What’s the difference between a “passive solar” home and a home built to “Passive House” standards? Is one better than the other?
“Passive solar” is a design approach that was popularized in the 1970s and in which heat from the sun is strategically captured to warm homes. Passive solar’s low-tech approach doesn’t abide by any established standard, but the design principles are consistent: Passive solar homes capitalize on solar heat that radiates through south-facing windows (north-facing windows if the home is in the Southern Hemisphere). As the sun warms the house, the heat is retained via insulation and by use of thermal mass — such as concrete, stones or tile — that stores and slowly releases it.
About 20 years after the popularization of passive solar homes, German physicist Wolfgang Feist founded the Passivhaus Institut (PHI), which formalized “Passivhaus,” a comprehensive energy-efficient building standard that was influenced by early passive solar designs, but which placed more importance on an airtight envelope, high-efficiency windows and conditioned air recovery. By 2010, the newly formed Passive House Institute U.S. (PHIUS) had carved out a place for the extremely efficient, very specific and highly demanding standard in the U.S. market. PHI and PHIUS are now working separately to advance Passive House standards in the United States.
The goal of the standard is to achieve a durable, comfortable home with overall energy savings of 60 to 70 percent compared with conventional new homes, including a 90 percent reduction in space-heating requirements. A home must follow the standard exactly to receive Passive House certification. With the dramatically reduced energy requirements, the need for conventional heating and cooling systems disappears. This frees up financial resources that can instead be used to make a home deeply efficient. Adding renewable energy systems becomes more affordable, because a smaller energy-generation system can now meet the much smaller energy demands of a certified Passive House.
The rigorous Passive House standard doesn’t render passive solar design entirely obsolete, however. Many homes built to the Passive House standard rely on passive solar design as one tactic among many to make the home super-efficient. But Passive House certification goes beyond passive solar details and ultimately offers superior performance. Thanks to modern building techniques and products, Passive House buildings allow for far more design innovation than passive solar homes, particularly for structures without ideal sun exposure. Regardless, buildings should incorporate passive solar techniques before active solar techniques, such as solar panels, enter the picture.
Photo by Rick Pharaoh Photography: Passive House-certified homes combine captured sunshine and high-tech design for increased comfort and deep efficiency.