Morning all. Was thinking of insulating attic, now prospect of high gas prices this winter has me moving forward sooner than planned. I have a vented attic (ridge & soffit), I’m planning to have roofer remove the soffit vents. Then foam the rafter bays.
Q1: Ok to leave ridge vents? Put some 1x under them to keep the foam off them?
Q2: Open vs closed cell foam? Right now I’m thinking closed cell foam just because I’m worried about moisture build-up in open cell foam over winter. I’m outside NYC.
Q3: What to do about build-up of moist internal air in attic? I have steam heat, so heating system will not eat moisture. Put a small inline fan in the wall to run continuously? This last would be the poor man’s whole house ventilation system, suggested by Taunton insulation book. Foam over electrical boxes to prevent air leaks into attic? Basement conditioning (keep moisture from rising) is on the agenda….
Edit: On Q1, I am thinking it would be advisable, if ridge vents stay, to screw 2x fire-blocking into ridge beam, to prevent stack effect in the event of a fire. Opinions? Is it a nice day where you are too?
Edited 9/8/2005 9:27 am ET by Taylor
Replies
Taylor - I'm no expert but here are my thoughts.
A1: Seems like you might want to seal the ridge vent from the outside so rain water/snow melt doesn't pool up in the ridge on top of your 1x. Though, doesn't seem like it should get in there in the first place.
A2: look at the buildingscience.com page for NYC climate. Closed cell won't allow you to see roof leaks for a long time, as I understand it.
A3: Most important of all points. I'm not sure and unvented approach works with steam heat because you are just introducing more and more moisture into the system. You need to dehumidify really well if you want to try this.
Bob, how is steam heat introducing moisture? Unless the system constantly vents steam, it should no more introduce moisture than electric baseboards or forced hot air.Andy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
I was losing water from the boiler last winter, plan to replace all steam vents before the cold season starts.But I suspect those pesky human exhalations are the major source of moisture.Looks like removing ridge vents and putting on roof caps is affordable. Removing soffit vents requires cutting ice&water, so may be better to just dump some cotton insulation on the vents and then foam over it.
Maybe I've just lived in apartments with bad/old steam radiators that don't do the job well. I'm not sure what the parts of the radiator are called but, the radiator regulator/vent/whistly-thing has a valve that's supposed to close when there's steam in the radiator. If they don't open and shut correctly (as I've had happen in previous apartments) then the rooms get a bit humid. So, essentially they do vent steam.Maybe I just had a lousy landlord...
You know more about steam heat than I do, since I've never had it. I was just asking.Andy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
I'm not sure and unvented approach works with steam heat
Shouldn't be any different than if it were under a cathedral ceiling, really. The moisture in the conditioned space needs to be dealt with in the conditioned space, not released into the attic. So, a dehumidifier is probably necessary.
Now, RayMoore would probably have a better answer on whether you leave the ceiling plane insulation in place, and add foam to the roof deck. In that latter case, the vapor barrier location would likely remain the ceiling plane, and not the roof plane. Which ought to mean that the existing vents might be ok. If the intent is to move the VB plane with the insulating plane to the roof deck, then, sure, the vents have to go--otherwise, you're open to the outside, functionally.Occupational hazard of my occupation not being around (sorry Bubba)
Well the idea is to include the attic in the envelope because the air handler and most of the ducting is there. And I think it's important *not* to insulate the attic floor because you don't want the attic getting too old and moisture condensing. I can block air flow as much as I can, but only so much you can do with walk-up attic.Clearly vents must be closed, just checking if there's anything wrong with the strategy of closing them (soffit vents) up from the inside, rather than ripping out shingles and i&w to remove soffit vents. Removing ridge vents not as hard as I thought.I will have to talk to AHJ, but I want to have a good story on moisture buildup, people are big on "letting houses breathe." Boy do these old houses ever breathe....
http://www.buildingscience.com/housesthatwork/cold/boston.htm
This is a good enough link to validate your current plan.
The ridge vent may allow rain to enter under certain windy conditions. I would remove it and add shingles at the ridge. The soffit can be sealed from the inside.
Be careful to seal properly with the foam. It is often difficult to accomplish when the framing members conceal parts of the space from view. If the applicator simply sprays foam into an unseen or partially hidden area, the foam will not seal the space. The foam often expands in front of the hidden areas and makes it impossible to fill all the areas. Application of foam is very difficult to get right. Attention to detail is imperative. Hire the best. Many are mainly focused on covering a lot of area and getting done. When they finish, it looks like it is completely covered but the hidden voids are potential problem areas.
