1 2 Pound Foam Unvented Roof

I live next to an a frame shingles missing never leaks a drop.

1 2 pound foam unvented roof. Sanity check on an unvented roof assembly. R 6 polyisocyanurate rigid foam insulation board. There are two types of spray polyurethane foam high density 2 lb ft3 low perm closed cell and low density 0 5 lb ft3 high perm open cell. We re big fans of fine homebuilding.

The local ahj approved our system with 1 2 pound foam and an unvented roof. There are currently two types of spray polyurethane foam spf insulation used in north american residential construction. Unvented roof assemblies are outlined in the. Ccspf or closed cell medium density spray foam 2 pound or 2 pounds per cubic foot and ocspf or open cell low density spray foam half pound or 0 5 pcf.

R 3 square edge rigid foam board insulation sheathing. Rmax thermasheath 3 1 in. Insulating unvented roof assemblies. Spray foam is especially useful for insulating unvented roof assemblies.

Open cell spray foam is also described as a low density or 0 5 lb foam meaning if you cut a piece of open cell foam into one cubic foot 12 x12 x12 that piece of foam would weigh approximately half of one pound. There are two main types of spray foam. The big deal with unvented roof assemblies is to control condensation or moisture accumulation on the underside of the roof sheathing. If you don t want to use sips or nailbase read this article tolearn the four basic approaches to insulating unvented roof assemblies.

R 7 7 rigid foam insulation. And closed cell spray foam which has a density of about 2 lb. 03 13 2009 08 45 pm. Unvented roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation.

That post through the roof on a 2 1 2 pitch yow. 5 1 2 inches can be filled or almost filled with 1 2 pound open cell foam or you can go with 3 to 4 inches of 2 pound closed cell foam. Just have a contractor install spray foam insulation and you will be much happier with an efficient insulation that actually works and controls moisture. Open cell spray foam which has a density of about 1 2 lb.

In the most recent issue of fine homebuilding martin holladay wrote a piece on insulating unvented roof assemblies. Dana dorsett suggests that he include a 1 1 2 inch air gap under the sheathing then install 12 1 2 inches of half pound open cell foam. R 5 78 rigid foam insulation. The microscopic cells within open cell foam are just that open which give it a soft fluffy feeling.

Last edited by buildinginb ham. We agree that avoiding sheathing rot is critical and that air permeable insulation such as fiberglass or cellulose cannot be used alone.