The Passive House standard is possibly the world’s toughest certification for building energy use reduction. It requires projects to use levels of insulation that are beyond code and to eliminate nearly all air leaks and thermal bridges. It also requires intensive energy modeling. The results are buildings that are inexpensive to operate, exceptionally quiet, and exceedingly comfortable throughout the entire year.
Passive House certifications are not limited to just homes. Passive House buildings can be almost any type of building. The base certification is the Certified Passive House Classic, but projects adding solar can earn Plus or Premium certification. Through EnerPHit certifications, renovation projects can be recognized as well.
Passive House buildings are inexpensive to operate because the criteria limit the allowed amount of heating and cooling losses. The most that a Passive House certified building is allowed to use for heating or cooling is 4.75 kBtu per square foot per year (total energy) or 3.17 Btu/h per square foot (peak load). (Some allowances are made for humidity.) For comparison, this is like limiting a 1,000 square foot Orange County apartment unit to less than one third of a ton of cooling.
Another requirement is for buildings to be virtually airtight. Using a blower door, buildings are required to demonstrate 0.6 air changes per hour or less. By contrast, Title 24 building standards generally assumes that infiltration in new homes is five to seven air changes per hour. This leads to a major misconception about Passive House buildings: buildings that can’t breathe must be stuffy. However, the Passive House standard generally calls for more outside air for ventilation than Title 24 and ASHRAE.
To understand how buildings really operate, Passive House requires intense energy modeling through a proprietary Excel workbook. The inputs into the modeling program must include all areas of thermal bridging. Thermal bridges occur around windows, at wall intersections, or at structural connections. They can leak energy and degrade the overall effectiveness of the insulation. A good understanding of building intersections and the process of calculating the energy loss through thermal bridges can also inform the design and development. This leads to comfortable buildings that maintain their temperatures consistently throughout the day.
For more information on the Passive House standard and similar green building practices, contact Moe Fakih below:
Moe Fakih, Principal
Glen Folland, Associate Director