Our wall example is part of a zero-energy single-family house built for the tenant farmer of an organic farm in rural Connecticut. The owners wanted a sustainable, healthy, and self-sufficient home. Using REM/Design to analyze the cost-benefit trade-offs, we designed the envelope to keep the home's energy demand low enough that heating and cooling can be supplied by a 1-ton Mitsubishi Mr. Slim mini-split heat pump. That left room in the budget for rooftop solar electricity panels with enough capacity to operate the house at net-zero annually.
The wall is framed with 2x4 studs 16 inches on-center and is sheathed with Zip System OSB panels taped at the joints for airtightness (A). The stud bays are filled with open-cell spray foam insulation. (The original spec was for blown cellulose, but the local insulation contractor charged less to install foam.) Over the sheathing, we applied two...
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