i didn't get so wound up with these science projects... <G>
They have some rafter chutes too with reflective coating.
If I didn't sit watching the snow going sideways all day I could get something done.
Joe H
The link:http://www.regalind.com/regal_wall.htm
The MSDS for brand Regal says it's all newspaper, but phone books apparently get recycled still into newsprint still. I used the Cocoon brand, and they feature phone book recycling on their website:http://www.cocooninsulation.com/corporate/news_releases/press-120105.asp
I am glad to hear they have figured out a way to use them.
What this thread lacks:
Gene Leger
Gabe
Joe Fusco
Freddy Lugano
Steve Zerby
Somebody else, can't remember.
Joe H
We've got Steve. ^^^He's been traveling incognito!
I was just thinking about Fred in regards to this
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Gabe arguing with Gene about his houses heated by the occupants body odor, funny.
Last posts from Gene were about lightweight drywall. Still waiting to see a sheet of it.
Joe H
Hey Joe,Where you goin' with that gun in your hand?I'm still here. I got away from the boards for awhile. I've been lurking off and on though. One of the reason that I stopped jumping in on every re-hash of the vent wars is that I got tired of chasing it all around in the same circle. I'll leave the convincing to others.Steve
Steve, long time no see.
The OP asked how to insulate his attic, but was convinced by the Contractors he had contacted that venting was necessary.
Seems like many here still believe that too.
Nothing changes?
Joe H
Well, it was actually 2 contractors for venting and 1 against.
Yep. One of the reasons I turned into a semi-lurker was all the negativity from the old days. That and lack of time. Seems all I do is work sometimes. I spend more time in other categories than here in energy anymore.I've read this thread, but didn't see anything that I could add that would change anything. I wanted to let splinter know of my positive experiences with the mesh system when she brought it up though.I miss Gene Ledger's insight. It was always good food for thought. I can't count the number of times I've heard myself say "when I'm done, we oughta be able to heat this place with a light bulb" and thought of Gene.What's this Mooney Wall thing? Guess I'm gonna have to read that thread...Steve
"when I'm done, we oughta be able to heat this place with a light bulb"
This is off-topic, but the house I just finished building in December in north central VT WAS heated with a few quartz work lights until the P&H contractor finally hooked up the boiler.
Maximum design heat load for the 1922 sf house (at -10°) is 16,500 btu/hr.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
>>This is off-topic, but the house I just finished building in December in north central VT WAS heated with a few quartz work lights until the P&H contractor finally hooked up the boiler.
Maximum design heat load for the 1922 sf house (at -10°) is 16,500 btu/hr.
Maybe we should take this to a fresh thread, but I would love to talk with you about how you accomplished that.
Steve
New Thread:
http://forums.taunton.com/tp-breaktime/messages?msg=99930.1Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
The OP asked how to insulate his attic, but was convinced by the Contractors he had contacted that venting was necessary.
Seems like many here still believe that too. Nothing changes?
The laws of physics don't change.
Everyone who pushes hot (unvented) roofs justifies them by claiming that if moisture cannot penetrate then venting is unnecessary.
First, they're assuming that the foam they spray will never lose adhesion to rafters which are adjusting seasonally to ambient moisture, and that whatever other VB precautions installed will be perfect and remain so.
But they forget - or more likely ignore - the fact that roof venting serves three essential functions:
removes unwanted moisture
keeps the roof cool in the summer (and extends the life of the roof decking and roofing)
prevents ice dams
Since insulation only slows - but does not stop - heat transfer, any foamed cathedral ceiling will transfer unnecessary summer radiant heat into the living space.
And any roof, no matter how well insulated, with sufficient snow cover will have a temperature gradient which will allow snow melt at the roof surface under the right conditions, which will create ice dams if there's any substantial cold eave, with the possibility of water damage to the structure or finishes.
So let's hope that the one thing that never changes is common sense.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Hi Riversong,Welcome to the boards. Your posts are very thoughtful. But you aren't saying anything that hasn't been batted around in circles a thousand times here in the past. Don't take that as a slam or anything. I'm glad that you have the energy to o it. It's a discussion that probably needs to be had over and over again.May I ask you a few things?Have you seen recent (say in the last 10 years or so) closed-cell polyurethane foam installs where the framing has pulled away from the foam? If so have you got any photos you can post? That stuff clings so tenaciously in my experience that It's hard for me to imagine it doing that. But I have also opened walls and seen the foam efforts of the seventies that were all cracked and crumbly and pulled away from everything.re: radiant heat transfer. It's my understanding that radiant heat transfer will occur across an air gap (an hence, a vent channel). Isn't that the nature of radiant transfer, and the claims of all the in-floor radiant folks?Also, can you tell me whether/and which different materials are better at blocking radiant transfer? Or are FG, foam and cellulose pretty much equal at blocking radiant transfer?These questions are not at all meant to be combative. I just am looking to learn.Steve
re: radiant heat transfer. It's my understanding that radiant heat transfer will occur across an air gap (an hence, a vent channel). Isn't that the nature of radiant transfer, and the claims of all the in-floor radiant folks?