And you definitely do not want to leave insulation installed at the ceiling plane.
Ray, thanks for the link, thought I had said that earlier but must have shut down browser before posting.If AHJ decides to count R-values, I have a problem. Code says R-49, but filling 2x6 rafter bays with open cell foam (per BS) only gives me R-15 to R-20. Even closed cell foam only gives about R-35.Just had a roofer give me a lecture on allowing attics to breathe....
Ignore the roofer. Can you spray 8" of open cell foam? R-30 should be sufficient. An architect or engineer can write a letter to get around code issues. Let me know if I can help.
Wow 8"....not really, just finished putting in running boards and wires for half of upstairs, along the edges of the rafters.... Also BS wants 10 perms, would you still have that with 8"?Studs at gable ends are 2x4....I assume no problem with closed cell there.... You can see daylight between the sheathing planks....Thanks for the offer of help....let me get back to you....not 100% committed but it's that or get off the potty....I'm going to take another look at that UBC draft in my copious free time this weekend....Could one have *some* insulation in the attic floor? I seem to recall 45* being the important thing....
4" of polyisocyanurate foam with a nail base of 7/16 OSB can be applied on top of your roof before reroofing. This is the best route to go in many ways. It can be more expensive. If you are reroofing at this time try that. Search for ACfoam panels.
Just had a new roof put on last year (the last one was failing). Roofer says it's good for 50 years.
Ok back from putting out fires at work, haven't given up on this idea *yet*.... So my issue is only have 2x6 rafters, so not enough room for sufficient open cell foam (8") to reach say R-30 in attic insulation....
One obvious approach is to sister 2x10s to the 2x6 rafters. Besides the fact that this is a lot of work, I also worry about (a) load on the 2x6 rafters (esp if AHJ requires DW on top of that) and (b) thermal bridging with sistered rafters (though now the 2x6 would be buried in the foam).
Thinking how to do this without sistering, I think this is relevant part of code (at least this is what was proposed a while back):
R806.4 Conditioned attic assemblies: Unvented conditioned attic assemblies (spaces between the ceiling joists of the top story and the roof rafters) are permitted under the following conditions:
1. No interior vapor retarders are installed on the ceiling side (attic floor) of the unvented attic assembly.
2. An air-impermeable insulation is applied in direct contact to the underside/interior of the structural roof deck. "Air-impermeable" shall be defined by ASTM E 283.
....
4. In zones 3 through 8 as defined in N1101.2 sufficient insulation is installed to maintain the monthly average temperature of the condensing surface above 45? F. The condensing surface is defined as either the structural roof deck or the interior surface of an air impermeable insulation applied in direct contact to the underside/interior of the structural roof deck. "Air impermeable" is quantitatively defined by ASTM E 283. For calculation purposes, an interior temperature of 68? F is assumed. The exterior temperature is assumed to be the monthly average outside temperature.
My reading is that, to ensure survival of the roof deck, there should be sufficient insulation to keep internal insulation surface at 45*. Is there a way of knowing how much open cell foam can achieve this in a heating climate?
I believe the issue of internal condensation is then orthogonal to that. It seems like one could have insulation on the attic floor and a dehumidification system to cope with condensation in the attic. Air-sealing between attic and rest of house, and removing sources of moisture e.g. from basement, would reduce load on dehumidification.
I appreciate any thoughts anyone might have on this.... Let's just say that we have natural gas (steam) heat....
You should listen to what Ray has to say on this as he's the expert, but my reading of condition 4 with foam on the roof deck should be automatically met if you remove your insulation at the ceiling plane. Then the warm side of your foam should be at the same temperature as the rest of the house (- a few degrees). If you need more R value, you can screw some polyiso, eps, or xps to warm side of your rafters (I can't remember if this was a cathedral ceiling or not) which will eliminate some of the rafter thermal bridging.My Demilec guy said he was anticipating a study shortly which would say 5" of open cell = R38 of FG. Maybe that was just salesmanship...
Actually the only reason I'm seriously considering hot roof is because of Ray's postings on the matter. I'm trying to understand why the preference for open cell, since several inches will surely mitigate the advantage of permeability.5" open cell = R-38 of FG: I think Ray is arguing that R-30 of foam is as good as R-49 of FG, which is what code requires. Unfortunately the trick is to get to R-30 of foam with 2x6 rafter bays....
