Can a combination of blue Dow board plus blown cellulose work well in an attic?
ZnbyPuTsaM
| Posted in GBA Pro Help on
I live in zone 2B and have an old house with no insulation in the attic. I have no wiring, plumbing, or ductwork in the attic and it is unvented. Advised to spray open cell foam on the attic floor between ceiling joists (2X4 on 24 inch centers). Was hoping 3 layers of blue Dow board with foam around edges between joists to air seal space and provide moisture barrier and then loose blown cellulose on top might work almost as well but for less$$. Please advise.
Paul in Texas
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Replies
Paul,
For the same R-value, cellulose costs less than Dow Styrofoam. If you are planning to blow cellulose into your attic, you can get all of your desired R-value from the cellulose.
You don't need three layers of rigid foam for air sealing. In fact, you don't need any rigid foam at all, although you can use one layer of rigid foam (and canned spray foam around the edges) if you want. If you go this route, one layer of rigid foam is fine.
To air seal a ceiling, many contractors just use caulk and canned spray foam (along with plywood, OSB, or rigid foam for the big holes).