Question: Why do you install two layers of exterior wall sheathing?
Answer: We install ½” CDX plywood to provide strength and a solid nailing surface. Then we install ½’ foam to create a complete insulation envelope of the exterior walls. This foam delivers about a 3.4 R-value where the exterior framing embers are required. Without this insulation there is no insulation where the studs, double plates and window headers are. This makes for a nice snug exterior wall and will pay for itself in added comfort and energy savings.