# Spray foam under roof decks



## veloguru (Nov 11, 2010)

After some research, i am considering increasing my building envelope by having spray foam applied to underside of roof deck. Should increase efficiency of HVAC in attic and energy costs in general. This process includes the blocking of soffit/ridge venting,(thought being that if moist air cannot enter attic there is no problem with mould etc.) Anyone have any input on pros/cons to doing this? P.S. I know it's pricey, so lets put that down as the first con!


----------



## Grumpy (Oct 8, 2003)

Contact the manufacturer of the shingle you have or intend to install. Some allow it, some don't and some allow it with warranty limitations. In other words you may be throwing your shingle warranty in the trash. 

I am on the fence on this subject. I have installed roofs on a few jobs where there was no ventilation due to this insulation process, and anxiously await real world tests to see how the shingles perform in the next 10 years. I predict premature failure, but we will see in time.


----------



## seeyou (Dec 12, 2008)

Grumpy said:


> Contact the manufacturer of the shingle you have or intend to install. Some allow it, some don't and some allow it with warranty limitations. In other words you may be throwing your shingle warranty in the trash.
> 
> *I am on the fence on this subject. I have installed roofs on a few jobs where there was no ventilation due to this insulation process, and anxiously await real world tests to see how the shingles perform in the next 10 years. I predict premature failure, but we will see in time.*


I've done a number of hot roof installations. I've got two that are nearing 15 years old. I looked at one of them about a month ago. OC Oakridge 30 (or it may be 25 - not sure if it was installed before or after the warranty change) is the shingle on that one and they looked as good as any 15 yr old shingles. I need to arrange a viewing of the other roof (it's not easily accessible), but I don't want to stir up anything. IIRC, that roof is Landmarks.

I've read several test reports and the verdict was that the shingles on the "hot" roof were only an average of a few degrees warmer than over a vented attic, and shingle life would be reduced very little if any. But I'm with you. We'll see.


----------



## apehangeralfy (Oct 26, 2008)

Depends on the system. There is a lot of issues from using a peel-n-stick underlayment and an icynene foam together... cooking plywood, hidden rot till the trusses give out...


----------



## Grumpy (Oct 8, 2003)

Test reports are only tests. I really only partially trust any accelerated test report. At the end of th day, I want to see real world results. 

Different types of hot roofs, Copper. I have seen numerous asphalt shingle roofs instealled over iso insulation with no ventilation and they are all catastrphic failures after 10-15 years. That's why I base my decision about the spray foam beneath the roof deck. Only difference is the location of the foam. I can't understand why one would work and not the other.

As for the warranty change. I highly doubt anything was done to the shingles, just the piece of paper the warranty was printed upon. Like I said, only time will tell and in a few years I will no longer be guessing, and will either embrace the technique or fully shun it. I'm not saying it won't work, just saying I am not ready to put my difinitive guarantee on it "yet".


----------



## seeyou (Dec 12, 2008)

Grumpy said:


> *Test reports are only tests. I really only partially trust any accelerated test report. At the end of th day, I want to see real world results. *
> 
> Different types of hot roofs, Copper. * I have seen numerous asphalt shingle roofs instealled over iso insulation with no ventilation and they are all catastrphic failures after 10-15 years. That's why I base my decision about the spray foam beneath the roof deck. Only difference is the location of the foam. I can't understand why one would work and not the other.*
> 
> *As for the warranty change. I highly doubt anything was done to the shingles, just the piece of paper the warranty was printed upon. *Like I said, only time will tell and in a few years I will no longer be guessing, and will either embrace the technique or fully shun it. I'm not saying it won't work, just saying I am not ready to put my difinitive guarantee on it "yet".


Yeah, exactly. Laboratory tests done by anyone but an independent, diss-interested third party are bound to be skewed and even then can't completely reflect real world scenarios.

On the shingles over iso situation you reference, wasn't there sheathing over the iso? How would you fasten the shingles? If there was sheathing, then I can't see how one situation would be different from the other, unless it was the shingles themselves that were defective.

The two jobs I mentioned were on SIPS structures and I understand that only the warranty changed. I just find it somewhat amusing that the warranty keeps getting advanced while the shingles will likely not last the original 25 years.


----------



## Grumpy (Oct 8, 2003)

See you, on most of the ISO jobs I mentioned it'd be an 1 1/2" ISo and the shinlges were secured with 2" roofing/siding nails. Keep in mind WE did not isntall these, but either bid them or in very few cases were hired to replace them. In the few cases where we were hired, I would specify the Atlas Cross Vent AC insulated and ventilated nail base.


----------



## monticellohomes (Mar 19, 2008)

I've done this with one roof and I think it depends on the situation if I would again. My problem with spraying the roof deck is the shingles and also the size of the envelope. If you spray the roof deck you are now adding that CF to the air you are heating and cooling, with some lower pitch roofs that is fine (the one we did that way was a 4/12 with little attic place or access, so it worked great), if you have a 10/12 I would rather spray the ceiling deck to seal out air and then place some blown insulation on top to help with the R value. The depth of the foam would depend on the manufacturer as far as depth for virtually no air infiltration and the cellulose/fiberglass is a lot cheaper.


----------



## JWRoofing (May 5, 2011)

I've done a lot of work in energy efficient building and design. The spray foam definitely has its merits. The biggest weak point in my opinion is that if there is a roof leak, you won't find out until the wood is rotted. Just make sure you overdo your roof when the roof is installed. Maybe an extra layer of underlayment would be a good choice.


----------



## nickangel (May 25, 2011)

It helps to be on top of a few things - your roof tiles, and if you have pooling water or leaky eaves around your foundation and your basement is sprayfoamed, it won't penetrate which can saturate your foundation. The benefits far outweigh the cons - including the price. As a contractor, it's my ace in the hole.


----------



## nickangel (May 25, 2011)

With sprayfoam, there is no place for condensation - mold is eliminated. It really shines in live-in attics when you spray the roofline, although I'd have to advise against open cell. 2lb closed cell is a vapor stop. I use these guys:

www.ecofitfoam.com


----------