You're right, but I was refering the the radiant heat of the sun on the roof, which will then be transfered through the insulation/thermal bridges by conduction and re-radiated into the living space.
Also, can you tell me whether/and which different materials are better at blocking radiant transfer? Or are FG, foam and cellulose pretty much equal at blocking radiant transfer?
Insulation materials, by themselves, only slow conduction losses and gains (1 R resists 1 btu per sf per hour), and ideally convective heat transfer as well. The only way to resist radiant heat transfer is with an air space lined with at least one low-emissivity (highly reflective) surface. But the air space, if vertical, needs to be small enough (<1") to prevent internal convective loops. Radiant air spaces are most effective if horizontal with heat moving downward, as in a floor or under a roof.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
One thing that never changes is that some #### never quit.You make three assumptions and base your arguements on those. None are always true. none would be true in this case.if sprayed with closed cell foam NO moisture wanted or unwanted would ever reach the sheathing to need to be removed. In the case of this roof assembly, it would be excedingly difficult if not impossible to add venting without destroying the roof. Keeping the roof cool will not do a thing to extend the life of slates. It is argeuable whether it is worth thinking about for extending the life of composition shingles given the tiny percentage of life differential found in testingPreventing ice damns is a fiunction and factor based on the previoius assumption of yours. You really don't have much experience with properly foamed roof assemblies if you think this is a problem. You are just arguing theory here
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Paul,
You're guilty of some of the same things you accuse Riversong of. It's certainly not impossible or necessary to destroy a slate roof to install a vented ridge on an existing roof.
Yes it costs some money to complete properly, but certainly doable and helpful in certain instances.
Walter
more than just the ridge though.This place does not have soffit vents either and there are cases in these old houses where the way they were built means tht none can be added.You can note that my positions leave open other possibilities while his are firm static positions with no room to compromise which is what malkes his statements wrong. Every building is different.For instance, I said that it might not be possible to vent without destroying the roof. He claims that even with foam the roof will definitely suffer ice damns. Fact is, with good insulation, so little heat will escape that it is negligible and not enough to cause the sort of problems he contends. That only happens with too little insulation.We are all guilty of having strong opinions based on what we hear, read and know from experience. Nothing wrong with testing them against one another. If he wantss to satay stuck in what he learned thirty years ago, that's fine, but todays foams are far better than what he has set in his mind
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Paul,
It would be rare on a slate roofed house from that period that one wouldn't be able to ventilate the soffits- esp. since the attic is wide open.
I for one don't believe damming would be an issue on this roof anyway- since I thought it's a simple gable roof (please correct this impression Nathar if this isn't the case).
I'll let you other guys debate the foam issues- I know where I stand on those.
Walter
This is the question I'm most curious about:>>Have you seen recent (say in the last 10 years or so) closed-cell polyurethane foam installs where the framing has pulled away from the foam? If so have you got any photos you can post? That stuff clings so tenaciously in my experience that It's hard for me to imagine it doing that. But I have also opened walls and seen the foam efforts of the seventies that were all cracked and crumbly and pulled away from everything.Steve
"We are all guilty of having strong opinions based on what we hear, read and know from experience. Nothing wrong with testing them against one another. If he wantss to satay stuck in what he learned thirty years ago, that's fine, but todays foams are far better than what he has set in his mind."
Responding with ad hominem attacks adds nothing to your arguments.
In fact, since I teach building science and energy engineering, I keep up with the latest research in materials and methods and also rely on the unchanging laws of physics as well as decades of personal experience and the experience of countless others - such as the following from one of the leading experts in this field:
“I would not hesitate to build an unventilated cathedral ceiling in my own house. I’d have enough R-value to prevent ice damming; I’m not worried about overheating; and I’d personally make sure that the ceiling had a good air barrier and vapor retarder. But frankly, I hesitate recommending it to clients unless I’m absolutely assured of impeccable quality control. In my opinion, roof ventilation is cheap insurance against expensive callback problems. Why gamble?” <!----><!----><!---->
<!----><!---->
- J.D. Ned Nisson is president of Energy Design Associates Inc., a New York City-based building systems consulting firm, and editor of Energy Design Update.
Focus on Energy: Hot Debate Over Hot Roofs, Journal of Light Construction, June 1991
And even Joe Lsiburek, perhaps the most influential advocate of hot roofs, says that the vapor barrier must be near perfect, that indoor RH must remain below 45% and that roof venting is required above a hot roof (hybrid roof system) in extreme snow zones because of ice dam problems.
- "Understanding Attic Ventilation", Building Science Digest 102 (2006)
In addition, those who rely on plastic foam to offer a near-perfect vapor barrier over the 100+ year life span of a quality house are exhibiting an unwarranted faith in plastic. All plastics lose plasticizers over time, shrink and weaken. And any relatively non-elastic material applied against a material like wood which changes dimension seasonally with changes in temperature and relative humidity, cannot guarantee a permanent bond.
