Merry xmas to everyone- I will be building a new home for myself in the spring and I think I would like to use the two part blow in foam insulation in the walls.I can’t seem to find any info about this material, such as price, installation nor whether it would be worth the extra cost. Sure would appreciate any information on this subject, sincerely, bob
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There are a couple types.
Corbond is one brand name you can look for. they have good research info published as "Walls that work"
There is urethene foam with R values approaching 7 per inch, and another I have nort used -polyisoanurate, I think weighing in at about R5/inch.
The iso is moisture permeable but the urethene makes up a vapour bar.
You should be looking for two inches under floors and at perimeter, three in walls, and four atop.
Costs have run previously at about a buch per board foot, installed.
I definitely believe it is worth the bucks. In addition to the great insulative quality, it makes for a much quiter house, and infiltration from convection loss is all but eliminated.
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Try http://www.fomofoam.com I used the product on a job in Maryland and was very happy. Cost is about $1.00/bd ft. The installation time is very short. Make sure that you have your work area very uncluttered. The two part sets in 60 secs and if you don't keep it flowing it will set up in the nozzle. New nozzles are reusable, just drop them in a can of acetone.
thanks for the help guy, bob
Glad I could be of some insight. The factory is in Akron, OH but they ship. I put up 600 bd ft in about 3 hrs (three one hour sprays). Works great.
When you guy are talking about bdf are you talking about bdf or are you talking about square feet of stud cavity? Your cost per bdf is insane. with a 5 1/2 inche deep wall you are talking about 59 bdf per 16 inch stud cavity? ??????
There'd be no advantage to filling a 5.5" cavity with polyurethane. At R7.14/in, it'd be overkill.When we budget for foam in our houses, it's about 70 cents/bdf.
OoooooKKKKKKK,
To get R 20ish in the walls you need 3 inches of your R 7.1 foam. At your $.70 per BOARD FOOT! that is $2.10 per SQUARE FOOT of wall vs. 50 cents for FG (unfaced R-21 batts).
Are you still talking Board foot? What a weird application for bdf. But if that is the nomonclature.
Yeah, that's right. I'll take the qualities the foam brings any day over fg. If you've experienced it, you know what I mean; if you haven't, I guess it doesn't make sense. I think there's payoff, not only in energy savings, but also in the comfort of no air infiltration, in sound proofing, and in sturdiness. Typically foam is measured by the pound, but that equates to bdf pretty well at a given density. Sf of course depends on thickness, which varies by application. No stranger measuring it by bdf than measuring lumber that way. My app is here: http://www.itsa.info/Foam.shtml, so fg isn't even an option, and neither is polyicynene. But for frame, I'd want it, too.edit: and R21 fg does not measure a consistent 21. As temp drops, the effectiveness drops a lot, too. And it leaks air like a sieve.
Edited 12/16/2004 11:43 pm ET by Cloud Hidden
You say: "No stranger measuring it by bdf than measuring lumber that way."
Well lumber has a history behind bdf, nothing else that I can think of is measured that way. So, why would you measure foam that way? If you buy foam by the sheet they don't sell it by the bdf. So, whatever. Just a curious thing, in my opinion.
"R21 fg does not measure a consistent 21. As temp drops, the effectiveness drops a lot, too. And it leaks air like a sieve."
If the air is not moving, FG does not leak. If the wind blows at the house and the air is not able to move through a plastic vapor barrier there is no air through the FG. Sure not perfect, but I would not overstate the limitation of FG. As for the effectiveness as temp drops? I have heard that, not sure why? Perhaps it has something to do with your first point of air movement. If the air which is moving is a lower temp it takes more energy from the house to heat the "new" air in the tiny FG pockets. If the first point is addressed (air movement) the second point is moot. I would think.
I guess I would really have to see the figures. People spend a lot of money on stuff with no pay back. Just as an example, if you spend $3000 (50cents a sq for wall cavity) vs $2.00 a sq ft for foam that is a $9000 delta. If your opportunity cost of money is 10% you need to save $900 each year for that to pay off. I live in a 2400 sq ft house build with SHT in 1970's. I don't spend $900 each year to heat it. Pay off for the extra 9 grand???????
Like I said, foam is measured by the pound. But that doesn't allow for ready comparison, so it's equated to bdf, because sf requires thickness, and that can vary. Just an easy way to compare.And for cost comparison, PUF cost includes the cost of installation, which is about equal to the wholesale cost of the materials. Dunno if fg cost is installed cost or not.Not gonna try to talk you into it. I don't do frame houses anyway, so...
