Rigid Foam Exterior Roof Sheathing

Rigid foam must be thick enough to prevent condensation on the roof sheathing.

Rigid foam exterior roof sheathing.

Johns manville polyiso foam sheathing insulation boards provide a continuous layer of insulation to reduce thermal bridging and improve energy efficiency. Foamular family of products brochure pdf v 1588677951000 7 13 mb. By patrick mccombe issue 273 feb mar 2018 when combining exterior foam insulation with fiberglass cellulose or mineral wool roof insulation the foam layer must be thick enough to keep the sheathing temperature above the dew point. Rigid foam sheathing is a form of insulation continuous insulation to be exact that s applied to the exterior of the building.

Rigid insulation sheathing is made of a rigid plastic foam that is typically sold in 4 8 or 4 10 foot boards. A vented attic is basically outdoors so installing rigid foam above your roof sheathing is a waste of money and a waste of rigid foam. Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance. If you have a vented attic it makes no sense to install rigid foam above the roof sheathing.

Nailbase must be vented in high snow load areas. Exterior rigid foam improves air tightness adds r value reduces the chance of condensation in wall cavities and greatly reduces thermal bridging through studs. You might as well put the rigid foam in the branches of a tree in your back yard. Polyiso consists of a uniform closed cell polyisocyanurate foam core and provides one of the highest r values per inch of any rigid insulation.

Exterior foam sheathing is often installed on existing homes as an energy saving retrofit when new roofing or siding is needed. You can install rigid foam on the inside of a wall as well but adding exterior foam increases the r value of a wall or roof without eating up interior living space. Install nailbase for cladding. Foamular insulating sheathing is xps insulation is used as sheathing over all exterior walls in wood or metal framing construction to create an effective insulating envelope over the entire structure.