Concept

I mention framing as a solar concept because there are many options in building walls and roofs to maximize insulation value for the time, money, and material invested. Each of those options offers other opportunities: wall thickness, more or less labor, more familiar or less familiar framing details, etc. The right choice is what is best for you to achieve the insulation and air tightness levels you want within your budget – labor and materials.

Application

For the wall framing, I chose to build a double 2x4 wall with a 5” gap. I chose this because I believe it will provide me with the R-value I want (R-40+), minimize thermal bridging, and provide the most assured ability to achieve the air infiltration level I want (0.1 ACH – air changes per hour). More analysis is required to determine how this would compare to other wall systems based on my actual labor costs & infiltration rates and better estimates of other system costs, but that is a topic for later.

For the roof, I used standard 2x10 rafter framing and plywood, topped with a two layers of 2” polyisocyanurate and Zip System sheathing. I will fill the rafters with low-density spray-in-place foam. This will give me the R-80+ value I want and be very air tight. The topping took considerably longer than I expected. I will definitely consider other methods in the future.

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