When the first Passive House building was built in Germany 25 years ago, the certification system raised the bar for energy efficient buildings by introducing a rigorous performance-based standard. This summer, the Passive House Institute in Darmstadt, Germany, has raised the bar higher with its certification of a multi-unit residential complex in Innsbruck, Austria, and a single-family home in Ötigheim, Germany, under Passive House Plus—a new category that incorporates on-site renewable energy.

Photo courtesy Passive House Institute A house in Ötigheim, Germany, designed by architect Sebastian Früh, is the first single-family residence to achieve certification under the new Passive House Plus rating system.

“The energy supply structure worldwide is transitioning from fossil fuels to renewable sources at an encouragingly rapid pace,” says Jessica Grove-Smith a Senior Scientist at the Passive House Institute. The new standard takes into account storage and transmission losses and balances energy demand and supply for renewable sources, explains Grove-Smith. The intent is to meet the European Union’s standards for Nearly Zero Energy Building (NZEB)—targets that all new buildings must meet by 2020.

This new certification system has some of the same requirements as the “classic” Passive House standard. For instance, both require a building with a super-insulated, airtight envelope that consumes less than 4.7 kbtu/sf/yr for heating and cooling and has fewer than 0.6 air changes per hour at 50 pascals of air pressure. But Passive House Plus has a much lower limit for primary source energy (the amount of energy a building consumes), capping it at 4.18 kWh/sf/yr, compared with 5.57 kWh/sf/yr for basic certification. In addition, in order to achieve Passive House Plus status, a building must generate at least 5.57 kWh/sf/yr renewable energy.

Innsbruck architect Vogl-Fernheim earned Passive House Plus certification for one 16-unit building at the Vögelebichl housing development (another 10-unit building at the complex has been certified under the classic system) by designing a super insulated envelope with R-51walls and an R-63 roof and installing a solar array that supplies about 8.9 kWh/sf/yr. For the house in Ötigheim, Lichtenau, Germany-based architect Sebastian Früh met the new standards by limiting primary source energy to 4.1 btu/sf/yr and installing a 680-square foot solar panel system on the south-facing roof.

Although both projects include PVs, Passive House Plus allows for other alternative energy sources, including wind and biomass. In cases when a site is not suitable for on-site generation, the rating system also permits new off-site renewable energy installations.

In addition to Passive House Plus, the Passive House Institute has also recently introduced Passive House Premium, which increases the amount of renewable energy required, essentially making the building a small power plant. Several projects are pursuing certification under this more stringent standard.

The Passive House Institute U.S. (PHIUS), which split with the original German organization in 2011, has its own program for encouraging net zero energy buildings—PHIUS+—the outcome of a three-year study funded by the U.S. Department of Energy.