EnerPHit – Passivhaus for Retrofit

A Passivhaus is an energy-efficient building with all year-round comfort and good indoor environmental conditions without the use of significant active space heating or cooling systems. The space heat requirement is reduced by means of passive measures to the point at which there is no longer any need for a conventional space heating system; the air supply system essentially suffices to distribute the remaining space heat requirement.

A Passivhaus provides a very high level of thermal comfort and whole-house even temperature. The concept is based on minimising heat losses and maximising solar heat gains, thus enabling the use of simple building services.

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The Passivhaus Standard is a specific construction standard for buildings which results in good comfort conditions during winter and summer, without traditional space heating systems and without active cooling. The primary focus in building to the Passivhaus Standard is directed towards creating a thermally efficient envelope which makes the optimum use of free heat gains in order to minimise space heating requirement. Structural airtightness (reduction of air infiltration) and minimal thermal bridging are essential. A whole-house mechanical heat recovery ventilation system (MHRV) is used to supply controlled amounts of fresh air to the house. The incoming fresh air is pre-heated, via a heat exchanger, by the outgoing warm stale air. If additional heat is required, a small efficient back-up system (using a renewable energy source, for example) can be used to boost the temperature of the fresh air supplied to the house.

In order to maintain high comfort levels in any building, heat losses must be replaced by heat gains. Heat losses occur through the building fabric due to transmission through poorly insulated walls, floor, ceiling and glazing as well as from uncontrolled cold air infiltration through leaky construction and poorly fitted windows and doors.

In a Passivhaus, the heat losses are reduced dramatically (through better insulation and airtight detailing) so that internal gains and passive solar gain contribute a relatively high proportion of the total need. As a result of this, a smaller space heating system is therefore required compared to that needed in a conventional poorly performing dwelling.


The Passivhaus Standard is a construction standard developed by the Passivhaus Institute in Germany (http://www.passiv.de). The standard can be met using a variety of design strategies, construction methods and technologies and is applicable to any building type.

The EnerPHit Standard

It is difficult to meet the requirements of Passivhaus for a new build but when retrofitting an existing property this is even more difficult as the orientation and many fabric components have already been provided, with many areas being difficult to retrospectively make cold bridge free.  Though it is possible in many circumstances it is not financially viable, for this reason a retro fit standard for existing homes is being developed, the EnerPHit

 The energy requirement of a house retrofitted to the EnerPHit Standard is:

  • Annual space heating requirement of 25 kWh/(m2a) treated floor area;
  • The total primary energy demand not exceeding 120 kWh/(m2a), regardless of energy source; and
  • The frequency of excessive internal temperature (>25°C) should be limited to ≤10%
  • Air changes per hour  ≤1.0 @ n50