Spray Foam vs. Fiberglass - R-value only?

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Permalink Reply by Hunter Dendy on November 27, 2010 at 5:58pm

I spray foamed the roof deck of my attic (OK I hired someone to do it, a reputable company) so I could finish out the space. The project was put on hold for a while after the insulation went in. When I got back around to starting the work again after several months I couldn't believe how many gaps opened up along the rafters. I don't know if the foam shrank, the wood dried out, or a combination of both, but it happened. I'm not even sure if it's a case of a poor installer, but rather a little talked about potential of the materials. Luckily I had the chance to go back and re-foam these gaps. I think of all the houses I've seen spray foamed and quickly drywalled and could have the same issue on a much larger scale.

It really opened my eyes about the need for quality assurance and blower door testing for ALL insulation/air sealing methods. Spray foam isn't the fool-proof material it's marketed to be. All that said, I was very pleased in the increase in comfort level in my house after foaming it.

The only way I can see to differentiate between fiberglass and foam in REM is through the air infiltration and installation grade (both obviously harder to achieve with batts).

I've heard the diminishing returns bit before, but if it were my house I would insist on the the full R30. You can upgrade fixtures and appliances later, but you only get one chance to get the envelope right.

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Permalink Reply by Evan Mills on November 27, 2010 at 10:44pm

Have been contemplating doing my home's floors with spray foam. Good to hear about your sobering experience. Anyone here have applications in floors?

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Permalink Reply by Jamie Kaye on November 28, 2010 at 4:39am

Evan, I have tested lots of houses with spray foamed floors and that application seems to be far less precarious than the attic with all of it's hard areas to reach areas (like the top plate, valleys, tray ceilings, etc...), and also the difference in venting that the attic has been designed for vs. not to much venting in the floor (except under those tubs :)). The only problems I have seen is with applicators maybe thinking no one is going to come behind them (in those tight crawl space areas) and so they skimp on the thickness and completeness. Behind supply boots and other hard to reach areas are the spots that I see missed sometimes or lightly dusted. Those supply boots (at least here in SC) condensate quickly and wick into the sheathing, so paying extra care there is needed. I still believe it is necessary to check it thoroughly and for my tests, I pressurize the house and then do the inspection.

Hunter, I see those mistake a lot of times. The spray foam doesn't shrink at all. It may pull away from the joists, but that happens immediately during spraying. The foam is done doing its movement within about 30 seconds. These kind of misses at the soffit is what I find the most and seem to cause the most problems here in the Lowcountry of SC. You are so right though...It's the envelope and we need to seal it all!! I also agree, that probably a LARGE majority of the spray foamed houses that were not tested have similar, large problems.

For the Rem/Rate comparison, I used my house, which is spray foamed and I left the CFM50 (infiltration) number unchanged and just changed the ceiling R-value and installation grade. I gave the Spray Foam a Grade 1 and the fiberglass a Grade 3 (for the maximum difference there). I used R-21 for the Spray Foam and R-30 for the fiberglass. The change in the yearly costs, total load and carbon emissions was very, very minimal. I am not nearly qualified enough to debate Martin Holladay, as he is the Energy Nerd, but Rem/Rate software is my nerd and I am reading the results like there are diminishing returns. Of course if I had the extra money to spend, I too would want the most thermal barrier possible and would go to R-30.

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Permalink Reply by Carl Seville on November 30, 2010 at 7:59am

Some thoughts on spray foam from my experience with it: I have primarily used low density, open cell foam on homes that I have worked and consulted on, and I think it is the best product for roofs in moderate climates. Flexible and porous to water, it usually does not pull away from the framing as much as high density, closed cell foam. The open cell is more prone to gaps as it expands so quickly that it often folds over on itself and covers up holes before the installer sees them. It is important to carefully inspect the installation, identify these gaps and get them filled before covering up.

One place where I would only use closed cell is in floors over unconditioned and damp crawlspaces to avoid any condensation on the floor during cooling seasons. I am ambivalent about open vs closed cell in walls, I don't see a downside for either.

I do find it amusing that the until recently when more companies are producing both open and closed cell foam, there has been a fight to the death between the different products. The closed cell sales people seemed to be the nastiest about it, claiming that open cell foam was equivalent to the devil, while the open cell guys mostly just watched and sold their product.

Open cell does have a lower R value, but in moderate climates that doesn't make much difference. I would probably use closed cell in extremely cold climates where it makes more of a difference.

