The term ‘Passivhaus’ refers to a relatively new standard in construction, aimed at creating buildings that are both comfortable to live in and energy efficient.
First developed in Germany in 1988, it is estimated there are currently around 17,000 Passivhaus homes worldwide, including the harsh climatic regions of northern Scandinavia. It is likely these will continue to rise, in response to Government targets and rising energy costs.
Passivhaus homes are successful by relying on three simple design principles. Firstly, energy loss is reduced through installing high levels of Rockwool or similar insulation to create a highly insulated building fabric. Secondly, the structure is made as airtight as possible, by identifying gaps, poor detailing; this may be where there are services running through walls, to gaps at the wall/floor junctions and breaks in insulation. Lastly a mechanical ventilation system with heat recovery is installed, in order to maintain comfort levels, by introducing fresh air into the property, without loss of heat.
Properties installed to this standard do not have conventional heating systems; instead they rely predominately on the effectiveness of an insulated, airtight structure, maximising background heat from appliances and solar gain, which may be offset with a small 3kw heater, incorporated into the ventilation system. Assuming, the occupier is aware and uses the system correctly, this should be more than adequate to meet the average sized homes heating demands all year round.
Passive houses adopt a number of factors, to reduce energy loss in meeting the overall U value of 0.15. These include:
- New triple glazed, argon filled UPVC or similar windows.
- High levels of insulation in roof space and in the wall cavity.
- Whole House ventilation systems with RAC (Run around Coil) heat exchangers
- Removing and/or reducing draughts, air leakage, permeability rates
- Energy saving household appliances, including low energy fridge/freezers, microwaves etc
- Maximising natural daylight, with South facing orientations
The Passivhaus design can be incorporated in new and existing buildings, which is essential when 90% of the building stock in the UK will still be in place in 2050. This can be retrofitted to a range of building types, from modern timber framed gluelam structures to solid wall Victorian properties.
Passivhaus houses need to be carefully designed and installed, without which, problems of condensation may occur, through a process called “thermal or cold bridging”. Condensation is avoided by ensuring there are no thermal breaks, an example of which is to use ‘teplo basalt wall ties’ in wall construction, as steel wall ties conduct heat. This is only ever achievable through detailed knowledge and understanding of building materials, with thorough planning and good design practice.
There are disadvantages to the Passivhaus, (see Advantages and Disadvantages of Passivhaus). A particular difficulty may be ensuring that the existing occupants are aware and continue to follow correct guidelines on how to manage the property correctly, as an open window during winter would result in the Passivhaus principles being tested to the limit.
However, the Passivhaus standard can provide significant cost savings in the long term, reducing the whole life cycle cost of a property. This makes them an increasingly attractive option and a prudent investment for homeowners and property developers as energy costs continue to rise and stricter government legislation is imposed.