Rigid Foam Under Roof Sheathing

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.

Rigid foam under roof sheathing.

Many homes in more urban areas or other places with dense populations are opting for this method because they can better optimize space. Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance. Continuous rigid insulation is a construction solution that provides a thermally efficient building enclosure. Install nailbase for cladding.

Installed a new fully adhered membrane to the top of the old board sheathing prior to adding all that rigid insulation. Exterior foam sheathing is often installed on existing homes as an energy saving retrofit when new roofing or siding is needed. Installing rigid foam insulation on top of roof sheathing is a great option for commercial buildings and homes with limited space. Start at the bottom of the roof and place the first piece of rigid foam insulation against the metal flashing starting at the center line.

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. Rigid insulation sheathing is made of a rigid plastic foam that is typically sold in 4 8 or 4 10 foot boards. Nail it around the edges with roofing nails. If the sheathing is on the exterior of the foam then drying isn t a concern because interior vapor will never reach the sheathing and the sheathing will always dry to the exterior especially with any rainscreen.

Gable end detail overhang cut and then rebuilt to hide the thickness of the over roofing rigid insulation. Rigid foam sheathing is a form of insulation continuous insulation to be exact that s applied to the exterior of the building. 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.