The biggest issue is that spray foam does provide a much better air seal with much less work than any other product. It doesn't however make it perfect. I have always contended that a proper insulation and air sealing job should cost about the same with any product. If you use less expensive air permeable insulation, you spend more money on air sealing. If you use foam you spend less on sealing and more on insulation. Eventually it all evens out. We just need to convince the buying public that insulation shouldn't be sold on price, rather on performance and we will begin to weed out the crappy installers, regardless of the product.

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Permalink Reply by John Nicholas on December 2, 2010 at 9:16am

Jamie,

In our are code would be R-38 for an attic; new homes are standard with R-30 and have been for the last 20 years. Doing a home improvement audit, I find that REM shows very little improvement (ROI of15+ years) when going to R-38 total. If I go to R-50 or R-60 in the attic I can get a good ROI in the 5 - 10 year range.

It seems to me, that REM is considering the whole envelope when calculating heat loss changes for 1 improvement. R-30 in the attic and R-19 in a 2x6 wall will show minimal improvement. R-11 walls show less improvement that R-13 in the wall for the R-30 attic. This is mostly speculation on my part, from the limited experience I have.

I think Hunter is right on. Go for the highest R-Value and also adjust the infiltration numbers to take full advantage of the air sealing qualities of the foam. Do you have a pre-foam blower door number? Make a comparison.

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Permalink Reply by Jamie Kaye on December 2, 2010 at 11:17am

John, every house I have done an air seal verification for was already foamed by the insulation contractor prior to the test. I do record the CFM50 for the ventilation requirements, but normally I run the test at 25 pascals to give me more time to test (keeping a good Delta T). I read David Butler's take on home energy improvements being worth it vs. Solar PV in the comments here. I think that is a great way of thinking about the improvements if we are basing them on their cost effectiveness and ROI. It seems to me that going to R-50 or R-60 with foam would never pay itself as the gains that you are making are continuously diminishing, but the per sq. ft. price of the product remains the same, or close. Maybe style specific though like PassiveHaus or something that uses thermal mass as a means of conditioning. What are the parameters and specifics that you used in order to get a 5-10 year payback?

Carl, I second that emotion "The open cell is more prone to gaps as it expands so quickly that it often folds over on itself and covers up holes before the installer sees them." I don't think its the fault of the installer not seeing them because they are incompetent though, more so it is due to the precarious nature of the product. The blower door and IR do amazing things to uncover these issues, and even then you sometimes have to pull away that top 1" or so to really expose that wind, or uncover the hole (that is where IR helps you even more than blower door alone)! I also agree that you end up paying similar costs with either using a better product or paying more in labor depending on which way you achieve your positive results. I think many of the foam guys still aren't caulking the studs, plates, etc...and only spraying in the cavities and they have a lot of room to improve if they would learn about building science and the diagnostics.

Also Carl, your comment "One place where I would only use closed cell is in floors over unconditioned and damp crawlspaces to avoid any condensation on the floor during cooling seasons." What is the change or a reason why if you had fiberglass existing and had no problems to date (i.e...floors cupping, rot, etc...) that you would only use closed cell? Why if open cell is able to breathe wouldn't it perform just the same as fiberglass, if not a bit better because it will be touching the floor and is an effective air barrier? What is the science that can happen there? I do understand that closed cell will move that condensing surface to the outside of the foam vs. the subfloor or even the paper on the insulation, but I am curious as to why if I had no problems to date and only changing the floor insulation from fiberglass to open cell would that deter me from this more economic version?

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Permalink Reply by Carl Seville on December 2, 2010 at 11:40am

RE My comment regarding closed cell foam on floors, the point I was trying to make is that I wouldn't use open cell foam in a hot climate with a damp crawlspace. With AC on inside, you can create a condensing surface on the underside of the floor and since open cell is pervious to vapor, there is the potential for condensation that is not visible where the foam touches the floor. Closed cell is impervious (relatively) to vapor, so the problem wouldn't likely occur. You theoretically could have the same problem with fiberglass, but I wouldn't both using it in floors as it is almost impossible to install correctly.

Jamie Kaye said:

John, every house I have done an air seal verification for was already foamed by the insulation contractor prior to the test. I do record the CFM50 for the ventilation requirements, but normally I run the test at 25 pascals to give me more time to test (keeping a good Delta T). I read David Butler's take on home energy improvements being worth it vs. Solar PV in the comments here. I think that is a great way of thinking about the improvements if we are basing them on their cost effectiveness and ROI. It seems to me that going to R-50 or R-60 with foam would never pay itself as the gains that you are making are continuously diminishing, but the per sq. ft. price of the product remains the same, or close. Maybe style specific though like PassiveHaus or something that uses thermal mass as a means of conditioning. What are the parameters and specifics that you used in order to get a 5-10 year payback?

