Closed Cell Spray Foam With 1 5 Mineral Wool In Attic

Open cell foam is soft and spongy impermeable to air but permeable to moisture and according to the doe has an r value per inch ranging from r 3 6 to r 4 3.

Closed cell spray foam with 1 5 mineral wool in attic. A full 2 5 of fluff or half pound open cell foam which would fully seal everything in the 2x3s will be substantially higher performance and costs about the same as an inch of closed cell foam. The r value of open cell spray foam is about 3 5 per inch although the r value can be different depending on the product. If you want to install spray foam in a stud wall and price is no object then it would seem to make sense to specify closed cell spray foam right. Insulating value and strength.

Spray foam insulation is available in open cell and closed cell. Multiple immediate passes with no wait time may also be applied. With high yield and excellent adhesion it s an. As i noted in a different article air leakage through spray polyurethane foam open cell spray foam only needs to be 3 or 3 5 inches thick to form a decent air barrier.

Once applied closed cell foams become rigid and have an r value range from r 6 to. There are two main types of spray foam. Mineral wool batts for 2 4 walls have an r value of 15 while a standard fiberglass batt made to fit in a 2 4 wall has an r value of 11 or 13. Open cell spray foam has a low density and is many times applied in interior walls and areas that are hard to reach in a home.

Johns manville corbond iii closed cell spray polyurethane foam insulation offers and r value of r 7 per inch and can be applied in a single pass to a maximum of 3 5 inches providing superior thermal performance with seamless air sealing and moisture control in a single step. Open cell spray foam has an r value of about r 3 7 per inch while closed cell spray foam has an r value that may be as high as r 6 5 per inch. Mineral stone wool insulation batts are slightly better insulators than the off the shelf fiberglass batts sold at most lumberyards and home centers. That means if you used foam it green closed cell which is r 7 per inch it s r value for a 3 5 deep wall cavity would be r 24 5.

This is very important in situations where your code requires an r 21 for the wall but you only have a 2 4 stud because closed cell spray foam is the only way you would achieve the required r value to meet code. In these humid attics the moisture is getting through the open cell spray foam by vapor diffusion not via air leakage.