Open Or Closed Cell Foam For Attic

Open cell spray foam is a perfectly acceptable insulation product to use in attics.

Open or closed cell foam for attic.

Both low density open cell and medium density closed cell spray foam can be used in an unvented attic to provide the needed thermal resistance and airtightness. Closed cell foam can be over three times that with a density of 1 75 pounds per cubic foot or more. Do it right and your roof will not rot. The myth that open cell is more economical is bullshit.

Lstiburek says to do it for every spray foam attic. Open cell foam weighs 1 2 pound per cubic foot and closed cell weighs 2 lbs per cubic foot. There you have it. Most open cell foam has a density of about 5 pounds per cubic foot.

A foams r value is its resistance to heat flow or in other words how well they insulate. Using spray foam insulation in an unvented attic application. Closed cell foam is much denser than open cell foam. There is 300 difference there but the cost they give you is about a third difference and open cell foam at 12 inches will not give you the performance of 2 inches of closed.

If you do not use the attic for a habitable purpose you might want to keep your thermal barrier on the floor of the attic. Closed cell foam can also increase the racking strength of attic walls which. Open cell foam has an r value of about 3 5 to 3 7 per inch while closed cell foam has an r value of about 6 per inch. Closed cell foam has a higher r value than open cell foam usually about 6 0 per inch.

While the denser closed cell variety does not readily absorb moisture open cell foam can draw it in like a sponge. This type of spray polyurethane foam can be classified into two different types. Others like david butler see his comment below say you need to do it only if a moisture problem develops. Light density open cell spray foam insulation and medium density closed cell spray foam insulation.