While I haven't seen evidence of foam separation, I know others who have - and I'm refering to the latest in foam insulation technology.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/24/2008 3:47 pm ET by Riversong
Edited 1/24/2008 3:49 pm ET by Riversong
Edited 1/24/2008 3:53 pm ET by Riversong
glad to see you finally presenting information that agrees with me.wouldn't it be better to simply say that SOMETIMES certain things are good or bad based on the situation instead of taking the positions you have here?
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glad to see you finally presenting information that agrees with me.
I think you mean that you are finally accepting the correctness of my answers.
wouldn't it be better to simply say that SOMETIMES certain things are good or bad based on the situation instead of taking the positions you have here?
I've taken no "positions", only presented clear and compelling arguments for certain time-tested building practices. No methodology applies in all instances, and I never made any such claim. There are instances in which spray foam makes sense and I've used it or recommended it in those cases.
I might have been a little bit cranky, but it does set me off to see somebody use a lot of big words to try and prove something that is just not true except in the most extreme cases, just because that is his pet theory.
Pet theory? I presented supporting testimony from two of the most widely recognized experts in the field, Ned Nissen and Joe Lstiburek, and instead of arguing my points you continue to stoop to personal attack.
He now says that he teaches this stiff, but I feel sorry for his students when he is just now learning that R7 foam is easy to find. The claims of cracking, separation, and old r-values tell me his information is way old and he is more stuck in his ways than I am.
My R-value numbers are the current determiniations of ASHRAE, the authority on all HVAC matters. When you're ready to return to the substance of this discussion and cease your undignified insults, then you might find that you've got something to learn from me, as hundreds of students from all over the country have already discovered.
Who knows, I might find you have something to offer as well, but not as long as you continue to demean yourself by the crudity of your remarks.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
"I've taken no "positions", only presented clear and compelling arguments for certain time-tested building practices. "There is nothing clear, compelling, or time tested about what you present. It is only your opinions and interpretations of things, much of it subjective and variable.
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Pre-coffee posting? Jays, you morning people are cranky... <G>Only thing i was considering in Nathar's case is that he said he can see the slates from the attic. I wondered if there's felt or not - no response to that. Would you chance spraying foam without a layer of paper under the slates?Slateman, what say you?
Splintie,
I've seen it done on several old roofs where the paper was disintegrated, and several where I reslated them over new doubled 30 lb. felt.
Normal spaces between sheathing boards shouldn't affect being able to repair the slate roof if foam has been used where felt is gone.
Nathar seems absent for much of this discussion.
Best, Walter
Not absent just not too much to add at this point.
"Nathar seems absent for much of this discussion."Where would you be now that the hand grenades are flying if you were the OP?;)
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I was mostly concerned about the foam possibly pushing up individual slates where the pressure escaped though a knothole or split, compared to being held down by a continuous barrier. I've never heard of spraying 9" of foam, one of Nathar's options he presented - that's a whole lot of exanding goin' on...
The foam if applied properly won't lift or remove slates if the roof is in good condition. If it's nailed with iron nails (doubtful in a house of this vintage) then it might be more problematic.
Wished he 'd post some pictures of the exterior so we could better gauge venting possibilities.
More cribbage next week- no stopping the Splinter Board !!
<<More cribbage next week- no stopping the Splinter Board !!>>After going 4 and 0 you don't have any room for improvement! <G>
The roof planks are in pretty good condtion, but certainly not airtight. There are a few places where there are cracks that you can see some kind of roof paper material, but it looks like it is rough shape. I did find one hole where I could directly see the underside of the slate.
My understanding is that polyurethane foam doesn't expand as much as icynene, is that correct? For my application, I don't think that icynene would be a good choice. If I'm going to spray directly under the roof, I don't want water going through that at all.
Here's a picture of where the rafters meet the soffit. It seems somewhat strange in that the rafters sit on two 2X4's with a space in between.
Still trying to get that picture posted
That photo didn't take
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As I thought, from what you'd said- a simple gable roof which would be straight forward to ventilate the eaves.
You might consider passive vents in the roof just below the ridge for a better job of exhausting air than a gable vent. These could be done by a competent slater at a reasonable cost. You must have someone who maintains your roof?
From seeing the picture I'm wondering if you've had issues with snow sliding off and damaging vehicles below?
Walter
Just went back and re-read some of this thread- guess you already have soffit vents in place. It's been difficult to seperate the known from the unknown here- lots of pieces of info been interjected.
I hope you'll let us know which route you'll take to insulate and ventilate once you've made up your mind.
Walter
Now you have me confused. He started out saying that he had soffit vents, but then later said that upon second look it turns out there are no soffit vents
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There are soffits. I had assumed there were soffit vents. But, actually, there are no soffit vents.
It wouldn't be impossible to put them in, just the usual difficulty and work involved in going around and putting in vents two stories up.
