What is a Passive House?

written by Tracey Sludds
26
Aug
2016
Single storey certified passive house with series of flat and pitched roofs with zinc brise soleil canopy to south façade with terraced landscaping and grassed areas.

Across the world the term ‘Passive House’ means many things to many people! 

Historically, the term Passive House was a generic term used by designers to reference a host of general ideas on how to reduce the energy consumption of houses by passive means; passive meaning non active technology such as solar gain. 

Today, the widely used term ‘Passive House’ is associated with a standard for a specific way to construct a building. It comes from the Passivhaus Standard; a German construction concept originally developed for homes. Today this concept is applied to all building types, not just houses, and has become the world’s leading standard in energy efficient design. It is referred to across the world as the Passive House Standard. 

The Passive House Standard is a voluntary building standard, which is energy efficient, comfortable, economic and environmentally friendly at the same time. Passive House/Passivhaus is not a brand; it is a building concept which is open to all, and which has proved itself in practice right across the world, with energy savings for heating up to 75% in comparison to conventional buildings.

The Passive House Concept is one that is easy to understand. It is based on minimising heat losses from the building and maximising heat gains into the building, thus eliminating the need for a conventional heating system. Essentially, a Passive House is a type of solar house which is wrapped up very warm and tight (super-insulated airtight envelope), so that only very little heat is lost. The sun shining through the windows (solar gains) are almost all it takes to heat the building. The remaining heat required is created by the people and appliances in the house (internal gains), such as body heat, cooking, bathing, tv, etc.

Diagram showing the main Passive House components required to achieve the passive house standard.

Typically there are 5 basic principles to a Passive House; optimising (1) Thermal Insulation levels with (2) Thermal Bridge Free design, high thermal performance (3) Passive House Windows, very low air-leakage through the building (4) Airtightness levels, utilisation of passive, solar and internal gains and good indoor air quality maintained by a (5) Ventilation with Heat Recovery system with highly efficient heat recovery levels.   

By creating a well-insulated thermally efficient envelope which makes optimum use of free heat gains from the sun the space heating requirement of a Passive House is minimised, thus resulting in no longer any need for a conventional heating system. (With all the free solar gain and little heat loss you do not need as much heat as a conventional system would give – the house would over heat!)

By creating a building with very low air-leakage, you minimise your heat losses. But you still need to ensure the required volume of fresh air needed for healthy living is provided. Therefore, a mechanical ventilation system is required. (Not to be confused with an air-conditioning system – totally different!)

By creating large high performance glazed areas, designed to optimise the solar gain, a Passive House is naturally well-lit by default. All this natural light combined with the good air quality improves the indoor living and working spaces. (Who said it was only for solar gain!)

By creating a mechanical ventilation system, to deal with continual fresh air supply, you now have by default a way of getting the small remainder of heat you need for your house. This fresh air entering the house is heated by the stale air extracted from the house (but they never touch!) via a heat recovery ventilation unit. This means the mechanical system is now providing two services; supplying ventilated fresh air for healthy living and extracting stale heated air to cover the remaining heat needed.

Exemplar passive house with PHPP, Passive House Planning Pack written across image.

The Passive House Standard Certification process, specifically for new build (see EnerPHit – Passive House Standard for Retrofits for existing buildings), is subdivided into 3 categories; Classic, Plus or Premium. Passive House Certification can be achieved for one of these categories depending on the renewable primary energy (PER) demand and generation of renewable energy, along with all other common criteria; demonstrated within the Passive House Planning Package (PHPP). For more specific information on the certification criteria see Passive House Institute

While the Passive House concept requires superior design and components with regard to orientation, layout, external envelope, air tightness, windows, ventilation, heat recovery and innovative heating technologies, there is no need for the design or the components to add significantly to your build cost. 

With the right Passive House Designer using the Passive House Principals from the start of your design, you can minimise the need for unnecessary artificial lighting and heat, and reduce not only your CO2 emissions but you can reduce your energy bills by 75-90%

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