Air Control and the Science of a High Performance Home

Submitted by A1DesignBuild, written by Mike Feeney

Those of you around at the time may recall the oil crises in America in the 1970’s. In 1973, Oregon was the first state to implement Odd and Even gasoline rationing, where the day of week you could buy gas was determined by the last digit of your license plate.

Photo courtesy A1DesignBuild

It was during these times that energy efficient homes were born in the US by scientists developing house designs that were super-insulated. The 1976 Illinois Lo-Cal House was engineered to use 60% less energy than the standard home at that time.

Photo courtesy A1DesignBuild

This prototype design was developed by University of Illinois and relied on two features to achieve exceptional performance:

  • Super-insulate the home. R-33 insulation was designed for walls—which still by far exceeds today’s code mandated minimum of R-21!
  • Solar orientation: windows are located on the south wall while limiting them on other walls. Triple glazed windows and deep overhangs are utilized to optimize solar heat gains and losses.

The design also calls for vapor barriers / retarders “to stop air leaks and moisture…” While we now know more about the science behind vapor drive and air leakage control, they knew to incorporate solutions back in the 1970s. Maybe the greatest feature of the design: it incorporated no new technology or labor skills and could be built with readily available materials.

Today, building codes are progressively requiring homes to be highly energy efficient, mandating less use of fossil fuels. Certifying agencies such as PHIUS – the Passive House Institute of the US promote homes that use 40-60% less energy than conventional homes, with initiatives to achieve net zero energy consumed by a home.

Most folks are aware that adding insulation to a home’s envelope results directly in energy savings. However, there is an equally important component to energy efficiency: Air-tightness.

The conditioned (heated or cooled) air in your home that escapes through various leaks in the assemblies equates to energy loss. Leakage can also allow air to wash across insulation layers, reducing their ability to insulate. As early as 1976, as demonstrated in the Illinois Lo-Cal House building, scientists understood that controlling air leakage with air and vapor barrier layers was key to successful energy design.

Photo courtesy A1DesignBuild

Today, air-tightness is mandated by our WA Residential Energy Code, which requires a maximum of 5 air changes per hour for a new home. This is good but still relatively high for A1DesignBuild’s standards—for a recent 1,250 square foot home, this would equate to an opening in a wall large enough for a 13-inch kickball to escape that is always open. We believe we can reduce this whole-house leakage rate to an opening size more equivalent to a softball, through attention to the air barrier and testing of whole-house leakage during construction.

The key here is that, through proven scientific detailing and controlled construction techniques and materials, we are now able to predict air leakage rather than allowing it to be an uncontrolled factor in our homes. Once the home is airtight, we can implement fresh air systems to re-introduce a calculated amount of healthy outdoor air to balance required exhaust air from bathrooms and kitchens. Energy recovery ventilators are now available that have capabilities to recover up to 95% of the energy in the air being exhausted.

High Performance home currently underway.

Whether the project entails energy retrofits to an existing home or a newly constructed home, A1DesignBuild has PHIUS-certified design and construction staff currently implementing energy efficient design and construction projects.

This article was written by A1DesignBuild’s Mike Feeney, Certified Passive House Consultant, Registered Architect and Designer.

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