I might have been a little bit cranky, but it does set me off to see somebody use a lot of big words to try and prove something that is just not true except in the most extreme cases, just because that is his pet theory. He now says that he teaches this stiff, but I feel sorry for his students when he is just now learning that R7 foam is easy to find. The claims of cracking, separation, and old r-values tell me his information is way old and he is more stuck in his ways than I am
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I forgot to answer the QSince he can see the slates, I would want to investigate what exists a bit more.An easy solution to this whole thing would be a separation sheet that would add a vent passage should the owner want to add soffit and ridge vents and spray right over that.If there are large gaps in the sheathing boars and a lot of slate showing, I would fear blowing the slates off with expanding foam. That would make a separation barrier necessary. but if there were only a couple small spots where slate shows and the rest if fine, that could be dealt with by can spray before using the installera separation plane could be built in by installing foil faced foam an inch beneath the sheathing and then spraying over that. The HO would have the benefit of the vent chamber and the foil radiant barrier from heat gain in summer and the next roofer would not need to be confused about what is all this stuff oozing....
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I thought of that, but you lose that inch of insulation space. This discussion is actually very interesting in that it presents a lot of competing needs bec the roof framing is right on the cusp of needing to be beefed up for questionable benefit compared to cost. Only one person addressed the lost floor space of furring down the rafters.
Accidentally posted this in the wrong thread:
Had a chance to speak to an insulation contractor this evening to give some prices around these options.
He gave me prices of:
R38 Fiberglass with baffle - $1.40 sqare foot
R38 Cellulose with baffle - $2.50 square foot
Polyurethane (4" deep R24) - $6 square foot
Both of the first two options would require firring out the rafters with a 2X4, on end, and securing them to the rafters with a gusset plate. They would also require putting in a gable vent - he suggested putting in a powered fan with a thermometer and humidity sensor.
Now, I have about 1700 square feet of rafters that need to be insulated. So, the economics come out to be:
Fiberglass: $1,680, plus cost of gable vent
Cellulose: $3,000, plus cost of gable vent
Polyurethane: $7,200
He didn't recommend putting in more than 4" of poly foam. He said that he doesn't believe it is really necessary, that you get a really good barrier with only 4". I know technically it is only R24, but that R24 is a heck of a lot tighter than the R24 you get with other types of insulation.
I've seen the charts for efficiency and payback in walls and rofs. The foam flatens off after three inches and is really flat at 4" so there is no practical gain in effectiveness once you have four.
Don't forget to add extra framing cost to the other two.
FG batts is a waste of time IMO
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Don't forget i got you to R-38 with no extra framing AND a thermal break! Toss in the RB of foil-faced Thermax and you can roast hot dogs on reflected heat. <G>
"Don't forget i got you to R-38 with no extra framing AND a thermal break! Toss in the RB of foil-faced Thermax and you can roast hot dogs on reflected heat."
Remind me, this is a long thread and I DID forget how you got R-38 into 6" rafters.
You seem to be assuming that a barely adequate roof structure can take the extra weight of insulation and drywall - a bad gamble without an engineer's approval.
And, unless there's an air space adjacent to the foil surface, there is NO radiant barrier or reflected heat.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
#1 - I'm not your secretary. #2 - You are assuming it can't. He's got 20" centers, we don't know what species the rafters are, and your span tables are about as good as mine right now. I offered it as an option bec i think it's relevant to consider the lost floor space/headroom in these calcs about what insulation 'costs' will be.#3 - See #1.
Fiberglass: $1,680, plus cost of gable vent
Cellulose: $3,000, plus cost of gable vent
Polyurethane: $7,200
He didn't recommend putting in more than 4" of poly foam. He said that he doesn't believe it is really necessary, that you get a really good barrier with only 4". I know technically it is only R24, but that R24 is a heck of a lot tighter than the R24 you get with other types of insulation.
Foam contractors NEVER recommend putting in more than about 4" because the cost would scare away all their customers.
R-24 doesn't begin to meet current DOE standards for roof/ceiling insulation, and spray foam doesn't create a tighter envelope than cellulose with an air/vapor barrier (which could be just well-detailed drywall with vb primer). Dense pack cellulose is highly resistant to air movement, and hence vapor movement, since 99% of moisture in building envelopes comes from exfiltration and not diffusion (as determined by full-scale testing at U of Ill Building Science Dept).
Given that fiberglass performs so poorly as an insulation and is nearly useless as an air/moisture barrier, and that the urethane option is far more costly for far less insulative value ($330/R compared to cellulose at $79/R), it seems to be no contest.
And, if you want to avoid the venting, cellulose has been used successfully in hot roofs as long as air barrier detailing is thorough. In any case, I would staple strips of roofing felt between the rafters under the roof sheathing to act as a secondary membrane, since it sounds like there isn't a good membrane under the slate.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
One of the reasons I'm attracted to the foam (or at least 2" of foam) would be the opportunity to try and seal the underside of the roof from leaks. I know that's not really what it's designed for, but I would think it would have some positive effect in terms of stopping small leaks. It's not going to do much of a whole patch of slate gets knocked off, of course, but you'd think it might stop a very small hole.
You can of course create a vapor barrier right under the roof with something else, but it seems labor intensive to do - we're talking about 40 rafter bays that are 18 feet long. Seems like quite a bit of labor where a lack of attention to detail would ruin everything.
