Helpful? 0

Air barrier with polyiso foam insulation

I am building a house with steel C roof joists (flat) and polyiso 9 inch (3 3" layers) foam underneath. ( all material is reclaimed and free)
Should I use an air or moisture barrier between foam and steel joists? House is in Lexington, Va.

Asked by John Waller
Posted Sat, 01/12/2013 - 10:29

Tags:

1 Answer

Select your preferred way to display the comments and click "Save settings" to activate your changes.
1.
Helpful? 0

John,
I'm not sure what you mean by "moisture barrier." If this is a roof assembly, the primary moisture barrier is your roofing. Most roofing types also require roofing underlayment.

Every insulated roof needs an air barrier. You can create an air barrier with the polyiso (perhaps) or with your drywall ceiling (more dependably). For information on possible shrinkage problems with rigid foam -- shrinkage that could affect your ability to use polyiso as an air barrier -- see this article:
Using Rigid Foam As a Water-Resistive Barrier.

Answered by Martin Holladay, GBA Advisor
Posted Sat, 01/12/2013 - 12:48

Other Questions in Energy efficiency and durability

Thermal energy storage

In Green building techniques | Asked by Jim Pancanke | Oct 21, 14

The Death Of Burberry Sale And How To Avoid It

In PassivHaus | Asked by Lonny Solly | Oct 21, 14

PERSIST vs REMOTE vs SIP ?

In Green building techniques | Asked by Walker Angell | Oct 21, 14

Curbless shower with a PVC liner -- how to terminate the liner at the floor?

In General questions | Asked by john walls | Oct 19, 14

Insulation in old home repair

In Energy efficiency and durability | Asked by Tom Ives | Oct 21, 14
Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!