Question

I am putting spray foam insulation in my attic. What is the better option: open or closed cell?

Asked by Gil Morelle
Alpharetta, GA

I live in Atlanta, GA, and have received a handful of estimates to insulate my attic with spray foam insulation. I am hearing conflicting stories on what is the most appropriate product between open and closed cell for my attic. Can you please provide some insight?

Answer

Polly Osborne, FAIA, LEED AP

Answered by Polly Osborne, FAIA, LEED AP

Los Angeles, CA

Polly Osborne Architects

December 16, 2010

The first question I have is whether your attic is vented or non-vented.

If you are planning to spray between the rafters, you need to be concerned about standing moisture rotting your sheathing, as Steve Saunders mentions in his excellent Q&A on this topic, "I'm converting my attic into a non-vented conditioned space. Should I use open cell or closed cell foam to insulate?"

If you are spraying between the rafters, and if the attic is open, I prefer an open cell insulation, because the water doesn't get trapped in it. You will need to check with the local codes, however, because open cell insulation is not always allowed.

Closed cell insulation is useful if you want a vapor barrier, and it has a higher R-value. It is very important not to trap moisture, however, as your structure can very quickly be compromised.

The best thing about foam insulation is that it stops infiltration. Even the finest insulation is not doing its job if the air can get around it, which is often the case with poorly installed insulation of any kind. Was that the reason it was recommended in your case?


For more information:

Read Cynthia Phakos' Q&A "I have a soyfoam insulation estimate for the first floor walls of my 40x80 sq ft home built in 1976. Is $4250 worth it?"

Also, check Alex Georgiou's Q&A "I want to add wall insulation to my 1920 home. I have two locally available options -- Icynene and Tri-polymer foam. Can you advise me?"

Tagged In: spray foam, attic insulation

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