Building Basics
Wall Framing Insulated Sheathing
Rigid insulation can be attached to the exterior side of the framing to provide a continuous insulating layer that reduces thermal losses through thermal bridging. It can be installed in addition to or instead of OSB sheathing. There are three primary types of rigid insulation: expanded polystyrene (EPS), extruded polystyrene (XPS), and polyisocyanurate (polyiso).
Wood framing accounts for 24% of conventionally framed walls and 14% of advanced-framed walls. Wood framing has about one-fourth the thermal resistance of most insulation materials and so represents a weak point in the thermal envelope. Insulated sheathing effectively addresses this problem by blocking heat transfer through the studs, reducing drafts, and minimizing moisture problems.
When using rigid foam insulation, you will need to decide whether to use OSB sheathing in addition to the rigid foam or if the rigid foam layer will itself serve as the sheathing. You will also need to determine what will serve as the drainage plane and where this layer will be.