Practical Details for Energy Efficiency

For a tight, energy-efficient house, plan your air-sealing strategy at the framing stage

Installing 1 inch of rigid foam insulation under the basement slab keeps the slab warm enough to prevent moisture from condensing on it. The perimeter insulation between the slab and the colder concrete wall provides a thermal break. The cast-in-place pressure-treated window frames will receive low-e argon-filled windows.

Recessing the band joist 2 inches provides room for exterior rigid foam insulation. To provide an air barrier, the foam is carefully caulked in place with Tremco acoustical sealant.

When the budget allows, 2x6 studs are spaced 24 inches on-center, and 1x3 strapping is installed horizontally at 16 inches on-center. The air space provides a thermal break between the studs and the drywall. Red 3M tape is used to seal seams and tears in the poly air barrier.

When a tub/shower unit is located on an exterior wall, the poly air barrier is installed before the tub goes in. To create a tight air barrier, the poly needs to be taped to the bottom plate of the wall.

Poorly sealed ceiling-mounted light fixtures continuously leak interior air into the attic. When the warm, moist air hits a cold surface, the moisture condenses, leading to mildew or rot.

Here, a forced-air register is installed in a piece of 3/4-inch plywood where it penetrates the attic air barrier. The register boot is caulked to the plywood.

Where this dryer vent penetrates the exterior wall (at bottom of photo), a plywood block provides a surface for taping the poly air barrier. This house has horizontal wall strapping, so there was no need to recess the plywood block between the studs. Note that where the partition meets the exterior wall, the penetrations for the plumbing vent and electrical cable are sealed with urethane foam. The photo also shows an Enviroseal airtight electrical box.

Most dense-pack cellulose systems require the installation of a reinforced polyethylene air barrier. Stapling the poly on the side rather than the edge of the studs helps keep the poly from bulging when the cellulose is blown in place.

Cellulose insulation effectively fills all of the spaces around the bottom chords of roof trusses. Because cellulose is cheap, it can be piled on deep.

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