Find a Professional
Sign Up Log In

TOPIC: Insulation Concerns

Polyisocyanurate shrinks?

Return to Insulation Concerns

Return to Archive

Return to Forum

A roofer said he sometimes prefers to use ABS (not sure if that is exactly what it was. Some sort of foam with a R vaue of like 4 per inch). WHen I asked him about the Polyisocyanurate he said it has a higher R value but shrinks as much as an inch leaving gaps...so insulation vaue is lost. Anyone aware of or can validate this claim?
Guest User

4/16/2010
PolyIso can photo degrade if left in the sun on the edges but this will be a completely covered application. I have never heard of it shrinking as your contractor is suggesting. It is expensive and perhaps that is the basis for his inference. Are you sure that he did not mean EPS foam? Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

4/17/2010
He may very well have meant EPS foam. I hadn't heard of it. The Poly seems to be more a better insulator per inch. I don't see any reason to build my roof up a foot too get the same insulation value I can get with 6 inches of poly. Maybe I am missing something?
Guest User

4/17/2010
I am sorry ... I do not have anything to add beyond what has already been said. Todd Miller
Todd Miller
Isaiah Industries, Inc.

4/17/2010
6" of Poly ISO is a lot. As long as the roof is properly sealed, you can probably get by with 4" of foam. 1.5" air space is more than enough. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

4/18/2010
If I remember they said 6' of poly would get me to an R-38. Am I incorrect? I am all about saving some money because either way this is going to be expensive. What product and depth would you recommend for a dwelling in Anchorage (new building code I believe is R-40, or maybe R-45).
Guest User

4/19/2010
By the way, you have been a TREMENDOUS help in educating me so I can talk to these roofing companies with some confidence and understanding. Thanks.
Guest User

4/19/2010