Edited 9/30/2005 10:10 am ET by Taylor
I think you may be confusing water vapor permeability with water absorption. Open cell foam will absorb water (i.e. from a leak) but several inches of it has a relatively low vapor permeability.I have the same issue - 2x6 rafters and would only get about R19 filled with open cell foam. But its a quesiton of alternatives. I don't like closed cell because of leak detection and lack of flex for building movement. I could vent with 3.5" of insulation using polyiso boards which gets me in the range of R22. Not much better than R19 of foam with worse air sealing. If you look at a curve for thermal conductance (U-value :what you are trying to minimize by adding insulation) then after a certain point every inch does only a little. That's past R19, but it might help/comfort you.Look at:
http://www.uppco.com/business/BS_02.asp
How would unfaced polyiso boards (say 2") laid over the rafters work? With 5.5" of open cell foam in the bays, that would bring one to just over R-30 of foam. The boards would also provide thermal breaks. Would a leaking roof still show through the material?Of course you'll need something over the boards to protect them from UV. Probably DW. So furring strips with very long DW screws. And presumably a kneewall back from the edge of the attic. What a pain. And a bit of a load on those 2x6 rafters....
I'm not sure we are talking about the same idea. I'm suggesting something as in this link:http://www.buildingscience.com/housesthatwork/verycold/aspen.htmwith polyiso instead of the xps. You would loose leak what I'd call "instant" leak detection. But you could, every year or so or as often as you like, unscrew some of the polyiso from the underside of the rafters and take a look at the condition of the open cell foam.I'm unsure what you mean by protecting the RFBI from UV. The RFBI would be under the rafters so the roof would be protecting from UV.
They're putting XPS on the inside essentially as a VB for cold climate. Polyiso might be better for my area, warmer summers (and getting warmer...), since I believe polyiso is more permeable. That looks like a very tricky setup: ice&water on the exterior, low-perm XPS on the interior, and what happens if moisture gets between them? All they'll say is, you have to be careful. BTW any foam board would presumably be air-sealed, even if one was diligent enough to look behind it once a year (hah!), it'd be a real mess.Gable-end windows bring in sunlight, but a coat of paint would fix that. I'd prefer to get by without hanging DW from the rafters.All of these schemes require ice-and-water all the way up the roof deck. I assume that's because of fear of roof leaks. The guy who did my roof (before I knew about this stuff) says he'd refuse to put i&w over the whole roof deck. Needs to breathe, he says.Boy houses are tough.
Right, you have to air seal the whole system and build it dry. Then the only moisture entry is by diffusion and that is a very small amount. I agree it'd be a mess to look behind the foam board, but not impossible. That's really all I'm looking for - some degree of imspectability, no matter how difficult. Not all these schemes require I&W all the way, for example:
http://www.buildingscience.com/housesthatwork/cold/boston.htmthough they don't have the details on that one yet.
Well I have an alternative scheme to get 8" of foam. I don't like the idea of peeking behind the polyiso board (as if one would ever do it).My idea is to strap horizontally with 2x2s, then strap again vertically. That brings things out 3" so we can now foam 8", and it eliminates a lot of thermal bridging. Shades of the Mooney wall, except it's the roof deck and it's foam instead of cells.If you put kneewalls in (including in front of the air handler), it's not as bad as it could be. Major issue I see is getting the right depth of foam in the rafters behind the kneewall, but one could run strings as a guide.It's more weight on the rafters, but not that much I don't think.
My idea is to strap horizontally with 2x2s, then strap again vertically. That brings things out 3" so we can now foam 8", and it eliminates a lot of thermal bridging. Shades of the Mooney wall, except it's the roof deck and it's foam instead of cells.
Couldn't you just put steel drywall studs at a right angle to get the depth? It seems to me there would be very little thermal bridging and less weight, not to mention less work.
Well since Ray nixes the idea of horizontal strapping....Is your idea to have 8" "studs" coming out at right angles to the roof deck, then attach C-channel or whatever at the end after the foamers have finished spraying?One problem I see is that steel has 600 times the conductivity of wood if I recall right. I suppose there is no reason one can't do this with wood instead, and at 8" straight studs are not such an issue. Bit more of a PITA attaching strapping to the ends of the "studs."
Well since Ray nixes the idea of horizontal strapping....Is your idea to have 8" "studs" coming out at right angles to the roof deck, then attach C-channel or whatever at the end after the foamers have finished spraying?