Cloud, not looking to get talked into or out of anything. I just push the discussion as to flush out all the details and facts to consider. You are correct, in that my 50 cent per sq ft for FG was just material cost. I guess, I sited that figure since I would likely do it myself. However, if I got really count on the foam being a good long term investment, then that is something I could pay someone to do.
One sad thing about home building is htat since the average stay in a house is something like five years, people don't evaluate options on a ten year or twenty or even one hundred time frame. Why put in a 90% eff furnance, why spend for foam, etc.. Not my thinking, but who can blame people?
"If the air is not moving, FG does not leak. If the wind blows at the house and the air is not able to move through a plastic vapor barrier there is no air through the FG. Sure not perfect, but I would not overstate the limitation of FG. As for the effectiveness as temp drops? I have heard that, not sure why? Perhaps it has something to do with your first point of air movement. If the air which is moving is a lower temp it takes more energy from the house to heat the "new" air in the tiny FG pockets. If the first point is addressed (air movement) the second point is moot. I would think."Your arguments are based on assumptions and not on full facts or studies. You also assume that a wall can be built so as to disallow infiltration in the real world.Let me explain...
What you are missing is the effects of rthe convection loop within a wall cavity, the same thing that happens between two pieces of glass in a window section.
The air near the outside panel of the wall is cooled and sinks to the bottom. This air displaces other air sitting there at the same time that wair warm air within the FG rises to the top of the wall cavity. What you end up with is well known and diocumented in the insulation industry as a convection loop. warmth in the interior wall panel is transfered to the air nearest it and rises to the thop and then to the outside of the covity, then sinks again to the bottom near the outside wall panel. As it does so, the warmth it contained is transfered to the outside. Thuis all happens more slowly than if there were no insulation whatsoever, but FG still allows plenty of it.AND IT HAPPENS AT AN INCREASED RATE AS THE TEMPERATURE DIFFERENTIAL INCREASES. In other words, when the outside temp is coldest and heat is most needed inside, the rate of heat loss from the convection loop is greatest. At temps below zero, FG is practically worthless, protecting only from radiant heat loss and not from convection or from conduction heat loss.on the other hand, foam has a stable resistance to heat loss regardless of differential abnd it is always greater than FG
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Makes sense. Thanks.
Convection is the movement between the tiny pockets in the FG, are there not pockets and the same convection in the foam all be it less (which is the key here of course). Just curious about the science.
The key is that FG to work properly must be in continuous contact with both the interior and the exterior surface of the wall cavity. Leave a gap and you have a place for air to circulate by convection, unimpeded. Badly installed FG (read most FG installed) tends to be gappy at the junction between it and the sheathing.
Then there's the issue of convection within the FG batts themselves. The batts slow down the convective flow but don't stop it entirely. Closed-cell foam stops this convective flow entirely. Open-cell foam wouldn't to the same degree. Dense-packed cellulose is probably somewhere in the middle.
But most important is the draft/leak/gap sealing that foam provides, particularly in tough-to-seal places such as rim joists, exterior penetrations, penetrations in the poly VB around electrical boxes etc. It does this draft-sealing job better than anything else can. Worse than the mere heat loss alone, is the fact that these air leaks from interior to exterior carry moisture to places where the water vapour will condense, leading to mold and rot.
OK you long-time BTers- did I preach the correct religion here?
"did I preach the correct religion here?"
Heretical perfection. Be the air.
According to my insulation guys who by the way have recently started applying spray foam but FG is still 80% of their work claim that the strength the foam creates in the framing members is incredible. Especially in under a floor thats above a garage for instance. Here in the niagara reg. of Ontario that cavity (floors of rooms above a garage) code req. R31.
Have any of you guys ran into problems with foam when the mechanicals come back and run pipes for water or venting or wiring etc. in the rim joist areas. Why i ask is i often have to go back and do a better job on the piece of FG insul. the HVAC guy removed to run a heat vent and didn't put back properly. If their is foam in his way what are his options?
Never enough time to do it right but always enough time to do it twice
I get electrical and other mechanical subs out of the way and done with rough in first, before foaming.The strength imparted that you mention is indeed a factor. inspectors and engineeers don't recognize it officially, that I know of, but it really imparts solidity to the skin it covers, important in remo work.