Carl, I second that emotion "The open cell is more prone to gaps as it expands so quickly that it often folds over on itself and covers up holes before the installer sees them." I don't think its the fault of the installer not seeing them because they are incompetent though, more so it is due to the precarious nature of the product. The blower door and IR do amazing things to uncover these issues, and even then you sometimes have to pull away that top 1" or so to really expose that wind, or uncover the hole (that is where IR helps you even more than blower door alone)! I also agree that you end up paying similar costs with either using a better product or paying more in labor depending on which way you achieve your positive results. I think many of the foam guys still aren't caulking the studs, plates, etc...and only spraying in the cavities and they have a lot of room to improve if they would learn about building science and the diagnostics.

Also Carl, your comment "One place where I would only use closed cell is in floors over unconditioned and damp crawlspaces to avoid any condensation on the floor during cooling seasons." What is the change or a reason why if you had fiberglass existing and had no problems to date (i.e...floors cupping, rot, etc...) that you would only use closed cell? Why if open cell is able to breathe wouldn't it perform just the same as fiberglass, if not a bit better because it will be touching the floor and is an effective air barrier? What is the science that can happen there? I do understand that closed cell will move that condensing surface to the outside of the foam vs. the subfloor or even the paper on the insulation, but I am curious as to why if I had no problems to date and only changing the floor insulation from fiberglass to open cell would that deter me from this more economic version?

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Permalink Reply by John Nicholas on December 2, 2010 at 1:59pm

Jamie Kaye said:

John, every house I have done an air seal verification for was already foamed by the insulation contractor prior to the test. I do record the CFM50 for the ventilation requirements, but normally I run the test at 25 pascals to give me more time to test (keeping a good Delta T). I read David Butler's take on home energy improvements being worth it vs. Solar PV in the comments here. I think that is a great way of thinking about the improvements if we are basing them on their cost effectiveness and ROI. It seems to me that going to R-50 or R-60 with foam would never pay itself as the gains that you are making are continuously diminishing, but the per sq. ft. price of the product remains the same, or close. Maybe style specific though like PassiveHaus or something that uses thermal mass as a means of conditioning. What are the parameters and specifics that you used in order to get a 5-10 year payback?

Jamie,

I am using a 57 -60 cents per sf of attic quoted by 3 different insallers. 1 does FG only, the 2nd blows both FG and Cellulose; the 3rd Cellulose only. That number is R-28 on top of the existing R-30. Those clients choosing to go ahead are providing feed back that my estimates are within 8 - 10% of actual. Some lower, some higher.

ROI is important, comfort is a biggie as well.

We don't have too many foam installs around. I've only seen 1. If I get a chance to do a QA post foam insall IR - I would try to see of I could include a pre-foam BD also. Just very curious to see how the number improves.

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Permalink Reply by Hunter Dendy on December 2, 2010 at 5:26pm

There's a pretty good argument that closed cell should never be used on wood, and I'm leaning that way myself. The point was that since it's not permeable it will compromise the long term durability of the wall/floor/roof. I think an important concept is that vapor diffusion goes both ways- it not only can wet surfaces, it is also the mechanism by which they dry. There's always a cheap component somewhere in the assembly that will fail at some point- stack vent boot, sealant, gasket etc- and trapped moisture between the closed cell foam and sheathing isn't good. Also, the amount of water that will pass through open cell via diffusion is very minimal, assuming it's air tight. The hygroscopic properties of the subfloor will allow it to store and release (dry) this small amount.

Read Leroy Sloan's comment in this forum post.

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Permalink Reply by Bryce Cramer on December 3, 2010 at 6:23am

Carl
I don't believe you will find condensation on the wood sub-floor due to absorption. For example, take a block of wood and put it in your refrigerator along with a can of soda (or beer if you prefer). Take them out after a while and observe what you find. Although they are both at the same surface temperature, the can will have condensation and the wood will not. This is due to sorption of the moisture into the wood fibers. I may be splitting hairs here, but the point is, you don't necessarily have to have visible condensation for their to be moisture related issues. When dealing with wood, we have to examine the moisture content of the wood, not just observe it.

