Zone 2 Vented attic
MTrout
| Posted in General Questions on
We live in Houston and have an attic with soffit and ridge vents.
This is bringing in hot humid air. (100+ degrees 90%+ humidity)
The air handler and ductwork is in the attic.
I’m considering converting the attic to an unvented space, but am confused about vapor permeability for the high outside humidity associated with Houston. Everything I’ve read about making an unvented attic seems to apply to colder/dryer climates.
Should we use closed cell foam under the rafters or do we need to use rigid foam above the roof sheathing?
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Replies
Michael,
If you are trying to decide between two options -- installing rigid foam above the roof sheathing, or installing spray foam on the underside of the roof sheathing -- I urge you to install rigid foam above the roof sheathing, because this method keeps the roof sheathing dry, and because this method limits thermal bridging through your rafters.
For more information on this issue, see these two articles:
Creating a Conditioned Attic
How to Install Rigid Foam On Top of Roof Sheathing