Passive House Design: An Energy Efficient Standard
Passive House construction is a truly energy-efficient, comfortable and affordable building standard.
Wolfgang Feist initiated the Passive House concept in Germany in May, 1988, at a time when low-energy buildings were already the required legal standard for home construction in Denmark and Sweden. “Passive House is not a brand name, but a tried and true construction concept that can be applied by anyone, anywhere.”
Originally The Passive House concept was only used with new residential construction, but today almost any kind of building anywhere in the world can incorporate the Passive House Standard. The International Passive House Association, iPHA, provides a conceptual framework, conferences, training and certifications, certified designers and tradespeople, and software, a PHPP (Passive House Planning Package), to help with energy calculations. The Association also provides building certification, confirming that the project embodies the principles of Passive House construction. In the United States, one can chose to have their building certified through the iPHA or through the Passive House Alliance U.S., PHAUS, and the associated Passive House Institute.
What are Passive House Buildings?
These are airtight environments that use built-in mechanical systems to control the transit of air between inside and outside and to maintain temperature. They require as little as 10% of the energy required for heating and cooling in a conventional home because they use things like proper insulation and appropriate windows for the climate. Even in cold or hot climates, minimal or no alternative energy sources are necessary for heating and cooling because of the airtight construction.
Passive House Design exhibits five basic principles:
Thermal bridge-free design.
Passive House windows.
Ventilation with heat recovery.
Passive House Buildings are airtight to prevent moist air from inside the home or humid air from outside the home in warmer climates from penetrating into the construction and causing mold and poor air quality or structural damage.
- Thermal insulation.
Thermal insulation is part of the building envelope. Free of thermal bridges, thermal insulation is thick and continuous, wrapping around the home. It works like a warm coat. Continuous insulation needs to be applied to the external walls, roof, and the foundation (if the basement is included in the Passive House area).
Some insulations do not ensure airtightness, so a continuous air barrier is needed. Its function is to resist air flow, making the indoor climate more controlled, and therefore, energy efficient.
- Thermal bridge-free design.
Thermal bridges affect the structure by, altering (usually decreasing) the interior surface temperature. A worst case scenario would be this leading to moisture condensation and mold. If the thermal bridges alter the structure by increasing the conductivity of the wall, the building suffers heat loss.
To achieve a thermal bridge-free design the insulation layers should be carefully planned so that the insulation thickness of the structure is continuous, void of any breaks.
- Passive house windows.
Windows are critical in a Passive House plan. Poorly insulated windows are cold on the surface and require active heat to maintain a comfortable temperature in the home. Highly insulated windows contribute significantly to maintaining temperature comfort in the building. More and more manufacturers offer high performance windows appropriate for a Passive House, and iPHA provides a list of certified windows.
It sounds as though the windows in these Passive House Buildings are “fixed,” that is, they do not open. In fact, certified Passive Houses must have at least one openable window per room. There are several reasons for this requirement, including that it is the simplest and least expensive way to create airflow at certain times and in certain climates.
- Airtightness and Ventilation with Heat Recovery.
Good indoor air quality is a top priority in any building. Increasing airtightness improves air quality because it prevents air from passing through the walls where it might pick up dirt, mold, or even fiberglass.
Extreme airtightness requires proper ventilation, therefore, “a ventilation unit with heat recovery is absolutely essential for meeting the requirements for a healthy indoor climate while allowing for significant energy savings.” The controlled air flow provided by these systems as well as a proper air barrier, maintains excellent air quality and prevents thermal discomfort zones due to uneven air distribution. Moreover, increased airtightness from an air barrier allows the HVAC to be more efficient.
Airflow not only maintains air quality but also humidity. Conventional ventilation designers, “tend to dimension the air volumes of home ventilation systems as rather high . . . in order to keep the indoor air humidity low in winter, thus reducing the risk of condensation and the associated mold growth.” There is no such problem in a Passive House Building. Because of thermal insulation, interior surfaces of external components are so warm that even humidity as high as 60% cannot cause condensation. As a result, it is possible to reduce external air quantity slightly during cold periods without worrying about damage from humidity.
Passive House construction, using the methods and technologies pioneered in the 80s and implemented in many environments around the world since then, offers hope for a more sustainable, energy-efficient, affordable future.