1" or 1.5" foam roof? | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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gordon kelsey Posted: Apr 16, 2010 02:59 PM	1" or 1.5" foam roof? I live in Palm Springs. I am putting a foam roof on my house, over existing tar and gravel. We will have solar voltaic panels installed in tandem with the foam roof. The bids we have been getting for the roof vary between 1" thick and 1.5" thick. The people bidding at 1" say there is no particular advantage to having 1.5" thick. Can you tell me if you believe there is a worthwhile advantage to having 1.5". I had thought that being in the desert, the more insulation the better. Cost is part of my consideration but if I'm doing this I would like to do it right!
mason Posted: Apr 16, 2010 03:37 PM	You will get a cost benefit from the extra 1/2 inch of foam. So, I would go with it. Of course a lot depends on how the roof assembly is constructed. Cathedral ceiling, yes or no? vented or unvented?; insulation on the underside of the roof deck or the floor of the attic? If it is an unvented cathedral or attic ceiling then the extra 1/2 of foam would be a benefit. Assuming there is no or inadequate insulation on the underside of the roof deck to begin with. If it is a vented attic, then the extra 1/2 inch won't be as cost effective, since the outside temperature is getting in the attic anyway. Be sure you install enough insulation for the codes. An advantage of a foam roof with PV panels is that you don't have to re-roof and disturb the panels. Just recoat every 10-15 years. Recommendation: If you have no insulation presently and it is a cathedral ceiling or unvented attic assembly, then go with 2-3 inches of foam. It would benefit you in the middle of summer.
gordon kelsey Posted: Apr 17, 2010 07:06 PM	Thanks for the advice. There are 2 flat roof areas I will be foaming. There is some insulation between the ceiling and roof but I would suspect not a lot. The house was built in 1979.

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gordon kelsey

Posted: Apr 16, 2010 02:59 PM

1" or 1.5" foam roof?

I live in Palm Springs. I am putting a foam roof on my house, over existing tar and gravel. We will have solar voltaic panels installed in tandem with the foam roof.
The bids we have been getting for the roof vary between 1" thick and 1.5" thick.
The people bidding at 1" say there is no particular advantage to having 1.5" thick.
Can you tell me if you believe there is a worthwhile advantage to having 1.5". I had thought that being in the desert, the more insulation the better.
Cost is part of my consideration but if I'm doing this I would like to do it right!

mason

Posted: Apr 16, 2010 03:37 PM

You will get a cost benefit from the extra 1/2 inch of foam. So, I would go with it.

Of course a lot depends on how the roof assembly is constructed. Cathedral ceiling, yes or no?

vented or unvented?;

insulation on the underside of the roof deck or the floor of the attic?

If it is an unvented cathedral or attic ceiling then the extra 1/2 of foam would be a benefit. Assuming there is no or inadequate insulation on the underside of the roof deck to begin with.

If it is a vented attic, then the extra 1/2 inch won't be as cost effective, since the outside temperature is getting in the attic anyway.

Be sure you install enough insulation for the codes. An advantage of a foam roof with PV panels is that you don't have to re-roof and disturb the panels. Just recoat every 10-15 years.

Recommendation: If you have no insulation presently and it is a cathedral ceiling or unvented attic assembly, then go with 2-3 inches of foam. It would benefit you in the middle of summer.

gordon kelsey

Posted: Apr 17, 2010 07:06 PM

Thanks for the advice. There are 2 flat roof areas I will be foaming.
There is some insulation between the ceiling and roof but I would suspect not a lot. The house was built in 1979.

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