The Passivhaus Definition

Passivhaus is a standard for housing design developed by Professor Wolfgang Feist of the Passivhaus Institute in Germany. The passivhaus standard sets out a way to reduce energy use for space heating and cooling by 90% compared to a traditional build house.

To meet Passivhaus standard we use software called the Passivhaus Planning Package (PHPP) to enter data specific to the project in question,  such as U-values of walls, cold bridging detail and solar gain.  Our own PHPP expert, working with our structural designers, can then model the design and give a figure for the energy demand. If this figure is too high to meet the standard, then various scenarios will be suggested to alter the design which would bring it to the standard – for clients wishing for a certified building. 

Formally the principle is defined as the total energy demand for space heating and cooling must be less than 15kWh/m2/yr of treated floor area. A standard house uses around 110kWh/m2/yr. As well as this, the total primary energy use for all appliances, domestic hot water and space heating and cooling is less than 120 kWh/m2/yr.

The ways in which the passivhaus principle minimises heat loss

  •  Super air-tight envelope (<0.6 ach – we typically achieve 0.3 ach)
  • Minimal cold bridging in the external frame
  • Controlled internal air quality by mechanical ventilation system
  • Clever design of solar gain and summer shading to maximise winter heat gain from the sun.
  • Use of low energy household appliances and lighting
Of the very small number of homes built in the UK that have achieved formal Passivhaus + certification, our own Weyhill project in Hampshire is among them!

In 2015 the Passivhaus institute introduced two further levels of passivhaus certification for build efficiency:

A Passivhaus plus home (PH+) must not require more than 45 kWh / (m²a) of renewable primary energy. In addition, it must generate at least 60 kWh / (m²a) of energy, based on the surface area, and Passivhaus premium where by the energy requirement is further limited to 30 kWh / (m²a), the energy generation must be at least 120 kWh / (m²a). 

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