House Plans Maximize Performance per Dollar

Barbara Miller is executive director of the National Affordable Housing Network.

The floor plan of a high-performance home developed by the National Affordable Housing Network with Habitat for Humanity in mind.

The plans feature an R-60 attic, R-40 walls, and an R-19 floor over an uninsulated crawlspace; a poly air-vapor barrier under sheetrock; an 18,750 Btu per hour output wall-mounted, sealed-combustion gas space heater in the living area; and a fully ducted 75% heat recovery ventilation system. The heating load for the 1,238 ft², four-bedroom residence was calculated at 13,640 Btu per hour (-15°F design outdoor temperature).

The plans are the product of more than 15 years of research and development. They are derived from earlier plans designed by Bob Corbett, now NAHN's director of research, and Wally Hansen. During the mid-1980s, five homes (2,400 ft² each), built according to these earlier plans, were monitored for several years as part of the State of Montana's Superinsulation Project. Detailed multichannel hourly measurements showed annual heating costs of approximately $160-$310. During the winter, the measurements showed that heating was needed intermittently during only three months of the year, rather than the five or six months typical for Montana.

Based on these figures, projections for annual gas heating for the NAHN's 1,238 ft² homes are $50-$150. This estimate was calculated using REM energy modeling software and is applicable to locations with over 7,000 annual heating degree-days.

The Montana project also showed that heat recovery ventilation, when designed and installed in conjunction with the right building envelope, can account for more than 22% of space-heating savings. When outdoor temperatures hover below zero for weeks on end, heat recovery provides substantial energy performance improvements. It also has the side benefit of dramatically improving indoor air quality.

Four of five houses tested in the Montana project were tighter than 1.5 ACH at 50 Pascals (Pa.) at the first diagnostic test. All were readily tightened to under 1 ACH at 50 Pa. Ventilation was designed to operate at approximately 0.27 ACH continuously, with stale air being exhausted at all times. With ASHRAE's current standard calling for a minimum of 0.35 ACH, continuous mechanical ventilation of 0.27 ACH is very powerful and effective.

NAHN house plans also feature solar orientation and shading and high-performance windows.

Plans can be ordered by e-mailing NAHN@nahn.com.

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