What is passive house?
The Passiv Haus concept was developed in Germany, with the first project in 1991 to build a ‘house without heating’. Since then it has developed into an international standard for new buildings (both houses and non-domestic) and more recently is applied to retrofit refurbishment. In Bavaria, all public buildings are now built to the standard.
The basic concepts of Passiv Haus are to:
- Provide very high levels of insulation in the roof, walls and floor
- Avoid heat losses through conduction by avoiding ‘thermal bridging’
- Use glazing designed to avoid significant heat losses, sparingly on north-facing elevations
- Make the building air-tight and use heat recovery for controlled ventilation
- Ensure sufficient solar gain for an annual balance of heat losses and gains, using shaded but plentiful south-facing windows
With attention to detailed design, a PassivHaus building is expected to achieve a heat requirement of no more than 15 kWh/m2/year or a heating/cooling load of 10W/m2. In practice, this means that a typical house (150m2) requires just 1.5kW of heat capacity, half the rating of an average kettle, to heat a whole house. Above all Passiv Haus buildings are designed to be comfortable, draught-free and with very little temperature difference throughout the building (no more 4ºC) even close to outside walls and windows. Controlled ventilation allows buildings to have plenty of clean, fresh air but without feeling cold and avoiding build up of humidity, condensation and mould.
Of course, the most attractive feature of Passiv Haus buildings is the low running costs (less than £350 per year for heating a 150m2 house). Simple attention to detail during construction is also an important aspect – tiny holes and cracks allow heat to escape (a house built to building regulations can cost nearly £600 per year more to heat compared to a Passiv Haus building, just due to air leakage alone). Homes built to these standards need to be designed and built with care. Most people associate Passiv Haus buildings with Grand Designs, with huge glazed panels arriving on trucks from Germany. This is no longer the case. More and more houses, whether social or private developments, are being constructed to Passiv Haus standards and at costs not significantly more than usual. Detailing is important but it doesn’t have to be at added expense.
On site, construction workers need to know and understand the principles and the impacts of punching holes in airtight membranes or in leaving big gaps in insulation. This is why we recommend that everyone involved in construction should receive training in Passiv Haus principles – they are still relevant to buildings that are not aimed at gaining the accreditation. Many of the concepts are plain common sense. That is why, at SASIE, we’ve partnered with Target Zero‘s Darren O’Gorman, to bring a no-nonsense practical approach to the Passiv Haus training for installers, covering both building fabric and services. The course offers a valuable accreditation to construction workers and supervisors and provides a gentle, hands-on introduction for building designers, service providers and self-builders.
Passiv Haus is a real eye-opener. You’ll begin to understand just how wasteful we are in terms of losing energy and money in our homes and how little it takes to make big improvements.
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