Continuous Rigid Insulation Sheathing/Siding

Continuous rigid insulation is a construction solution that provides a thermally efficient building enclosure. Rigid insulation sheathing is made of a rigid plastic foam that is typically sold in 4x8- or 4x10-foot boards. The boards are available in several thicknesses and R-values; 1-inch and 2-inch thicknesses are common. Rigid insulation provides thermal protection and it can also serve as an air and moisture barrier. Continuous rigid insulation provides an effective solution to thermal bridging. Thermal bridging occurs wherever an assembly has a component with a low R-value running from the interior to the exterior, most commonly occurring as wood studs. A layer of continuous rigid insulation on the outside of a home helps to mitigate thermal bridging.

There are three primary types of rigid insulation: expanded polystyrene (EPS), extruded polystyrene (XPS), and polyisocyanurate (polyiso). EPS and XPS are thermoplastics, which are non-cross-linked polymers so they are susceptible to deterioration in high temperatures. Polyiso is a thermoset, which is made up of cross-linked polymers so it has a much higher melting temperature. While properties can vary among specific products, XPS and polyiso tend to be higher density, higher R-value, and lower permeance than EPS. 

Install continuous rigid foam insulation or insulated siding to help reduce thermal bridging through wood- or metal-framed exterior walls.

• Install rigid foam over or in place of plywood, OSB, or other wall sheathing.

• Install over a water-resistant barrier. If rigid foam is rated for water resistance, no other water-resistant barrier is required, if seams in the foam layer are sealed.

• Seal all seams in the rigid foam with a compatible tape; apply tape to clean, dry surfaces.