Rigid Foam Above Roof Deck

Included with the article was a drawing illustrating a method using layers of polyiso with stacked 2x4 s at the eave.

Rigid foam above roof deck.

The persist approach shown in that article includes rigid foam above the roof sheathing. The assembly that i would like to use would be top to. This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4. More insulation is needed above the roof deck in colder climates and where indoor relative humidity is above 35 in winter.

The bottom layer of a single ply membrane roofing system is the roof deck or substrate. You might be able to get away with keeping the existing roofing in place but i would recommend removing the shingles for a few reasons. Generally 40 of the total assembly r value should be above the roof deck. The first step with roof installation is to prepare the roof deck by getting rid of all dirt dust and contaminants.

Polyisocyanurate insulation above the sheathing and approximately 91 4 in. The roof deck can be plywood metal concrete or wood planks. My question was prompted by your article about using rigid foam insulation above the roof deck. High r value unvented roof assemblies will require a proportionally larger amount of insulation above the roof deck for condensation control.

First removing the shingles allows you to inspect the roof deck and address any questionable areas before encasing the whole thing in foam. However the drawing assumed an attic below with additional batt insulation. Owens corning insulation products help improve thermal performance and control moisture in commercial institutional and. Contributing editor michael maines.

Then 2x4s usually installed on the flat are installed above the rigid foam. With three layers of 11 2 in. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. These 2x4s are extended at the eaves and rakes to create a roof overhang.

Deck for a thick roof rigid foam insulation installed above the roof assembly can create an energy smart roof. The rigid insulation over roof would have controlled the temperature of the condensing surface the underside of the roof deck so that i would not have had to use the spray foam except at the perimeter to provide the air seal to the tops of the walls.