Extreme Energy Efficiency: Passive Houses in North America

Feb. 24, 2011 — As more homes get designed for very high energy performance – inspired by the Department of Energy (DOE)‘s Builders Challenge or similar programs – the Passive House standard that originated in Europe is finding increased interest among North American designers.

One of the most aggressive building standards out there, the Passive House standard focuses strictly on ensuring energy efficiency and comfort through extremely well-insulated and virtually air-tight buildings that are primarily heated by passive solar and internal gains – with minimal or no active heating. Mechanical ventilation provides fresh air and typically includes heat recovery.

Passive House Background

“Passive House” comes from the German Passivhaus, and refers to any building (not just residential) that meets the ultra-high standard for energy efficiency set by the Passivhaus Institut in Germany, according to the Passive House Institute US. The Passivhaus Institut in Darmstadt, Germany started in 1996 on the heels of a small movement in the 1970s to create super-insulated buildings in North America and northern Europe. More than 20,000 buildings in Europe meet the Passive House standard.

The Passivhaus criteria and recommendations are extremely rigorous: buildings must use about 90 percent less heating and cooling energy than common practice. But part of the initial challenge comes from translating a European standard to the North American market. In fact, the Passive House standard – though very ambitious – is based on whole-building performance, and is flexible enough to work for North American homes using North American building products and materials.

Getting North American Buildings to Qualify

The stringent Passive House criteria limit air leakage and energy use relative to floor area. A unique feature of the Passive House standard is its rigor in requiring minimal space conditioning loads. Where other approaches tend to minimize net energy use through on-site renewable energy, the Passive House standard focuses almost entirely on envelope and HVAC.

Super-efficient construction comes at a cost. Although no-cost and low-cost options such as beneficial orientation and shading conditions can help, most climates require that a Passive House is built from the best building components available. Installation practices need to be outstanding as well. This cannot be achieved at low cost, but in many cases may be economically viable through long-term energy cost savings.

Whether a building meets Passive House criteria is determined through blower door tests and with the Passive House Planning Package (PHPP), an Excel-based tool that simulates building performance, including energy use, peak demand and comfort.

Translating the European-derived criteria and recommendations for Passive Houses to North American metrics and practices can sometimes be a challenge. The Passive House Institute US (PHIUS) is offering trainings and guidance and is working on recommendations specific to the North American market to help dispel any misconceptions that Passive House performance is out of reach for North American manufacturers and designers.

U.S. Tests Passive House Standard

In Europe, where more than 20,000 Passive Houses offer lessons learned, the U.S. Army Corps of Engineers is exploring the standard‘s economic viability. Twenty-two "Passivhaus" homes for U.S. Army personnel are being built in Ansbach, Germany. The Army Corps of Engineers expects that construction to the Passive House standard -- despite 15 percent to 20 percent higher construction cost – achieves the lowest lifecycle cost among available options. Similar conclusions are harder to draw in North America, where substantial Passive House experience is still in the making.

PHUS started certifying in 2008, and only a dozen Passive Houses have been certifieing buildings in the United States so far. With a few dozen in the construction and planning stages, this number will slowly rise and include multifamily housing and commercial buildings. Even with its modest impact to date, Passive Houses are starting to contribute to the greater trend toward highly efficient buildings and building products in and from the United States and Canada.