One problem I see is that steel has 600 times the conductivity of wood if I recall right. I suppose there is no reason one can't do this with wood instead, and at 8" straight studs are not such an issue. Bit more of a PITA attaching strapping to the ends of the "studs."
No, I was just thinking of using them perpendicular to the rafters to give you some depth, and it would make spraying the foam harder - it just seemed easier than two levels of 2x.
Now that you mention it, there was a thread somewhere where they did something similar to what I think you're describing (using a 2x to come out from the rafter at 90 degrees then put 2x material between them) but that was for cellulose. I guess it would work with foam too, but you would likely have to deal with the foam that expanded too far but no big deal.
To tell you the truth, when I had the Icynene guy at my house he recommended against trying to get the higher R-value because the issue was air movement. It made sense to me.
I realize I'm knocking myself out over R-value, but I need to have a convincing story for AHJ....
I just ran across this thread when you bumped it back onto the message board.
I'd like to point out that if you are going to transform the attic space into conditioned space, there is no difference in the VB/Insulation treatment needed vs any other conditioned space, such as the living room of a chalet with a 'cathedral' ceiling.
You basically have two choices: insulate on the exterior--which means scrapping the new roofing materials you put on recently--or insulate on the interior.
(1) If you opt to insulate on the exterior and then build a new roof deck and install new roofing over all, then you need to close the existing vent system completely, and insure that the new roof deck is completely vented. This is a fairly straightforward proposition.
(2) If you choose to place the insulation on the interior, then you need to protect the existing venting from the insulation, because it is that venting that keeps the roof deck cold.
This is done by building an air-channel from soffit vent to ridge vent in each rafter bay, and placing the insulating material on the interior of that. There are some commercial polystyrene panels such as Raft-R-Mate which are designed for that purpose; however you will get a better job using 2x2's as nailers in rafter bays and nailing Ten-test or Black Joe on.
Once you have assured a clear air channel from eaves to ridge in every rafter bay, then you can add on any insulation you like: Fibreglas¯ batts, sprayed on urethane foam, rigid XPS, polyiso foam panels, whatever.
On the inside of the insulation--you being in the climate you're in--you would then add your VB--which in your case should be an aluminized mylar bubble-pack such as Reflectix¯. I say this because you are concerned about how much insulation you will get with only 2x6 rafters. You might not have realized it, but you will lose 1½" of that 5½" total to your ventilation channel. So you are effectively down to a 2x4 rafter-bay depth. That would give you R-12 with FG batts, which isn't considered much insulation for anywhere in the temperate zone.
Two things you can do are: (1) furr out the 2x6 rafters with 2x2's, getting you back to an effective rafter-bay depth of 5½ inches; and (2) add a high-reflectivity, bubble-pack vapour barrier, which alone can bump your R-factor up by quite a bit. Some products claim their ¾" thick product will provide an additional R-10 of insulation when placed as a vapour barrier.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Actually the code says the insulation should be right on the roof deck. The compelling argument I've heard for venting is preventing condensation on the roof deck in winter time. Cooling in summer I don't buy, and theoretically cooling the roof deck in winter to prevent ice dams should be accomplished with insulation to prevent interior heat reaching the roof deck. If the only reason to vent then is to remove condensation, there's no point in putting baffles in the rafters, since the interior moist air can't even reach there. You're giving up valuable insulation space for little or no purpose.At least that's how I'm reading things. Ray has actually talked me out of the baffles idea....Edit: With 2x6 joists in the attic, I'm not much interested in conditioning the space! The reasons for considering hot roof are (a) air handler and ducts running everywhere (b) walk-up attic.
Edited 9/30/2005 10:10 am ET by Taylor
I don't know what code you're working from, but it is possible you are reading a section addressing one type of situation which is not necessarily the one that applies to your house. I cannot imagine any code anywhere that prohibits insulating a roof on the inside, nor can I imagine any code requiring the insulation to be laid up directly under the roof deck so that all ventilation to the roof deck itself would be cut off.
Ventilation serves (1) to prevent condensation; and equally if not more importantly, (2) to keep the roof surface below freezing in winter so as to eliminate or reduce ice-damming at the eaves. (Some ice damming will occur anyway on south-facing roof panes. This is from solar heating on sunny winter days, but there is nothing you can do about this except to plant coniferous trees that will keep the roof in shade all day long, all year round. Which is why it's always a good idea to lay a course of EaveGard or some similar ice-and-snow membrane at the eaves.)
