Installing Rigid Foam Over Roof Sheathing

Install rigid insulation board in multiple layers with joints offset vertically and horizontally between adjacent layers.

Installing rigid foam over roof sheathing.

This type of insulated roof assembly limits thermal bridging through rafters. A helpful hint for installation is to use a straight edge along the cut line to ensure the panels fit best. If you are building a new home there are two basic ways to install rigid foam on the exterior of a wall. After installing several layers of rigid foam above the roof sheathing these workers installed plywood above the rigid foam.

There are three key issues with foam sheathing. Interior moisture can enter the wall from air leaks or diffusion through the wall finish. 1 use a thick enough layer of foam to minimize condensation on its interior face. The exposed edges of the 3 layers of rigid insulation are no longer exposed.

To install measure the foam insulation panels to the roof s dimensions. Use a straight edge knife or utility knife to cut the panels to size. When rigid foam insulating sheathing is installed on the exterior walls of a home the foam can serve as a drainage plane taking the place of house wrap for time and cost savings. Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance.

To serve as a drainage plane the seams in the foam sheathing must be properly taped with sheathing and flashing tapes to provide continuity of the drainage plane at joints between panels. Box beam gable framing new gable overhang is framed in the form of a box beam hanging off of a new layer of roof plywood roof sheathing cantilevered over the top of the 3 layers of rigid insulation. Rigid foam over roof sheathing we are in the process of building a home with all the ceilings in the house paralell to the roof and used 2 x 10 rafters throughout. For extra protection dab a small amount of caulk over each nail used to secure the rigid foam insulation to the plywood.

To lessen heat buildup in the summer we installed dupont tyvec attic wrap on the top of the rafters and then nailed 1 furring strips on top of the rafters then installed the. Install nailbase for cladding. You may need to buy longer roofing nails to reach the plywood through the. The foam can either be attached directly to the studs or the walls can be conventionally sheathed with osb or plywood before the foam is installed.

Rigid foam offers tremendous boost to a home or office s r value. The plywood was fastened through the rigid foam to the rafters with long screws. Exterior foam sheathing is often installed on existing homes as an energy saving retrofit when new roofing or siding is needed.