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Hey Piffin,I just want to augment what you said about the strength. Inspectors and engineers don't recognize the structural contribution of the foam composite in a rastra-type ICF wall, either, but it is not inconsequential. Although brittle, that stuff has pretty good compressive strength, which adds to the bending resistance of the completed wall. After all, with 10" blocks, I was able to pour an 8 foot lift without any external bracing when i built my shop, and those walls are straight, too.I knew some guys who used cables to pull a racked old frame house back plumb, then sprayed PU foam into the stud cavities. When the cables came off a day later, the house was perfectly straight, and SOLID. And insulated, to boot.Some years ago I lived on a dirt road, and bought an old E-350 panel van that rattled like a giant tin can with rocks bouncing around in it. I framed it out for wood panels, then had it foamed with 3# PU (roof foam, firm enough to walk on). It cost me about $200 in the early 90's, with me trimming. Then I lined it with 1/2" plywood and 1/4" on the ceiling, and carpeted the walls. That was the quietest Econoline on the road, and always a comfy temp, too. I used to have people rap the body panels..."thud." Followed by, "What did you do to that van?!"Anyhow, my point is that rigid spray foam makes a significant contribution to structure, as well as quashing infiltration and convection. It also retards the spread of fire quite well. The bigger cost buys a lot of incidental benefits that FG cannot hope to match.Bill
The fire retarent statement threw me since the stuff is quite flamable, but I realized that the draft stop irt provides would help control and slow a burn in cerrtain circumstances, theoretically at least.
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the stuff is quite flamable
What "stuff"? Polyurethane provides no fuel to the fire and doesn't really "burn". It is consumed, but at a very high temperature (higher than wood, so who cares). Some foams (EPS, Styrofoam) are consumed at very low temperatures, but they don't burn either in the sense of adding fuel to the fire.
There could be other insulating foams that are flammable, but I don't think any of the major ones are. Could be wrong though.
Edited 12/16/2004 10:38 pm ET by tlambert
Trhow a piece on the fire and watch it go.
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"throw it on the fire"
Okay, my mistake. I get this from SIPs proponents. I don't want to call anyone out, so no links, but this is off a SIP Builder's site:
"Polyurethane’s aged R-value is 7.14 per inch. It is a thermoset material that will only char in the presence of direct flame. Urethane does not support combustion and will not burn or melt. It has a Class 1 fire rating, the best available."
Another one, this from a panel manufacturer:
"Besides the R-value, the fire resistance of the panels generates a lot of builder interest. Polyurethane does not melt, does not sustain combustion and is resistant to most chemicals and solvents. "
I've read similar many times.
However, Piffin and, incidentally, the Journal of Fire Sciences, disagree (with the above statements, not with each other).
http://jfs.sagepub.com/cgi/content/abstract/21/5/343
So it turns out what I wrote is wrong. The DOE does say that SIPs are good in a fire and presumably the same would be true of an E-84 PU foam that filled the cavity (the main advantage is eliminating the chimney effect and sealing the structure so that the fire dies of oxygen starvation):
"For example, in one case where the structure exceeded 1,000°F (538°C) in the ceiling areas and 200°F (93°C) near the floors, most wall panels and much of the ceiling remained intact. An examination of the wall panels revealed that the foam-core had neither melted nor delaminated from the skins"
http://www.eere.energy.gov/consumerinfo/factsheets/bd1.html
(that site won't come up for me today, so I got that one through the
google cache)
Sorry for the misinformation in my last post.
>Polyurethane’s aged R-value is 7.14 per inchThe data I've seen has initial R as 7.14 and aged as 6.5/in.
I really do believe that also has to do with field conditions vs factory conditions. The exact mix of expander, propellant, and urethene, and temperature are all variants that effect the final product.Let's just all call it seven and be happy with that.After all, consider the season.;)
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Don't apologize. Info like this is worth reviewing time and time again.
I would not be suprised if the experts change their recommendations on this a couple of times yet.It could be that some of the urethene products are more fire resistant than others or that some are treated with other chenmicals to prevent flame spread.But it is also true that most codes require that the stuff be covered with a flame resistant material like sheetrock for all living areas. Remeber too that this is probably due in part to the off gassing that occours in high heat.another thing to think about - POLY-urethene is composed of MANY kinds of urethene molecules. The mix is differeent for various differing end products, so not all would be reacting the same.And one further point - the cured properties can vary according to the curing conditions, which can be strictly controlled in the facory as with SIPs but not in field with sprayed on foam.
