Passive House Design: Getting back to basics
Passivhaus or passive house design is a building certification. The standards of a passive house certified building are set by the Passive House Institute based in Darmstadt, Germany. You can think of a passive house certified building as a structure that is incredibly well suited for the climate of the area it is built. In areas where cold weather exists, passive house buildings are well sealed against heat loss. Windows and doors in a passive house building are often triple glazed, creating a near air-tight structure in combination with well-insulated walls and few (if any) gaps or “thermal breaks”.
A thermal break is simply an area where heat loss occurs, often due to an intersection of building materials. For example, in a stick-built structure (how most single-family homes are built), the studs are a thermal break. Since insulation is traditionally added between wall studs, heat is able to pass from the interior side of the lumber to the exterior directly through the wood itself. A thermal break might also occur where a deck or porch is attached to the structure. In this case, a thermal break occurs where the bolts fasten to the building, extending from the interior of the structure on through to the exterior. Thinking through ways to minimize this type of heat loss is the primary goal of passive house certification.
A building that is passive house certified must pass a rigorous testing process that includes a scientific measure of where and to what extent air escapes from the interior to the exterior of the building. This test, a measure of air tightness, is called the blower door protocol. The target for passive house certification is an air-tightness below 0.6 air changes per hour at 50 pascals pressure for new building Passive House certification and 1.0 air changes per hour for retrofits.
The concept of a passive house structure is ancient, really. Building to keep bad weather out and the comfortable air in is the reason we build structures to begin with. Native structures were built with this principle in mind - from the stone huts known as trulli in southern Italy to the cliff palace built by ancestral Puebloans in the American southwest. Complicated heating and cooling systems and relatively cheap sources of energy have allowed us to forget the importance of building with climate. With furnaces and air conditioning, we no longer have to rely on the weather and the sun alone to keep us comfortable inside. But this comes at a great cost to our carbon footprint that we can no longer afford. Building to passive house standards is really about reducing energy usage and getting back to basics.
