A building is a Passive house if it meets the following three criteria:1. A comfortable indoor climate is achievable without a separate heating system and without an air conditioning system: for this the annual heating demand may not exceed 15 kWh/(m²a) in accordance with the Passive House Planning Package (PHPP).2. The criteria for thermal comfort must be met for all living areas during winter as well as in summer. The following requirements arise from this:

  • U-values of opaque exterior components must be less than 0.15 W/(m²K).
  • U-values of windows and other translucent building components must be less than 0.8 W/(m²K).
  • Translucent areas oriented towards the west or east (±50°) and translucent areas inclined at an angle of 75° to the horizontal may not exceed 15% of the useful areas behind these or they must be equipped with temporary solar protection with a reduction factor of at least 75%. For south-oriented windows the limit is 25% of the useful areas behind these.
  • The supply air temperatures at the air outlet in the room must not be below 17°. Consistently uniform flow of air through all areas and into all rooms must be ensured (ventilation efficiency). The ventilation must be dimensioned primarily for air hygiene (DIN 1946). Noise emission from the ventilation system must be minimal (< 25 dBA).
  • Houses must have at least one openable opening for outdoor air in each room; air flow through the home must be possible (free cooling in summer).

3. The use of specific primary energy for all domestic applications (heating, hot water and domestic electricity) must not exceed 120 kWh/(m²a) in total. The calculation is carried out in accordance with the PHPP.

The following basic principles apply for the construction of Passive Houses:

Thermal insulation
All opaque building components of the exterior envelope of the house are so well-insulated that they have a heat transfer coefficient (U-value) of 0.15 W/(m²K) at the most, i.e. a maximum of 0.15 watts per degree of temperature difference and per square metre of exterior surface are lost.

Passive House windows
The windows (glazing together with the window frame) should not exceed a U-value of 0.80 W/(m²K), with g-values around 50% (g-value= total solar transmittance, proportion of the solar energy available for the room).

Ventilation heat recovery
Convenience ventilation with highly effective heat recovery firstly allows for a good quality of indoor air, and secondly it helps to save energy. In the Passive House at least 75% of the heat from the exhaust air is transferred to the fresh air again by means of a heat exchanger.

Air tightness of the building
Uncontrolled leakage through gaps must be smaller than 0.6 of the total house volume per hour during a test with a negative pressure/excess pressure of 50 Pascal.

Absence of thermal bridges
All edges, corners, connections and penetrations must be planned and executed with great care, so that thermal bridges can be avoided. Thermal bridges which cannot be avoided must be minimised as far as possible.