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Note the JFS is talking about - Polyurethane flexible foam is a very versatile, high quality cushioning material. -I have not seen any flexible foam used for SIPS.BTW, that was in CSI show this week. First appeared that a liquid accelerant had been used in a fire, but it was an old couch and the foam melted and formed a lquid fire pool.
Excellent discussion! I've trying to decide between slow rise polyurethane foam and cellulose for the existing walls of my house. Insulation will be blow in from the interior. On most of the older homes it seems like cellulose is the choice, probably due to the low cost. Has anyone used the slow rise foam??I will be finshing the attic. Since the walls and rafter wills be open I will be using the normal Poly spray foam.Mike K
Amateur Home Remodeler in Aurora, Illinois
"Excellent discussion!"Indeed. I certainly appreciate all the info. It's funny how even if you narrow the insulation discussion just to foam, just to PU foam in fact, it's still darn complex!
yes, foam is made of "pockets" or bubbles, or whatever else we call them, but the foam is totally trapping the vacant air, while the FG lets it move through.
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This lets me show off a bit of trivia...closed cell foam is really only 85-95% closed cells. The others are ill-formed during spraying, plus some have the gas escape over time--weak cell walls, expansion/contraction--when it's replaced by ambient air.
That explains a few things
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Are you saying you can get R21 FG instaled for fifty cents/sq ft?
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faceless batts run 50 cents a sq ft (5 1/2inch) material only.
The reason I said board feet is because I meant board feeet.But there is no ggod reason to have a 5.5" stud cavity ion the first place and definitely no reason to fill it all the way. 3" is more than enough. That is about half as many bf as you are thinking of.and yes, it is stil worth it.
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And by code you can leave a 2 inch air space in the cavity? Fire channel? Of course you could and or likely use 3 1/2" studs?
No reason to waste all that lumber. That idea (2x6 framing) came along in the dark ages of insulation and building science.
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That idea (2x6 framing) came along in the dark ages of insulation
But what if you want to use open cell foam (because it flexes and maintains it's seal as the building settles). It's only R 3.6 per inch, so a 3.5" cavity only would yield R-12.6
I can't remember whether or not this was mentioned, but if you're really looking for top insulation value, it may be worth looking into PU SIPs.
Edited 12/16/2004 2:24 am ET by tlambert
Even with FG, 3.5" walls are the better framing choice. If you want to improve your insulation package with the porrer Rvalued insulations, you add a panel of foam over the face of the studs to add another R7 and make up a thermal break.But most folks arguing here are missing the greatest value of the sprayed in place foam, even tho it has been mentioned several times. I guess you have to experience it to understand it. That is the control of convection currents. Wioth properly installed foam job, the top is sealed against heat loss out and the sill is sealed against inflitration so there are no drafts. A typical house has enough leaks to be equivalent to leaving an egress window open, creating drafts. With Sprayed foam, people find themselves openning windows for fresh air, enen in cold winter weather, because the house can be made so snug. With tight control of these drafts, less radiant resistance is needed. Studies show that 2" in floors, 3" in walls, and four in cielings is all that you need . More than that has no practical payback at all.
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> With Sprayed foam, people find themselves openning windows for fresh air, enen in cold winter weather, because the house can be made so snug.And ideally they'll take this into account in their HVAC, whether it's using a HRV or allowing for other conditioned fresh air source. Ours runs through the dehumidifier, be/c it's silly to be stopping unwanted air infiltration, and then be intentionally bringing in the same moisture-laden, pollen-laden air. It's something that we're aware of by the very nature of the tightness of the shells, and I believe SIPs builders are also aware of. But a frame builder who decides part way through to switch from fg to foam might not think of the HVAC implications except maybe just to downsize the boiler.
Yup, like I pointed out earlier, we aren't just talking about one component here, but a whole system. I'been too busy arguing for the paradigm shift to delve into every detail.;)
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Gotchyer back, Paul.
I think what sums up a lot of the discussions is that you have to experience a foam job to appreciate it. We have all tried something new, a one time or another, and some work and some don't. I don't feel that anyone has been misleading. Digest the material and try it. I will never go back to conventional FG again.
Like the married life, you have to try it to appreciate it.
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Seems no one is talking about icynene which (I've read) has none of the pollutants like formaldehyde and CFCs and HCFC that the other spray-ins have.