Carl Seville said:

RE My comment regarding closed cell foam on floors, the point I was trying to make is that I wouldn't use open cell foam in a hot climate with a damp crawlspace. With AC on inside, you can create a condensing surface on the underside of the floor and since open cell is pervious to vapor, there is the potential for condensation that is not visible where the foam touches the floor. Closed cell is impervious (relatively) to vapor, so the problem wouldn't likely occur. You theoretically could have the same problem with fiberglass, but I wouldn't both using it in floors as it is almost impossible to install correctly.

Jamie Kaye said:

John, every house I have done an air seal verification for was already foamed by the insulation contractor prior to the test. I do record the CFM50 for the ventilation requirements, but normally I run the test at 25 pascals to give me more time to test (keeping a good Delta T). I read David Butler's take on home energy improvements being worth it vs. Solar PV in the comments here. I think that is a great way of thinking about the improvements if we are basing them on their cost effectiveness and ROI. It seems to me that going to R-50 or R-60 with foam would never pay itself as the gains that you are making are continuously diminishing, but the per sq. ft. price of the product remains the same, or close. Maybe style specific though like PassiveHaus or something that uses thermal mass as a means of conditioning. What are the parameters and specifics that you used in order to get a 5-10 year payback?

Carl, I second that emotion "The open cell is more prone to gaps as it expands so quickly that it often folds over on itself and covers up holes before the installer sees them." I don't think its the fault of the installer not seeing them because they are incompetent though, more so it is due to the precarious nature of the product. The blower door and IR do amazing things to uncover these issues, and even then you sometimes have to pull away that top 1" or so to really expose that wind, or uncover the hole (that is where IR helps you even more than blower door alone)! I also agree that you end up paying similar costs with either using a better product or paying more in labor depending on which way you achieve your positive results. I think many of the foam guys still aren't caulking the studs, plates, etc...and only spraying in the cavities and they have a lot of room to improve if they would learn about building science and the diagnostics.

Also Carl, your comment "One place where I would only use closed cell is in floors over unconditioned and damp crawlspaces to avoid any condensation on the floor during cooling seasons." What is the change or a reason why if you had fiberglass existing and had no problems to date (i.e...floors cupping, rot, etc...) that you would only use closed cell? Why if open cell is able to breathe wouldn't it perform just the same as fiberglass, if not a bit better because it will be touching the floor and is an effective air barrier? What is the science that can happen there? I do understand that closed cell will move that condensing surface to the outside of the foam vs. the subfloor or even the paper on the insulation, but I am curious as to why if I had no problems to date and only changing the floor insulation from fiberglass to open cell would that deter me from this more economic version?

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Permalink Reply by Al Heath on December 5, 2010 at 6:22pm

If money is problem try spraying 2" of foam for air sealing and then max out the cellulose. Fiberglass batts are really not very good product because of gaps and I almost never use it.

Eventually people will start dying from CO and post-testing will be mandatory and enforced. I always recommend against gas stoves in upgraded houses. Gas stoves are NOT sealed combustion and contribute to pollution greatly. Almost all who have tried a modern electric stove would not go back.

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Permalink Reply by Jamie Kaye on December 6, 2010 at 5:13am

Al, I have heard of the "flash and batt" approach, but there are some problems with that also.

In open cell the condensation point is somewhere around the 2-3/4" mark and in closed cell around 7/8". I have heard of nightmare situations with the closed cell application in cold climates where you end up having waterfalls being created in the walls behind the cellulose or fiberglass on the interior surface of the foam. And with open cell, you don't have an air barrier unless you spray ~ 3" (which is about the minimum you can get anyway with the way it expands).

I personally don't put a great amount of attention on gas stoves because they are normally operating only when someone is cooking. There can easily be some incomplete combustion, but I haven't heard of it being of great concern. I am always concerned about the furnace and water heater, but I personally don't worry to much about gas stoves. If I had my choice, I would much rather cook with gas!!! Much more efficient and easier to control!!

I do agree that with all of the tightening that is going on in construction, the chances are increasing for negative pressure situations. Testing should be on the forefront of all the subcontractors/contractors/owners minds, but all of the suppliers need the education as well. People are already dying from CO, but we need to educate them about the dangers of pressure and what can happen when they begin tightening their houses and changing the dynamics within the system. That in itself is why BPI doesn't allow us to improve (tighten) a house with a ventless fireplace a.k.a. the worst fireplace ever invented!!

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