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Tightening Up Homes Tightens Energy Bills
Tight construction is a critical feature of the homes built by EnergyValue Housing Award (EVHA) winners, who develop effective techniques through testing and trial and error.
The air tightness of award entries is substantiated by a blower door test in which the home is pressurized or depressurized with a large fan fitted into a doorway to a test pressure, usually 50 Pascals. Measuring the fan flow needed to maintain test pressure determines the amount of air flowing out of or into the house through crevices in its exterior. While a typical new home registers six or more air changes per hour at test pressure, the 2006 EnergyValue Housing Award winning homes averaged less than three.
The blower door test also helps builders determine where leakage is occurring and where to expand air sealing efforts.
Aspen Homes of Colorado, a 2006 EVHA Gold Winner, uses smoke sticks during a blower door test to help visualize airflow and find leakage. According to Rob Sabin, director of research and development for Aspen, a blower door test is “absolutely vital to determine the unique areas that need attention” for tighter construction.
Strategies commonly used by the EVHA builders to achieve tight homes include:
- Applying a sill sealing product, such as Dow Sill Sealer, before attaching the bottom plate
- Taping house wrap at seams
- Sealing penetrations through walls, top and bottom plates, and the band joist area with expanding foam or caulk
- Sealing the rough opening around windows and doors with low-expanding foam
Other techniques include:
- Avoiding recessed can lights in the top floor sealing
- Using casement windows instead of single- or double-hung windows
- Using an unvented attic with foam insulation at roofline
- Using exterior foam sheathing taped at seams in lieu of housewrap
- Attaching weather stripping around attic access hatches
- Using spray wall insulation, which provides air sealing and insulation in one step (in some cases a vapor barrier, depending on the type of foam)
- Gluing drywall to bottom and top plate with subfloor adhesive to prevent attic air from channeling through the walls
- Installing rigid foam sheathing on exterior walls behind bathtubs and showers
- Taping joints of interior vapor barrier and sealing the vapor barrier at the top plate
“When trying to build a tight home, you can't just rely on one step in the process,” said Sabin. His company has achieved its high standard of air sealing by working closely with the insulating contractor, drywall crew and in-house personnel.
In Aspen Home’s system, the insulation crew seals penetrations to the exterior and foam seals the rim joist and around electrical boxes and attic access doors. The drywall crew, in turn, applies construction adhesive at the top and bottom plate before attaching drywall. Finally, company employees ensure that any miscellaneous openings such as the areas around pre-hung doors are sealed.
Sabin estimates that Aspen Homes’ air sealing package, including third-party blower door testing, costs $500-$1,000, including labor and materials.
Once a home is built tightly, it is a good idea to provide some method of mechanical ventilation, which does not need to be complicated or costly. One of the most cost-effective ways to ventilate homes is to provide a passive air intake duct (typically 4- or 6-inch plastic pipe with damper) to the return side of the central air handler to periodically bring fresh air into the home with a time-based controller.
Applications for the 2007 EnergyValue Housing Awards are now available. For more information about the awards program or to apply, click here.
To learn more about air sealing, consult the guidebook, “Advanced Air Sealing.”
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