Its R 3.6 / in. so its about R22 in a 2X6 wall. Rough quote I got is about twice the price of FG.
While this is kind of a new thread I'll put it here since its on topic:
I'm planning on using the icynene in a 2X6 wall 24" OC
I'm looking for some recommendations for how the rest of the wall cavity should be done to achieve energy-star or better rating. Im going to be installing pine clapboard siding. Do I need more (rigid) foam, air channels behind the clapboard, housewrap, etc? I assume I'll still need a interior vapor barrier.
What about gaskets or caulk under the sole and top plates?
Whats the best way to insulate band joists?
Lotta Qs there.Here is my stabI don't know energy star, only keeping customers warm and happy.The latest urethenes have reduced the formaldehyde to almost nothing. there are a lot of diff products tho so it is worth asking about.urethene gives twice the insulation as you are quoting and blown BIBBs or denspack cells nearly same at far less cost. But the other advantages of foam sprayed in place are still there with your icy spray, some of which are replacing the need for gaskets, etc.spraying the band joist, or sill joist as we call them here, is the best way to take care of the rdaiant heat loss there and to control infiltration that cools the whole house.
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Piffin & Crew, what's the major diff b/w Corbond and Icynene. I quoted Icy on my last job b/c I thought that WAS spray in foam. I've been hearing more about corbond, though. any major pros/cons?_____________________________HomeBase__________________________ LLC
There are two types of spray insulation: polyurethane (closed cells) and polyicynene (open cells). Corbond is polyurethane.
To add to what Cloud saidCorbond is PU, which sets up rigid and has an R-value of R-7/inch of thicknessIcynene sets up softer and more flexible, but is only R-3.6/inch
A Lead Carp friend of mine said the other day that ICY was more "absorbtive" than PU due to it's open cell structure. What's been your experience with this? I would think, if true, it would make ICY a less ideal option than PU in an unvented roof where moisture could... presumably... find a long term home. What do you guys think?
_____________________________HomeBase__________________________ LLC
Edited 12/17/2004 6:02 pm ET by homebaseboston
To add to what cloud hiden said. Corabond is twice the r value per inch compared to icynene. But also cost more to install. Corabond, IMHO is more appropiate when you have limited space for insul. Like inbetween straping and masonary walls. There is also a spray foam available that is soy based.
The Corbond is a urethene type of closed cell foam, with additivwes( I think primarily borates) against mold and insects. The icy is an open celled foam that is not as good at preventing moisture movement
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Even with FG, 3.5" walls are the better framing choice.I'd like to read your thoughts on that, but not here, since I think the answer will divert this thread on foam. So please elaborate, herehttp://forums.taunton.com/tp-breaktime/messages?msg=51554.1That aside, there are also code requirements - walls must be R-13, in which case you would almost make it with icynene (R-12.5 in 3.5" wall)Closed-cell would of course be fine in 2x4 and probably better than in 2x6 both from a resource utilization point of view and from a fire point of view (since I'm sure not going to fill the cavity and build R-38.5 walls).Anyway, I'm still curious about your opinion on my previous question. In frame construction (as opposed to SIPs), I've often seen people recommend lower density open-cell foam because it is more flexible and closes the gaps as a building settles and moves, whereas closed-cell foam is stiff so infiltration cracks open up. I guess you sort of answered by saying that stopping convection currents not infiltration is the main benefit of foam. But long-term, open or closed cell will stop convection currents, but closed might allow more infiltration. Thoughts?Edited 12/16/2004 10:33 pm ET by tlambertEdited 12/16/2004 10:50 pm ET by tlambert Edited 12/16/2004 11:29 pm ET by tlambert
Edited 12/16/2004 11:31 pm ET by tlambert
"That aside, there are also code requirements - walls must be R-13, in which case you would almost make it with icynene (R-12.5 in 3.5" wall)"Actually you would make it.The 12.5 is only for the insulation. You have drywall and an air layer on the inside. And Sheathing and finsihed siding on the outside.It has been a long time since I looked those up, but I think that will give you an extra 1 to 2 R value.
I have no expeerience of closed cell allowing infiltration and studies show that it does not. Will get over to the other link too.
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No reason to get testy.
A board ft is a board foot 12"x12"x1". Why would you want to put in 5 1/2" this would be R-37.5?
People will often put in just about 1" of foam (enough for the dew point) and finish off the insulation with cheaper materials e.g. cells.