The first thing I'm waiting to hear back on is whether the rafters have to be beefed up to support the weight of drywall and insulation. If the answer is "no", then the second question is whether they would need to be beefed up if I added a 2X4 furring strip on there (and that added weight). Then I'll have a good understanding whether the added structure involved in the cellulose option is sunk cost (because it has to be done anyway) or should be added to the cellulose option.
"One of the reasons I'm attracted to the foam (or at least 2" of foam) would be the opportunity to try and seal the underside of the roof from leaks."That is the worst of reasons for considering this.You may have noticed that I think about half of Riversong's advice is cooked up out back or dug up from the mutherearth archives, but this is where one of his arfguements does have some validity and application to your situation.He has used some pretty big words to state it so you might have missed it, but if there is a leak in the roof, and you have sealed things from the inside with foam in hopes of saving a stain on the plaster, you never know about the leak until you have rotting rafters or other serious structural damages. The foam is that tight. once wood is wetted from a leak, it may not ever dry unless you live in the Sahara.
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Paul,
I was wrong about the vents- read back a ways but missed the later post that they weren't there.
I'll take issue with your post above in regards to water penetrating a foam install.
In '98 the Ice Storm Winter- just across the water from you in Castine, right close to the fort- we were slating a big house that had Cor Bond installed. It was a complicated roof and the Gc had stripped the old asphalt roof and dried it in.
If you were here that Winter you know the rains we had even before the ice hit.
I spent one whole day repairing and patching felt where bad leaks were coming thru prior to our slate going on.
I can tell you confidently that trying to expect foam on the inside to keep leakage at bay is foolhardy.
You should check out Riversongs thread on The Larsen truss, he's getting a lot of kudos over there.
My point really wasn't whether the foam will stop things from leaking in, but that they can prevent you from knowing that you have a leak, but point taken.I well remember that winter. it was wet for a good week there. My job down island was exposed to the Gulf stream temps enough that it didn't ice up but at my place ( view of Castine is just over the rise there) we had 3" to 5" of ice build, no power at all for three days and only in surges for another three days. I used the chainsaw to take ice out of my pond to keep the food in the freezer good, and hauled buckets of water out of the same holes in the ice for flushing with.I don't know about Larsen trusses. Maybe there is something for me to learn over there. Thaks for the heads up
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i was lucky- there is a dairy farm about a mile down the road so Bangor Hydro rushed to get him up and running in just a couple days and I was the beneficiary,
Lots of others around were out 10 to 14 days. Ten year anniv. Bgr. Daily has had articles lately.
I posted some measurements and structural stuff over in the construction forum, if anyone is interested.
http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=100036.1This link might help
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"Foam contractors NEVER recommend putting in more than about 4" because the cost would scare away all their customers. "not true. It is because at more than 4" the test results show decline of payback or efficiency to near zero. Also because the install is exothermic and the greater heat of a surplus thickness would impede proper curing so for a proper install, to say 6", they would need need to go twice at 3"Try to stick to facts not your assumptions and propaganda
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not true. It is because at more than 4" the test results show decline of payback or efficiency to near zero.
Decline of "efficiency"? There is a 1:1 relationship between amount of R-value in an envelope and cost savings. Twice the R-value = half the heating cost for that section. Which is why DOE recommends R-38 in a chathedral ceiling in the NE, north Central and Mountain states.
4" of urethane foam, offering an R-24 (ingoring the thermal bridging of the rafters) is hardly sufficient in these days of rapidly escalating fuel costs.
I've had foam installers admit that they don't recommend more than 4"-6" because of cost, not because they can't blow deeper.
Also because the install is exothermic and the greater heat of a surplus thickness would impede proper curing so for a proper install, to say 6", they would need need to go twice at 3"
I worked on a major renovation project a couple years ago in which the foam contractor blew at least 6" of foam in a cathedral ceiling in one pass.
Try to stick to facts not your assumptions and propaganda
You might try to heed your own advice.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
"I worked on a major renovation project a couple years ago in which the foam contractor blew at least 6" of foam in a cathedral ceiling in one pass. "You reported earlier that you have seen fracturing and cracking or shrinkage of foam instals. Now you know why. It was not installed properly. take a foam job that was sprayed that deep all at once and cut into it and you will see a lot of fracturing."I've had foam installers admit that they don't recommend more than 4"-6" because of cost, not because they can't blow deeper."Same installer who doesn't know how to do it 6" thick, no doubt. No reason to challenge the integrity of the product when the problems you see are with the installers."DOE recommends R-38 in a chathedral ceiling "DOE is a blind govt agency. They call for the same thing whether FGbatts or Denspak cells or foam jobs. You don't want to start arfguing that FG batts are as effective at the claimed R38 as foam is do you?
I am talking about actual test of actual installations in real temperature differentials that count for something. sure 6" of foam is better, but how long do you want to wait to get your payback? In the way it effects comfort and cost to heat a home in practical real life terms, 4" of R7 poly foam is plenty
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You reported earlier that you have seen fracturing and cracking or shrinkage of foam instals. Now you know why. It was not installed properly. take a foam job that was sprayed that deep all at once and cut into it and you will see a lot of fracturing.
Shame that you're so intent on proving someone wrong that you must resort to distortions and unfounded leaps of logic in order to justify your position.
