The wall system in this example grew out of a dialogue between the homeowners and the architect. The owners, a visual artist and her retired art-professor husband, approached us with a nearly complete design after working with several other architects and builders. Our challenge has been to realize their distinctive artistic vision for their home, along with their very ambitious energy-efficiency goals, while also working within the hard limits of their budget.

The wall system is a 12-inch-thick, double-2x4 stud wall, sheathed on the outside with 1/2-inch plywood. The interior wall frame is supported by the super-insulated concrete slab foundation; the outer wall is non-load-bearing. The wall is filled with 12 inches of blown-in dense-pack cellulose insulation. The Grace Ice & Water Shield drainage plane, installed over the outer wall sheathing, also serves as a combined water and vapor barrier for the house, reflecting the designer’s assessment that exterior bulk water (wind-driven rain) represents the greatest moisture threat for the building in the Vermont climate. The system is designed to dry to the inside through the Intello Plus membrane. (The house is equipped with an energy-recovery ventilator for heat and humidity control.)
The wall system is a 12-inch-thick, double-2x4 stud wall, sheathed on the outside with 1/2-inch plywood. The interior wall frame is supported by the super-insulated concrete slab foundation; the outer wall is non-load-bearing. The wall is filled with 12 inches of blown-in dense-pack cellulose insulation. The Grace Ice & Water Shield drainage plane, installed over the outer wall sheathing, also serves as a combined water and vapor barrier for the house, reflecting the designer’s assessment that exterior bulk water (wind-driven rain) represents the greatest moisture threat for the building in the Vermont climate. The system is designed to dry to the inside through the Intello Plus membrane. (The house is equipped with an energy-recovery ventilator for heat and humidity control.)

We chose the simple double-stud-wall method for this house mostly because of budget issues. The interior 2x4 wall, framed at 16 inches on-center, supports the first-floor frame and roof system (A). It is tied to the outer wall frame with 4x12-inch gussets sawn from ½-inch plywood and is x-braced with metal straps. The outer wall is sheathed with plywood, covered by a skin of Grace Ice & Water Shield. The 12-inch open cavity in the wall is filled with blown-in dense-pack cellulose (R-43).

To create a high-ceiling effect in the open-plan first story, the floor above is framed with trusses with steel webs left exposed to below. The low-slope roof is framed with wood I-joists (B). At the top of the second story exterior wall, the Ice & Water Shield laps over the wall edge onto the roof sheathing. (The 2x6 eaves overhang was attached afterward.) The roofing material is a fully adhered PVC membrane, so the air and vapor barrier for the wall, located at the outer plywood skin, continues on to the top surface of the roof.

Where the wall meets the roof assembly, the Grace Ice & Water Shield laps over the edge of the roof sheathing. Projecting eaves are framed onto the edge of the roof and sheathed after this wall-to-roof seal is formed. Then, a fully adhered PVC membrane roof is installed over the Advantech sheathing of the low-slope roof, maintaining the home’s air and moisture barrier at the exterior face of the building. The house is built on a reinforced concrete slab foundation, poured in a super-insulated forming system supplied by Branch River Plastics, in Smithfield, R.I. The vapor barrier under the slab, a 15-mil Stego Wrap polyethylene sheet, wraps under the 1/2-inch plywood bottom wall plate, extends up the wall sheathing, and is adhered to the wall sheathing with peel-and-stick membrane, integrating the sub-slab vapor barrier with thewall’s exterior drainage plane and vapor barrier.
Where the wall meets the roof assembly, the Grace Ice & Water Shield laps over the edge of the roof sheathing. Projecting eaves are framed onto the edge of the roof and sheathed after this wall-to-roof seal is formed. Then, a fully adhered PVC membrane roof is installed over the Advantech sheathing of the low-slope roof, maintaining the home’s air and moisture barrier at the exterior face of the building. The house is built on a reinforced concrete slab foundation, poured in a super-insulated forming system supplied by Branch River Plastics, in Smithfield, R.I. The vapor barrier under the slab, a 15-mil Stego Wrap polyethylene sheet, wraps under the 1/2-inch plywood bottom wall plate, extends up the wall sheathing, and is adhered to the wall sheathing with peel-and-stick membrane, integrating the sub-slab vapor barrier with thewall’s exterior drainage plane and vapor barrier.

The foundation for this house is a 6-inch reinforced slab poured in an EPS insulated forming system, as developed by Chris Corson (see "An Affordable Passive House," JLC May/12 and Jun/12). We tied our wall system to this foundation by placing a 12-inch-wide plate of half-inch pressure-treated plywood to span the slab and the perimeter insulation (C). The interior wall plate sits on this plywood plate and is anchored to the concrete slab. The outer wall plate, which does not carry floor or roof loads, rests on the plywood plate above the foam. The 15-mil Stego Wrap vapor barrier under the slab foundation runs under the plywood plate, folds up, and is sealed to the plywood skin of the outer wall frame with peel-and-stick membrane.