Imagine cutting your heating and cooling bill by 90 percent, paying a dime when your neighbor pays $1. The Passive House performance standard is realizing this, while achieving excellent comfort and air quality.
My family lives in a house built to the Passive House standard in Belfast Cohousing & Ecovillage in Midcoast Maine, and our home is heated primarily by the sun, occupants, and appliances. Our neighbors in our community in a 500 square foot home spent $220 to heat last winter and a 1,300 square foot home a mere $335. Naturally, the associated carbon emissions are also much lower, especially considering that many homes in Maine use heating oil.
We had a five-day power outage last winter with below freezing temperatures throughout, including some sub-zero weather. It was only sunny for one day of the outage (thus we lost out on all that passive solar heating), but our house lost a mere 2 degrees a day totaling 10 degrees at the end of the outage. Houses nearby were below freezing within a matter of hours.
The specifics of high-performance houses vary on the climate, with our house being designed for a cold climate. Here are some of the qualities that allow us to reach a high level of energy efficiency:
Air Sealing
Most homes, both new and old have a considerable amount of air enter through the walls, foundation, windows, and doors. Our home is virtually airtight, a fact confirmed by the builder GO Logic with a blower door test during construction, showing how much air enters the home through leaks.
The walls contain structural insulated panels or SIPs, with a foam core sandwiched between two pieces of sheathing. Tape is placed between the panels, creating an air barrier. Great attention is paid in sealing gaps, where two building elements come together, such as where the foundation and the walls meet.
Lots of Insulation
The moral of the story is to keep indoor temperatures stable with continuous insulation. The foundation of our home is lined with rigid foam and there is loose-fill cellulose below the roof. There are two types of insulation in the walls, the SIPs and blown-in insulation.
Triple-pane Windows and Doors
Most homes lose a lot of heat through the windows and doors. With an R value of 7, our windows have the same insulating value as the walls of many homes. Combined with the air sealing, these windows and doors are draft-free, keeping the elements out and the warm air in.
Heat Recovery Ventilation
Ultra energy efficient homes of the past often experienced air quality issues. Because our home is virtually airtight, we need to bring in fresh air to maintain high indoor air quality and to avoid moisture issues.
Our home has a Zehnder heat recovery ventilation system, bringing a constant stream of fresh, filtered air into the home. Before stale air from the bathroom and kitchen exits home, the heat is transferred to the incoming air. Zehnder’s systems are up to 95% efficient, allowing homes to achieve a level of energy efficiency that wouldn’t be possible otherwise. Our home does not have exhaust fans, because unfortunately they vent air out of the home without capturing the heat.
Southern Orientation
Our home is aligned from east to west, so there are lots of south-facing windows. Sadly the trees were cleared on the lot to avoid them shading the solar exposure. On sunny days, sunlight streams in through the south-facing windows and door, heating the home. The angles of the sun are lower in the winter, so we receive very little direct sunlight in the summer (when we don’t want the solar heat).
Thermal Mass
Materials with a high thermal mass help absorb and retain heat, preventing the home from experiencing large temperature swings. In our case, the cement slab warms up through the day from the sun and slowly releases the heat when the indoor temperatures dip.
Cost and Availability
Many of these energy efficiency upgrades have an associated cost, typically adding 5 to 10 percent to the cost of the home. This may change a bit as more domestic products are available that meet these high standards, such as high-quality triple-pane windows and doors, which may need to be sourced from abroad. Relatively few builders are experienced in building ultra energy efficient homes, so it is recommended to seek a builder that is certified by the Passive House Institute.