I never reported that I has seen separation between framing and foam, but that it had been reported to me from a reliable person (who does building inspections and energy audits).
Nor did I make any suggestion that the 6+" cathedral ceiling job I was refering to had any defects - it did not. It was done by one of the best foam installers in VT and, other than getting excess foam on the underside of the joists and overfilling some cavities requiring significant prep before installing ceiling finish, his work was of high quality.
In fact, spray urethane loses (or never achieves) its bond to substrate if it's applied when the substrate is either too cold (resulting in condensation) or too warm (resulting in too quick a cure). It doesn't "facture" if it's too warm, it just doesn't achieve its full expansion before it cures and is more dense.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/25/2008 5:46 pm ET by Riversong
"n fact, spray urethane loses (or never achieves) its bond to substrate if it's applied when the substrate is either too cold (resulting in condensation) or too warm (resulting in too quick a cure). It doesn't "facture" if it's too warm, it just doesn't achieve its full expansion before it cures and is more dense."Like I said, it has to be installed right, just like cellulose, FG batts, or any other product. You don't put paint on a wall that is too cold and dusty either.
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"Like I said, it has to be installed right, just like cellulose, FG batts, or any other product. You don't put paint on a wall that is too cold and dusty either."
Every building material, insulation or otherwise, has to be installed correctly - that goes without saying.
But no insulation material other than spray foams are so sensitive to the temperature of the substrate. How many installers will lose a job or return another day because the roof deck is too cold or too warm? How many refuse to spray foam in the winter months because the walls are too cold? or refuse to spray a roof in the heat of summer because the deck is too hot?
As foam-insulated homes change hands and grow older, I suspect that numerous problems will begin to emerge during inspections or renovations. Plastic is NOT a long-term stable material. All plastics get brittle with time, I was told by a materials engineer who works with industry.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I've been doing some reading about soy foams. Have you any experience with that?
I've been doing some reading about soy foams. Have you any experience with that?
No first-hand experience, though I know people who've used it, often marketed as "green" foam.
I believe that the propellants are the same as those used for plastic foams and are just as toxic. And I would be concerned about another use of an important food source for non-food uses, just as the US-government-supported shift to corn-based ethanol is causing food shortages, commodity price increases, deforestation and displacement of domestic food crops for export crops.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
"the propellants are the same as those used for plastic foams and are just as toxic."Water is toxic?All the advertising info I have seen for soybased foam promotes it as non-toxic.Maybe you have a name for the toxins you imagine or some proof of what you claim.
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"How many installers will lose a job or return another day because the roof deck is too cold or too warm? How many refuse to spray foam in the winter months because the walls are too cold? or refuse to spray a roof in the heat of summer because the deck is too hot?Not sure what you mean with those rhetorial questions. My foam guys make me heat the house to be insulated and one has waited after setting up for four hours while things came up to the right temp before he started because he was not going to do it wrong. There is not any benfit in him spraying with things too cold because he gets paid by the board inch installed and a cold installation will cost him much more in materials since they will not expand properly. I'm not certin of the longevity of this but it is polyurethene which is used in high stress space exploration vehicles. It is used in the soles of shoes - and i have some worlk boots with polyurethene soles that are twenty years old that show wear but no brittleness. wood floors are finished regularly with polyurethene and it lasts just fine without going brittle. The one thing that is most damaging to it is UV, but I don't imagine too much UV will find its way into walls and arfter spaces.Your finely honed prejudices are based on the foams used in the seventies, not on any objective evidence for todays foams. They will outlast a human being. Hey - even we get brittle with time given enough of it
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I know what you mean Steve.I don't read: osb vs ply, red diamonds, truss vs rafters, sidewinder vs them overweight anchors, guards or no guards. Theres a lots more that I don't open. Bob's next test date: 12/10/07
Jim, do you read threads about BLACK DIAMONDS?
He still reads threads about insulation and venting. That never goes out of style!;)
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>>He still reads threads about insulation and venting. That never goes out of style!Heh heh. This is the first one I've read in a long time. I ignored it for quite some time till my partner pointed it out to me and mentioned that he thought he'd see me here.Nothing like a little chum in water to bring 'em out...Steve
But moisture control is only one of the three functions of roof venting. The second is to minimize summer radiant heat gain (foam will only slow it down), and the third is to keep the roof surface cold in winter to prevent ice dams and the consequent structural damage (including tearing off slates).