I don't think foam is a VB (Dow is careful to call it a vapor retarder rather than a vapor barrier), it is relatively impermeable but has a little permeability. For my bathroom remodel I'm going with 3.5" XPS rigid foam board sealed with a foam gun, with no VB. I decided on XPS because of its slight permeability, if any moisture leaks somewhere it will eventually permeate back out, following some recent theories on basement insulation. I figured for a moist environment like a bathroom, FG is a waste of time and I worry about moisture accumulating in cells (no VB is perfect).
XPS is R-5, polyiso is R-7 but it stabilizes to R-6.x. I decided to keep the isocyans out of the house, that's what killed people in Bhopal. I guess the foam sealant may have isocyans, oh well....
Foam is good stuff, other than the price.
When compared to other techniques and materials, the cost/benefit analysis may not work in its favor in every case.
For example, a cathedral ceiling is a compelling case for foam. Certainly no venting required, and the inpectors will buy into this without a fight.
In the case of a regular crawl space attic, the cost/benefit is less clear. Assuming all the penetrations are carefully sealed anyways, a couple of feet of cellulose is going to be just as good at less cost.
One thing in the plus side for foam is that it makes up for a lot of sloppy air sealing details. Done carefully though, you can get excellent thermal performance using cheaper materials.
A competing technique is a layer of rigid foam under the drywall. This adds a thermal break with the framing as a bonus. I've had good results with this design, and no special equipment is required. Worth comparing. Might come in for less.
thanks for the ideas guys, maybe I should just use the foam around the electrical outlets and also the plumbing.
Either way, I am having a hard time finding a material supplier. Merry Xmas to all, bob
Bob
You can also look at http://www.sprayfoam.org. The foam is expensive, but has many benefits. Air infiltration accounts for a good deal of your heat and cooling load. When you spray foam you can reduce the size of your hvac, or in my case, completely eliminate a second system and just zone the existing big one.
Further saving were had because spray foam allowed me to reduce my roof framing members from 2x10 to 2x8 (saved about $750 there). I also eliminated the venting baffles (another $500 or so I'd guess - including labor to install).
However, take note, that your local inspector may lay an egg when you suggest eliminating venting. I had to get an engineer to sign a letter that my roof could be unvented (+$400) and still had the BI drag butt over approving it. Finally I said "I'm spraying the foam next Monday unless you are here to throw yourself in front of the gun". I also provided him with a ResCheck showing that my roof at R-20 nominal would pass the Model Energy Code. I'd recommend having the plans you submit to the building department specify "unvented, spray foam" insulation. Might save some hassle later. You might want to look at http://www.buildingscience.com, which has recommended roof assemblies for different parts of the country.
Now that I am sprayed (this is a live in remodel), the heat barely runs to keep the house at temp. 4800 sq ft house, about 1/2 of the basement (uninsulated block wall) and 1/2 of the first floor (insulated, but poorly) yet to be sprayed (roof is completely sprayed), the furnace (gas/heat pump dual fuel) runs about 4-5 minutes once per hour to keep the house 30 degrees warmer than outside. Can't wait to spray the rest of the house! (might be another year or so before I get that far).
I too had trouble finding a spray foam person, but I finally dug around and found one. I had to make a fair number of calls though. Where are you? I might be able to find you somebody through my local sprayer, he's pretty well networked.
MERC.
DJMerc.
Amazingly short run time on your system.
I a typcial house, what do you supose teh ratio of heat loss is between a) heat transfer through the insulation and b) heat loss directly through air infiltration?
Interesting question, becuase on the face of it one would focus on the R-Value. And certainly you could pile enough FG in the ceiling to equal your foam, but if the air infiltration is not the same between the installations, as you as, you can have a big difference.
Second related issue: Using poly as a vapor barrier on the interior under the sheetrock. It seems to me that this would go a very long way to eliminating the air infiltration problem in typical FG installation.
My father went this route 30 years ago and with only 2x4 walls has one of the cheapest heating bills in the area.
I can't see how anyone without either the spray in foam or the plastice barrier could come anywhere close to ending air infiltration.
"I a typcial house, what do you supose teh ratio of heat loss is between a) heat transfer through the insulation and b) heat loss directly through air infiltration?"
I guess there are no typical houses, but the numbers I have seen tossed around by folks who study this stuff indicate that 70% convective loss is not unusual. You would think newer structures would be better, but the guys who do blower door tests find a lot of problems. Building practices are often code-driven. Codes focus on very specific things, like R-values and venting. These arbitrary factors do not automatically correlate to an energy efficient structure.
