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Launch Slideshow

Air-Sealing and Insulating, Images 20-27

Air-Sealing and Insulating, Images 20-27

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    Leaving little to chance, the crew caulked all seams between framing members and subfloor.

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    Foam backer rod, sealed with caulk, was used in lieu of expanding foam around window and door jambs.

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    Window sealing was time-consuming, with caulk outlining the metal installation straps and the interior edges of the self-adhering window flashing.

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    Dense-pack cellulose insulation was blown behind a permeable membrane stapled to the studs.

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    Attic ceiling areas were sheetrocked first to support the insulation. Attics received a 16-inch layer of loose-fill cellulose with an R-value of 65.

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    Drywall clips replace lumber backers in wall and ceiling corners.

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    A 7-kW PV array on the shed-dormer roof is projected to supply more than 100 percent of the home's electrical consumption.

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    A digital electric meter displays a constant readout of power delivered to and from the grid.

Drywall

With two-stud corners and backerless wall intersections, we used drywall clips instead of nailers to support drywall corners. Both the hangers and I were surprised at how easy the clips were to use. Their purpose is threefold: First, they reduce lumber usage; second, without a nailer in the way, areas above the top plates and behind wall tees and corners are easier to insulate; and third, they help prevent drywall cracks in the corners where wood movement can otherwise introduce stresses. Cracks aren’t just unsightly; they also can contribute to air leakage through the wall assembly.

The blueboard and skim-coat plaster serve as the primary barrier to air movement through the walls and ceiling. When hanging the sheets, we ran a bead of acrylic caulk at all top and bottom plates, at wall ends, and around all openings, fixtures, and electrical boxes. At drywall clip corners, we simply caulked the vertical seams after installing the board — good insurance should the plaster crack in the corners despite the clips.

Mechanical Systems

This home is heated by forced hot air, with the ducts sized for air conditioning and installed entirely in conditioned space. The furnace is a natural gas-fired Evolution System Plus 95s (800/428-4326, bryant.com) with up to 95 percent AFUE. Instead of installing a cooling-only unit, we used a heat pump that can supply both cooling and heating. It provides heat at temperatures of 35°F and above, relieving the furnace and saving some fuel. A Fantech VHR 1404 (800/747-1762, fantech.net) heat-recovery ventilator delivers the home’s makeup air supply. Both the furnace and the Rinnai RC98HP on-demand water heater (800/621-9419, rinnai.us) are sealed combustion units.

Although the cooling load for the house was calculated at 1 1/2 tons, a 2 1/2-ton 18 SEER unit was the smallest available. It’s possible this could lead to short-cycling of the system; that remains to be seen. Presumably, as tight-home construction becomes more common, smaller systems will, too.

Solar power. On the roof, a 7-kilowatt photovoltaic array of 230-watt OnEnergy panels (800/237-4277, sharpusa.com) helps offset electrical usage, with excess power generation being fed back into the grid.

Home Performance

Effectively air-sealing a home is a tall order, but redundant taping and caulking of seams — along with careful attention to detail — clearly paid off in our preliminary test results. This was confirmed by the blower-door test we did after completing the interior: We achieved .72 ACH50 — nearly 50 percent lower (and better) than the outcome of our preliminary test. Our focus throughout the job on energy and resource conservation has already helped place the home well above the 100 mark required for a LEED Platinum designation.

More important, our efforts will pay back in the home’s overall efficiency and performance. Whenever there’s leeway in a construction budget, I push for higher levels of insulation. Done properly, it’s one investment that can pay for itself fairly quickly and, over time, continue to reduce operating costs.

David Joyce owns Synergy Companies Construction in Lancaster, Mass.