Rigid Foam Under Roof Sheathing

In warm climates zones 1 through 4 low density open cell spray foam insulation is the typical choice since it is vapor permeable and will allow drying of the exterior sheathing and roof framing if they happen to get wet via diffusion into the interior of the building.

Rigid foam under roof sheathing. They keep your home at a comfortable temperature without the need to crank your heat. Install rigid insulation board in multiple layers with joints offset vertically and horizontally between adjacent layers. Remove existing roofing and non adhered underlayment to expose roof sheathing. 3 benefits of rigid foam sheathing.

Apply continuous air control membrane to existing roof sheathing or implement continuous air control at roof sheathing. In my local area there is a green building consultant that recommends a ci panel which is basically eps foam glued to osb. You can even place it under the foundation slab. Rigid foam insulation also known as insulating boards provide high r values.

A lower layer conventionally nailed to the rafters and an upper layer installed as a nailing surface for the roofing material on top of the rigid foam. Rigid insulation is one of the best tools to reduce your energy costs. 4 of polyiso under 4 of eps all above the original roof sheathing. Nail it around the edges with roofing nails.

Open or closed cell spray foam is applied to the underside of the roof sheathing and additional fiberglass or cellulose insulation is blown in as a cost saving method for meeting high insulation requirements and filling in the cavity space between the rafters to the ceiling deck. More effective insulation with r values ranging from 3 6 to 8 0 rigid foam sheathing has much better insulation per inch than other materials i e. The way this is installed would be the osb to the exterior. We live in zone 5 suburb of chicago and are hopefully about to put rigid foam above the roof sheathing on just the northeast roof portion of our roof.

The illustration shows two layers of osb or plywood roof sheathing. Installed on the roof exterior foam makes the living space below more comfortable and reduces the likelihood of ice dams. Then a second layer of plywood sheathing and asphalt shingles following the steps explained in this article. Plywood has an r value of 1 25 and fiberglass batts have an r value of 3 14.