I knew someone would climb all over "typcial". But the spirit of my post, was a general comparison.
"Second related issue: Using poly as a vapor barrier on the interior under the sheetrock. It seems to me that this would go a very long way to eliminating the air infiltration problem in typical FG installation. "It would if it was not full of holes. Mainly electrical, but you do end up with lots of smaller ones. And that is all solvable, but takes lots of work.And with poly it will hold water behind it if you have any leaks. The foam is also a water barrier.
As for water behind the plastic. It drys to the outside. Water between sheetrocka nd the plastic? Well, there is the paint for one and secondly if it gets through the sheetrock it can get back out. Not like you had a pipe break.
I've heard convective heat loss as about 50% or so, but I guess higher than that (and csnow says 70%).
As far as plastic, I don't think much of it. An air barrier has to be installed essentially undamaged, whereas a vapor barrier can have a reasonable number of holes in it. A tiny hole in an air barried will emit significant airflow, whereas the same hole in vapor barrier will emit almost no vapor by diffusion. If you look at that moisture that gets carried by diffusion through material vs. the moisture that gets carried via air leaks, it's a huge difference. Makes the diffusion part of it almost irrelevant. Interestingly enough, my engineer specified an open cell foam and no vapor barrier on the ceiling. He wanted the roof to "dry to the inside" because I used asphault shingles on teh roof. He claims asphault shingles can emit some moisture into the roof deck and we had to let that escape to the inside. Ok fine with me.
I also happened to have lots of cathedral ceilings and barrel vaulted stuff, so I just sprayed my roof deck. I can't tell you how much I am glad I don't have to go crawling through blown in piled up crap to cut a light in or whatever. Not that it happens much, but how nice it is. I go into my attic and come out looking great! Not to mention the attic space is conditioned so my HVAC, etc. is in conditioned space (for even more savings).
I agree that the building industry focuses around R value, which really isn't the whole story. I agree it's easy to see and easy to calculate ROI assuming no convective losses. But convective losses are the bigger part of the problem and the only way to quantify them is via a blower door test and that costs money. So it doesn't get done much. I can only say that it is a whole different house when you seal up every little crack and the temperature stays fairly steady. I have pictures of the foam squezzing out errant nail holes in the OSB and around the wire penetrations into electrical boxes. It's cool stuff and I wouldn't hesitate to use it again, even at the high cost.
MERC.
thanks for all the suggestions guys. I am still very interested in installing this product. I have seen it used before, where they filled up a 2x4 stud wall then super 6mil poly on top. As I live north of toronto by 100 miles it gets very cold here but I think the wind is more of a factor for using the styrofoam. I could use sheets but this does not completely stop drafts. I know this because I have tried it on a previous home. I have also heard it has excellent sound abatement qualities. bob
Couple of answers for you. aslo if you can google up the Corbond "walls that work" and associated studies, it will help answer your questions.First, there is a great difference between FG and foam in th air infiltration scheme. Number one thing is that with a properly foamed hosue, controling the infiltration at the sill level helps control infiltration at the cialing level - for ir to leak out, orther iar has to leak in, so you control it at both ends.Plastic does not prevent the convection l;oop tghat developes in a FG wall insulation, and in the cieling it is laughable when the wind blows.you can also have a hard time sealing plastic around the switch and recepticle boxes and lights.
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Ok, you don't like plastic. If you were not to use foam and not use plastic, what would be second best insulation/vapor barrier/wind block?
sorry about the testiness. I felt I was coming back at you in the same tenor you take in arguing your case, which is simply baseless.I never said I don't like plastic. Waht I pointed out is that it does not do what you assume that it does. We are speaking of whole systems here and not one thing standing alone.
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Gee, I am sorry about my tenor, I never intented to bring the AS out in you. Thanks for your thoughts.
Welcome
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Hi Piffin,
How would you seal off the openings in the back of electrical boxes so that when the foam is sprayed, it doesn't get inside the boxes? I've done some using duct tape, but that's rather cumbersome to seal well around wires. I'm thinking of trying a blob of silicone next. Do you know of anything better? Also is there a preferred way of sealing off the front of the boxes?
We are getting ready for Icynene spray.
Thanks,
kestrel
Tape over front. backs seem to have little intrusion
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Hi Piffin,
Guess I was too worried over nothing.
Thanks,
kestrel