Yep, and in this patch of 29ºN, not one of those apply <g>
Ok, if you can get attic venting up to the maximum possible (say 1/10ach), it is possible to get a measurable difference, about 4-5º Delta-T. Locally, though, that's at the "cost" of admitting fully saturated humid air into the attic to be heated by radiation from the roof framing and deck. Venting is not always the correct answer.Occupational hazard of my occupation not being around (sorry Bubba)
"More insulation will not solve the problem"Sure it will, Jim. Heat rising through the envelope is the main cause of ice damns. Stop the heat from escaping to the backside of the roof sheathing and you stopped the ice damning.I'm with Walter, can't imagine a 12/12 slate roof having any trouble with icedams
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Piffin, I've seen ice dams on houses that weren't heated yet. Ice collects in the valleys and spreads out from there.Ice dams are especially prevalent in gutter systems. At some point in time, even on well insulated houses, the snow melts. The gutters, which often are slow runners due to accumlated debris, or slush, just start piling up the snow and ice. Sometimes, the snow slides down in avalanches and tightens up in the gutter area and creates a dense compact layer near the bottoms. The upper areas are exposed to more sunlight and melt. When the water reaches the compacted area near the eaves, it freezes solid. I've seen them 6" (probably more) thick often on any type roof. Additionally, even if the ceiling is weellllllllll insulated, it's still colder on the projected eaves, thus contributing to another reason why ice occurs in the lower regions. Lastly, when eaves and sidewalls converge, substantial accumulations occur. We all know about problem areas where sidewalls and saddles converge. Insulation is a factor, but it's not the endall. I don't suspect any roofer of any material really believes that they don't have to think about ice dam ramnifications. To do so is just an oversimplification of the discussion...unless they work in warm climates. Bob's next test date: 12/10/07
you make some good points but also some bad assumptions.For one - your point about unheated houses. they are heated, just not actively yet. They are subject to solar gain and radiant earth heat that lets the interior warm up. I was recently inside one that we had framed up quite a while earlier, and crawled up to check some work in the attic near the chimney. It was cold enough on the two main floors to feel frost and see your breathe, but it was quite comfortable right up under the roof sheathing, where the heat collects. fact is - it takes heat to make an ice damn. The snow has to melt and the water flow under the snow down to a colder edge at the eave to create the ice that damns things up.The slightest bit of that on slate leave no friction to hold the snow on the roof. Especially at 12/12.Now if you add gutters to the discussion, you have a point. One of many reasons why I consider guttered roof a bad design.I do see snow drift deep into valleys but don't consider snow an ice damn. It is just deeper snow. It still takes heat to melt and make water flow to make an ice damn."even if the ceiling is weellllllllll insulated, it's still colder on the projected eaves,"
Disagree. if the eaves are cold enough to freeze water into ice faster than it can drip off, the rest of the roof surface is cold too, unless too much heat energy is being allowed to escape through the ceilings.
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Yes it does require heat loss through the roof to create the melting that can cause an ice dam. But it's incorrect that "if the eaves are cold enough to freeze water into ice faster than it can drip off, the rest of the roof surface is cold too".
Unless there is heat loss into the soffits, then the eaves are cold. All roof systems that are not fully and adequately vented from soffit to ridge will have increased roof surface temperatures, no matter how much insulation is below them.
The key to snow melt on any roof is whether the temperature gradient is sufficient to create surface temperatures above 32°. As snow builds up on a roof (snow is an insulator), the temperature gradient shifts outward. An R-38 cathedral ceiling with 10" of snow on the roof at 25° outside temperature can cause the roof surface to rise to 34°. The snow at the roof surface will begin to melt, but the thick snowpack will prevent the rest of the snow from sliding. The snowmelt will run down to the colder eaves and freeze. Once an initial ice dam is created, then the snowpack is even less likely to slide, and eventually a reservoir of water is contained and migrates up under the roofing.
Other than temperature gradient, the most common cause of ice damming on an unvented or poorly vented roof is warm air leakage through poor detailing at interior soffits, ceiling fixtures, kneewalls, utility penetrations, rafter plates, etc.
While gutters will make an ice dam problem worse and often results in tear-down of gutters, they are not the cause of ice dams. A well-insulated and tight house with a fully vented roof will not experience ice dams. The primary preventative of ice dams is roof ventilation.
all that right except this-" but the thick snowpack will prevent the rest of the snow from sliding."It is when the snow starts to turn to water at thje surface of slate or steel that it becomes a lubricant and the snow load overcomes the friction holding it in place and slides off.You come at it from a POV of scientific jargon but I am seeing it from a POV of thirty years on roofs
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It ain't "jargon". And the same phenomenon occurs in a snowpack on a mountain: a slip plane caused by a lubricating layer (ice, dense snow, or water) allows the overburden to create a fracture line and slide. But it needs to be a sufficiently large slip plane.
The most common heat leakage spots on a ceiling/roof assembly are just above the eaves, due to poorly detailed kneewalls with leaky ductwork, or utility penetrations in or near exterior walls, or kitchen or bath soffits with can lights or fan lights. If the snow melt is only at the bottom of the roof, then there might not be a sufficient slip plane to allow the snowpack to fracture and slide.
While ice dams are less likely on a steep roof with slate roofing, they can and do occur, particularly on the north side.
I've got only 26 years in the business, but I've seen a few things too.
I am arguing from a point of the well and properly done insulation/ventilation job but you and Jim have argued against my conclusions citing examples of what happens when the insulation is poorly done.So you agree with me
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Next time i'm going to include a detail.
~Splinter, busy calculating how much snow can be held in the valley of a 12:12 poorly FG-insulated, low-heel roof w/no vapor barrier at 33 degrees ambient temperature with an improperly-installed gutter system. Oh, and it's covered in AstroTurf.
