To create a conditioned attic with a well-insulated sloped roof in a cold and wet climate, a double-stud wall is paired with raised-heel roof trusses and engineered floor trusses.
Double-stud walls offer a thermally broken wall option that can be easily adapted to meet performance needs in several cold-climate locations by increasing or decreasing the space between the walls to alter the overall R-value. They use common materials and familiar assemblies to create a low-tech, energy-efficient wall with lots of room for thick insulation.
Raised-heel or energy-heel trusses are roof trusses whose top and bottom chords are separated by a vertical 2×4, which essentially extends the exterior wall. This creates a deep enough insulation space over the exterior wall to prevent energy loss, ice-damming, cold ceiling corners, and condensation risks that can lead to mold and rot.
Floor trusses are a resource-efficient engineered product that can span the open-plan layouts popular in today’s homes. These trusses are usually assembled from finger-jointed 2x3s or 2x4s, which are produced from lower grade and leftover lumber. The truss parts are joined with metal connectors. Their open-web design gives them a high strength-to-weight ratio and eliminates the need to drill holes for plumbing and electrical runs. They can easily accommodate ducts, making planning and installation of HVAC systems simple and efficient.
The roof in this detail is vented by using 1×2 strapping and Buffalo board—a type of fiberboard—to create an air space under the roof sheathing, which connects the vented soffit with the ridge vents. The roof is insulated with dense-packed cellulose. As an air barrier and vapor retarder, 6 mil. polyethylene is used behind the drywall on the inside of the vaulted ceiling and continues down the face of the interior framed knee wall, and then under the wall plate to…