Open Or Closed Cell Foam For Attic

This type of spray polyurethane foam can be classified into two different types.

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. 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. Do it right and your roof will not rot. Open cell spray foam is a perfectly acceptable insulation product to use in attics.

Most open cell foam has a density of about 5 pounds per cubic foot. Open cell foam weighs 1 2 pound per cubic foot and closed cell weighs 2 lbs per cubic foot. Closed cell foam is much denser than open cell foam. Open cell should be at least 6 inches in depth and closed cell 4 inches or more of each depending on local code.

A foams r value is its resistance to heat flow or in other words how well they insulate. I have open cell in my house since 2004 and i would not use it in a dogs out house. Closed cell foam has a higher r value than open cell foam usually about 6 0 per inch. Lstiburek says to do it for every spray foam attic.

Closed cell foam can also increase the racking strength of attic walls which. These two types of spray foam insulation both contain polyurethane that can be potentially dangerous to the environment and to health upon exposure. Light density open cell spray foam insulation and medium density closed cell spray foam insulation. While the denser closed cell variety does not readily absorb moisture open cell foam can draw it in like a sponge.

There you have it. Others like david butler see his comment below say you need to do it only if a moisture problem develops. Using spray foam insulation in an unvented attic application. The myth that open cell is more economical is bullshit.