The motto of passive house design is “maximize your gains, minimize your losses.” Born in Darmstadt, Germany, passive house standard is a combination of superinsulation, airtight building envelopes, energy recovery ventilation, high performance windows and managing solar gain. In recent years, passive house has been more widely adopted in the United States residential construction industry.
The Breezeway House House, built in 2009, is the first passive house to be built in the western United States certified by the Passive House Institute U.S. It is also one of the first ten passive houses ever built in North America.
Of the many building standards, the owner and architect, Dave Brach, said they chose passive house because “it is the most impactful and meaningful standard for sustainable building.” It provides a premium product for little extra cost.
The major benefits of the passive house are achieved through the structural composition. The Breezeway House makes use of softwood lumber for the structural frame, as well as the exterior siding on the garage.
The spacing of the wood studs in the walls was arranged by the architect in a very specific way to maximize R-value and minimize heat loss in winter and heat gain in summer. The total R-value (resistance to heat flow) was an impressive score of 48 (a typical wall is about R-17).
R-value is the capacity of an insulating material to resist heat flow. Simply put, the higher the R-value, the greater the insulating power. Because of wood’s higher R-value, an insulated wood framed home will be more energy efficient than a similarly insulated home built with steel framing.
Dave Brach, the architect of the Breezeway House, said softwood lumber has a surprisingly high R-value, about 1.25-1.5 per inch (heat flow perpendicular to grain). Brach also chose softwood lumber as it’s a very good choice for eliminating thermal bridging in an energy efficient house, which is the flow of heat across the home’s thermal barrier. This means that the house should stay warmer in the cold winter months and cooler in the summer.
The home has a consistently comfortable temperature, even in extreme summer and winter conditions, and a constant supply of clean filtered fresh air. Furthermore, the house has very low utility bills and low fossil fuel consumption.
The Breezeway uses a 2 kW solar PV system and has an average of about 4400 kW/h of energy from the grid on annual basis. An additional 3 kW of solar would bring the home to net zero annual energy, meaning the total amount of energy used by the house on an annual basis is roughly equal to the amount of renewable energy it creates. This is the goal of passive house: to achieve zero energy with a modest (5 kW) solar system. No other building methodology can achieve this.
Softwood lumber is an important building material for the Breezeway House because it has very low embodied energy and a low carbon footprint. Brach said the benefits of building with softwood lumber versus other materials are obvious. He went on to say, “[Softwood lumber] is natural, durable, strong, beautiful and easy to work with!”