We agree, perhaps, that a well-insulated ceiling/roof assembly that's thoroughly ventilated (continuous soffit and ridge vents with baffles and unobstructed pathways) and with careful detailing and airsealing both inside and out won't have ice dam problems.
But on a number of issues, we disagree.
And my comments about ice dam problems are based on real-world building methods and real world examples, such as the one presented by the original poster.
Here they would want an engineer's certificate.
My 2 cents: increase the rafter depth with an I joist, deep enough to accommodate appropriate insulation Insulate to required R value (probably R40), strap the roof for ventilation or go solid EPS or spray. In any case you will not be able to use your present roofsystem.
Did you check to see if you could use the existing ceiling joists for floorjoists or do you have to make changes there also?
Loadbearings?
What's the slope on your roof?
I'm suspicious that you need to "improve the structure" of the roof if you have the original slate from 1915 up there. Why all of sudden NOW is the roof going to collapse?
I can see sistering joists strictly for the insulation but putting 2x10s or 2x12s will also cut down on the interior space of any room that you will end up with.
(said abit wistfully) You wouldn't happen to have a photo of the house would you? (if you say you've got acreage ONTOP of having an old house it will totally KILL me....sigh)
Add 1/4 of the upholstery on my Victorian settee. I'm counting down the days to Doggy class.
My first thought is you should be hiring an architect. They'll be able to tell you the code requirements for your area and do the calculations to make sure the roof structure is adequate. There are a number of ways to do what you have in mind. Sistering 2x10s or 2x12s is better than tacking on 2x4s from a structural point of view.Another possible tactic is to create a scissors truss.(Basically your room would have a ceiling with a shallower slope than the exterior.) Spray foam or polyisocyanurate board insulation both require fewer inches for the same R value as fiberglass.
I've got an architect and a structural engineer, actually. Just trying to avoid asking them too many dumb questions at $120/hour.
After this weekend, the structural engineer should be able to tell me whether the roof rafters need more support. The preliminary assessment is no, so the question really just comes down to insulation.
My thought was to spray 2" of closed cell foam directly under the roof to get a completely air tight seal, and then come back and use spray in place cellulose to get a pretty good R value for less money than using all foam. However, the one insulation contractor I talked to said that wouldn't be cost-effective at all. That I'd be better off just going with 6" of cc foam.
I'd like to put 1" of solid foam board over the studs and behind the sheetrock, to give me a good thermal break. Is the foil covered board for vapor barrier or for fire protection?
I am replying from the future. The spray foam, closed cell or open cell, will shrink and you will loose your supposed air tightness. In fact, if this is what you did in 2008, by the time you read this the foam will have shrunk enough to create air leaks.
Also from the future is a video from the Build Show Network where Matt Risinger has used spray foam between his garage and the main part of the house. He is trying something very different where a water soluble caulking material is sprayed into the air and the space inside is pressurized to find and seal any leaks. The material builds up where there are leaks and it is white in color making it easy to see. Guess where the biggest leaks were? Between the foam sealed areas of the garage to the main living spaces and the foam installation was less than six months old. Matt has come to the conclusion that foam is not as great as he previously thought. It turns out that the best products for sealing air leaks are carefully applied peel and stick materials that are rolled onto the surface rather than simply pressed onto the surface. Where ever he used this on his house rebuild, there was no leakage. The other material that work well are liquid flashing products.
If I were you I would get some assistance from a structural engineer. You should consider that fact that you house is 100 years old and the roof rafters haven't sagged in all this time. If all you are trying to do is increase the depth for additional insulation you may want to talk to some folks that have insulated their attics with only 4 to 6 inches of insulation.
I grew up in a house built in 1920. My parents stored many things in the attic and my father wanted to bring down the temperature in the attic during the summer. So one fall day in 1963 we insulated the attic with foil faced fiberglass bats with a 1/2 space between the bat and the upper side of the insulation. This wasn't planned for, it just worked out that way. That winter the attic was a balmy 72 F when the outside temperature was in the 20s. The following summer the attic was a comfortable 80 F. An interesting fact was the insulation between the attic and the ceiling of the second floor. There was grey paper and foil insulation that was composed of three internal pockets that ran the entire length of the radiant barrier insulation. There was a foil layer on the top facing the inner spaces of the attic. We suspected that it was originally inflated to the spacing of the ceiling rafters because it fit tightly between the rafter faces. The rafters were 2X10 (2 inches by 10 inches Douglas Fir. When we built and addition to the house for my parents new bath and bedroom we discovered that all the structural framing was Douglas Fir. It was so hard that pilot holes were necessary even when using a nail gun. Without the pilot hole the nails were crumpled against the wood.
Recent research shows that an air space of 3/8" is sufficient for free moisture movement. See this: https://www.buildingscience.com/documents/insights/bsi-038-mind-the-gap-eh
One additional thing about a slate roof is that it is not air tight. So if you had air movement in the space between the insulation and the underside of the slate and sheathing, air and moisture will penetrate the gaps in the slate and vent to the outside; no ridge vent needed.