Warm air can absorb and hold a higher quantity of water by weight than can cold air. Condensation occurs when warm, moisture-laden air is allowed to come in contact with a cold object, which then lowers the temperature of the air and thus reduces its capacity to hold moisture. Thus to avoid condensation, you need a stream of cold, dry air continuously moving past the underside of the roof to prevent any accumulation of warm, moist air in contact with the roof.
Ventilation also serves to cool the roof in summer, whether you want to buy that argument or not. Yes, your roof may seem hotter than blazes in high summer...but without the ventilation, it would be even worse. A continually changing mass of ambient air passing across a heated object will continually absorb heat from it, thus reducing the temperature of the object. If you don't have that moving airstream, the object will continue to absorb heat from the heat source (in this case, the sun) and have nowhere to blow that heat off to except, possibly, the cold air generated by your AC unit. (And you don't want that happening, either. Not unless you're a lot richer than I am, LOL....)
Finally, the concept of a 'hot roof' seems to defy any considerations for energy economy. If you allow heat that you pay to generate inside your home to reach the roof surface, that roof surface will continually radiate away your money into the atmosphere. It's as simple as that.
If you don't want to bring the attic into the conditioned-space envelope, then your simplest solution would be to bump up the insulation in the attice floor/upper-storey ceiling. There are many ways to do this without raising the attic floor to accomodate thicker FG batts, including urethane foam and dense-pack cellulose, just to name two examples. If this is the scenario you choose, you should not close the soffit or ridge vents, as they will continue to be the only source of fresh air to keep the roof deck cold.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Dinosaur, not blowing you off. I have been skeptical of hot roofs, only recently started coming around as I read the building science. I see big problems with AC in my attic if it is outside the envelope.On a note of personal experience: When I bought my house it had FG on the rafters and gable end walls, I think it had been there since the mid-50s. The POs tore it down before we took possession, but the point is, there was no sign of any damage after it had been there for 40 years. This was even though there was a plumbing chase open down to the basement! So I'm wondering what it is these vents are supposed to save me from...Now I've got vents and a very dusty house...Certainly a hot roof is a riskier strategy, that's why I'm trying to think it all the way through.....
Well, you've got all the info; you're going to have to make the final decision by integrating it all.
Don't forget to take into account such individual variables as the way your house is sited (which way do the roof panes face); amount of direct sun on roof during the heating season (trees: decidious or conifers?, s. of the house?...); avg snowload in your area; degree-days, yadda yadda....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Taylor-
The problem with perpendicular strapping is that it makes it almost impossible to to a good job of spraying the foam. You might want to visit on of your installers jobs in progress to see what he is up against. It is harder to do than you might imagine.
Back to the framing job. Glad I don't do it for a living anymore. My house is plenty.
Oh I forgot an issue from the previous discussion: Motivation for open cell foam is detecting roof leaks from the inside. But permeability (as I understand it) depends not just on perm rating of material but also its depth. So is there a way to compute overall permeability of say 8" open cell vs 5" closed cell? If they're in the same ball park, then closed cell is clearly the way to go (if one goes that way....).
I just checked in here for the first time in a long while. I would like to respond but I don't have time right now to review all the details of this thread. I'll try to come back later and get back into it. I'm working on my own house right now while finishing up a big one at work. In my spare time, I'm doing a really fine home theatre at home. That is an area where I have a ton to learn. I've been spending alot of time over on the AVSforum.
Ray I knew you were busy, thanks for checking in. I'm still thinking about this, will post in reply to someone else on most recent thinking.BTW I currently have ceiling under air handler down. It is impossible to get access behind that thing with ductwork etc. I think if I'm going to do this it's now or never, since access behind air handler now possible from underneath.
Update: It turns out that my "new" roof is toast. I've lost the 75 yo roof deck sheathing to rot and water damage, not sure about the rafters yet.So I'm possibly in the market for the PERSIST system after all. Given my rafters and attic joists are undersized, at a minimum I need to bring in an engineer to do load calculations etc. I suspect I'll need a new structural ridge beam, possibly more rafters. And there's the whole issue of the fascia board etc. Should I look for an architect, or would an architect be overkill for this kind of project?
Should I look for an architect, or would an architect be overkill for this kind of project?
Hard to call. An engineer might not consider things like even trying to match the soffit-fascia details, just would (likely) specify the correct size rafters up from the existing top plates.
