Rigid Foam Over Roof Sheathing

Installing rigid foam insulation on top of roof sheathing is a great option for commercial buildings and homes with limited space.

Rigid foam over roof sheathing.

Rigid insulation sheathing is made of a rigid plastic foam that is typically sold in 4 8 or 4 10 foot boards. Many homes in more urban areas or other places with dense populations are opting for this method because they can better optimize space. Johns manville polyiso foam sheathing insulation boards provide a continuous layer of insulation to reduce thermal bridging and improve energy efficiency. The boards are available in several thicknesses and r values.

The exposed edges of the 3 layers of rigid insulation are no longer exposed. My best solution is to rip the shingles on the roof leave the current roof sheathing install 1 5 foil faced rigid foam with foil side up add a layer of sheathing over the foam board install a light colored roofing on top. Polyiso consists of a uniform closed cell polyisocyanurate foam core and provides one of the highest r values per inch of any rigid insulation. Add air conditioning to premises on second floor with a split unit.

1 inch and 2 inch thicknesses are common. Not only that foam sheathing will soon be mandated by code in some climate zones. Exterior rigid foam improves air tightness adds r value reduces the chance of condensation in wall cavities and greatly reduces thermal bridging through studs. Exterior foam sheathing is often installed on existing homes as an energy saving retrofit when new roofing or siding is needed.

The purpose of the requirement that rigid foam installed above roof sheathing meet certain minimum r values is to ensure that the roof sheathing stays warm enough during the winter to avoid moisture accumulation and possible sheathing rot. Install rigid insulation board in multiple layers with joints offset vertically and horizontally between adjacent layers. 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. Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance.