Infill housing developer Postgreen and architectural firm Interface Studio Architects, both of Philadelphia, are embarking on a collaboration to design and build two Passive House infill projects in their city. Originally developed in Germany, the Passive House program has been imported to the United States fairly recently. To date, only about a dozen homes have been built and certified to the Passive House standard by the Passive House Institute US, the program's official certifying body stateside.
A Passive House is essentially a superinsulated structure with a tightly sealed envelope. Taken together, these features minimize heating and cooling loads. "The object is to reduce your heating and cooling load by as much as 90 percent," says Nic Darling, Postgreen's marketing director.* For example, Passive Houses from Postgreen and Interface Studio will achieve R-50 insulation for walls and R-70 for the roofs, according to Brian Phillips, AIA, LEED AP, Interface Studio's owner and principal. With a heat-recovery ventilator to help further reduce heating and cooling loads, a Passive House's HVAC system is smaller compared to that of a typical house and sometimes can even be eliminated.
It's a fairly low-tech concept; Passive Houses don't depend on the latest energy technologies, such as solar panels or geothermal heat pumps. Net-zero energy homes or LEED-certified homes can be achieved in a variety of ways, but there is only one method for achieving a Passive House: superinsulate and superseal. "The Passive House is very scientific. That might make it difficult to become popular here—because there's only one way to skin it," Phillips says. However, he notes that Passive House requirements for mechanical systems and the building envelope far exceed LEED's requirements.
It may not be as sexy or exciting as the U.S. Green Building Council's LEED program, but Passive House design is slowly gaining attention within the American design and building industry. For Phillips, Passive House design is an ideal strategy for urban infill development in Philadelphia, as the concept applied to attached residences simply builds on the insulating properties townhome dwellers have long appreciated. "The Passive House takes that natural condition to its natural conclusion," Phillips explains. "A lot of Passive Houses in Germany are being done out in greenfields by themselves, but it seems that they have a real promising application here in urban settings."
The Postgreen/Interface Studio Passive Houses will be built side by side. Besides being superefficient and providing a healthy indoor environment, both houses also will be affordable. One house (the infill unit) is being treated as a case study for Passive House certification, while the other (the corner unit) will be built to Passive House standards, but will not go through the certification process. Both houses were sold even before Postgreen's marketing materials for them were completed. Both homes are currently in the foundation stage.* The aim is to build the 1,300-square-foot, loft-style infill unit with two bedrooms and one bath for about $100 per square foot to prove that Passive House design can be achieved affordably.
For more Passive House projects:
*This article was updated on March 13, 2009.