In picking either one, you'd want one familiar enough with PERSIST to give you a really good reason to yea or nay the choice. (Yet another level of complexity.)
Lastly, who ever gets picked, you'll want someone who will look at your entire house for the answer, not just the bad roof. Might be that you cound get SIPs in place if there's that much tear-out faster (always good with roofs) and not that much thicker than existing. Could be a panelized system or engineered lumber might could get you back in place and without a major dimesnion change.
Anybody who is not willing to discuss these sorts of things with you would not be my first choice to help you out.Occupational hazard of my occupation not being around (sorry Bubba)
I'm so sorry to hear this. Well, let's roll up our sleeves and get to work. This opens up all the possibilities. Do you still have my number? Give me a call and I'll see if I can help you out. I need to be reminded of the details. I'm going through a remodel at my house right now. We can be broke together. I want to see some digital pictures of the existing roof and house and eave detail.
Tell me how it is that your roof is rotten under a new roof. Did your roofer install on a damaged deck? I'm confused by this.
Ray I do not have your number, can you PL me?It looks like going with PERSIST will not be easy. I called some archies and they were pretty skeptical. I was going to talk to AHJ but might hold off a day or so until I've done more homework. The difficulty with putting PERSIST on, besides finding personnel, is that the rafters are already undersized (2x6 @ 20"oc). I expect that I might have to double up on the rafters and/or add a structural ridge beam. OTOH since some portion of the sheathing is hosed anyway, and maybe damage to at least one rafter, might as well think about biting the bullet. I haven't given up on foaming the interior (after replacing the roof again), but after this experience I'd feel much more comfortable leaving the rafters exposed.Re roof: I am guessing that water came in from gable ends between sheathing and the roof. At one end I had water leaking down on a subpanel (not live yet, thank God). At the other end, the problem has progressed much further, the sheathing is rotten and moldy. I am guessing the roofer will offer to patch it. But this is the second major failure of this 1 yo roof (we had water leaking onto our porch after the first rain, they left out step flashing....), I want my money back and get another roofer in. Who knows what other disasters are waiting to happen with this roof. This crowd BTW had the reputation of being the best roofers in the area.I will have to get pics to you later....
Instead of calling it PERSIST, refer to it as an unvented attic with cathedralized insulation. PERSIST refers to a pressure equalized rain screen and actually pertains to a wall construction, though it is generally used in conjunction with a cathedralized attic.
Architects will be just as skeptical but don't let that deter you.
Our mission is to get the HVAC system inside the conditioned space, improve indoor air quality, and improve durability.
I think the theory of steam heat with an unvented attic is okay - its just that dehumidification becomes more important. That's all I was trying to say. If you take care of the excess moisture, then it should work out - I'm just not sure how hard that is to do.
Yeah, I am starting to think that advocates of unvented attics are assuming FHA, which in winter will pull a lot of moisture out of the house air before it leaks into the attic (anyone feel free to contradict me).Taunton insulation book lays out 3 options for ventilation:
- low-cfm fan to outside basically running continuously
- rig the air handler for AC to just dehumidify, I guess add external air input
- HRVI could put a dehumidifier into the attic, have it drain to the drip pan for the air handler, but even these energy star things are pretty bad for energy consumption. Alternative is Aprilaire or one of these things, mucho dinero....
If the venting is a good thing in the summer and a bad thing in the winter, how about making some kind of hinged cover in the attic that you can open and close, much like taking down and putting up storm windows?
-- J.S.
Well I think the issue for venting is that it is critical in winter to remove moisture accumulation in the attic....Roofer says venting also cools the attic in summer but I haven't seen it..... In spring and fall, sure....
Taylor-
Wow, that is one complicated little roof line for such a small house. Can you get to all the roof deck? It would seem to be difficult to spray this one from underneath. There are many areas that appear to be difficult to get to. Applying Polyiso from above would be easier in some areas but problematic in others like under the front window and in the front valleys.
Let me change the subject. The most critical part of a house like yours from a durability standpoint is the flashings. It would be difficult to find a roofer that is competent to pull this off. It is the best investment you can make.
This seems like a house that's been added on to three or four times. The intersections of these roof lines will cause difficulties in water management, air management and thermal insulation. A comprehensive strategy is required. You need to find an angel to help pull this together. I hope you can put together a good team and funding to pull this off. I'd like to ask some questions that are raised by the pictures you posted. Call me at your convenience.