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 structural wall is a 2x4 stud frame with Zip System exterior sheathing. Over the taped Zip panels, the crew attached two layers of Tuff-R foil-faced rigid polyiso foam insulation (R-7 per inch), fastening the first layer with roofing nails and the second layer with long screws. Tuff-R was chosen because it’s easily available on the local market and functions as a vapor barrier against interior moisture as well as a drainage plane material for exterior bulk water (wind-driven rain). Strapping over the foam, attached with 6-inch GRK RSS structural screws, creates a drainage space and provides nailing for pre-primed cementitious lap siding.
The structural wall is a 2x4 stud frame with Zip System exterior sheathing. Over the taped Zip panels, the crew attached two layers of Tuff-R foil-faced rigid polyiso foam insulation (R-7 per inch), fastening the first layer with roofing nails and the second layer with long screws. Tuff-R was chosen because it’s easily available on the local market and functions as a vapor barrier against interior moisture as well as a drainage plane material for exterior bulk water (wind-driven rain). Strapping over the foam, attached with 6-inch GRK RSS structural screws, creates a drainage space and provides nailing for pre-primed cementitious lap siding.

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 layers of 1.5-inch foil-faced rigid polyiso insulation, for a total-wall R-value of 44. We fastened the first layer with 2-inch roofing nails and fastened the second layer through vertical strapping using 6-inch screws with 1 1/2-inch fender washers.

The exterior foam reduces thermal bridging at the wall studs, and the foil facing supplies a drainage plane for the fiber-cement lap siding applied over vertical strapping ripped from 3/4-inch CDX. The foam seams are taped with Thermax aluminum foil tape.

The truss roof is insulated to R-80 with loose-fill cellulose. The air barrier at the ceiling plane consists of Zip System sheathing nailed to the underside of the trusses. To connect this ceiling air barrier to the air barrier at the wall sheathing, Tyvek was laid down over the wall plate and sealed to the plate’s top and sides. Tape along the interior edges of this flashing completes the seal to the ceiling and the exterior sheathing.
The truss roof is insulated to R-80 with loose-fill cellulose. The air barrier at the ceiling plane consists of Zip System sheathing nailed to the underside of the trusses. To connect this ceiling air barrier to the air barrier at the wall sheathing, Tyvek was laid down over the wall plate and sealed to the plate’s top and sides. Tape along the interior edges of this flashing completes the seal to the ceiling and the exterior sheathing.

Because the farmhouse basement is to be used for cold storage and washing of farm produce, we thermally isolated it from the conditioned living space upstairs by insulating the first-floor joist bays with spray foam insulation. We made the basement ceiling airtight by screwing Zip sheathing to the underside of the floor joists and taping the seams (C). Connecting that airtight floor to the wall system was tricky. We laid a wide strip of Tyvek housewrap down on the foundation sill before framing the floor. After the framing was complete, we taped the Tyvek to the wall sheathing and to the underfloor sheathing with Tyvek tape.

“Avalon” has a full concrete basement that is not conditioned because it serves as a workspace and a storage facility for the organic farm. To isolate the working basement from the living space above, the first-floor joist system was insulated with spray foam and sheathed on the underside with Zip System sheathing, taped at the seams. This sheathing is connected to the Zip sheathing on the outboard face of the exterior wall frame with a strip of Tyvek. The crew sets the Tyvek down on top of the basement wall early in the construction process, before placing and anchoring down the pressure-treated sill. After the floor and walls were framed, this Tyvek was taped to the underside of the basement ceiling and to the face of the first-story wall frame using Tyvek tape.
“Avalon” has a full concrete basement that is not conditioned because it serves as a workspace and a storage facility for the organic farm. To isolate the working basement from the living space above, the first-floor joist system was insulated with spray foam and sheathed on the underside with Zip System sheathing, taped at the seams. This sheathing is connected to the Zip sheathing on the outboard face of the exterior wall frame with a strip of Tyvek. The crew sets the Tyvek down on top of the basement wall early in the construction process, before placing and anchoring down the pressure-treated sill. After the floor and walls were framed, this Tyvek was taped to the underside of the basement ceiling and to the face of the first-story wall frame using Tyvek tape.

The truss roof is insulated to R-80 with loose-fill cellulose (B). At the top of the stud wall, we applied Zip flashing over the wall plate, adhering it to the inside and the outside edges of the plate, and protected it by nailing a strip of Zip sheathing along the top of the top plate. We also sheathed the underside of the trusses with Zip sheathing, taping the seams, and taping the sheathing to the wall plate flashing to complete the air seal.