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PassivHaus

AJ 28.02.08

Justin Bere of London-based Bere Architects believes that energy-saving German design methodology PassivHaus offers ‘the best route to achieving the UK’s zero-carbon housing goals’. This is a particularly pressing issue due to the government’s aim for all new housing to be zero-carbon by 2016. Bere is working on his practice’s first full PassivHaus, Smoothfield Farm near Ascot, Berkshire, scheduled to complete this year. It’s one of a number of projects being developed under PassivHaus guidelines in the UK (see page 61) as more and more architects and clients push to dramatically cut carbon emissions.

PassivHaus is based on enhancing building envelopes to reduce heating loads to the point that a conventional heating system can be eliminated. Developed from a German-Swedish academic collaboration in 1988, the first PassivHaus buildings were completed in 1991 in Darmstadt, Germany, the same city in which the PassivHaus Institute was founded five years later. Today, over 9,500 PassivHaus buildings have been realised in Germany, over 2,500 in Austria, and approximately 12,500 worldwide. Gavin Hodgson of the BRE estimates that the number of PassivHaus schemes in the UK is in the low hundreds. No exact figures are available because no UK building has attained PassivHaus designation yet, perhaps partly due to the £2,000 price tag for certification.

This low take-up comes despite the BRE’s commitment to PassivHaus – it participated in research shared between eight countries between 1998 and 2001, and developed a UK website (www.passivhaus.org.uk) and English translation of the PassivHaus computer modelling simulations (PHPP).

PassivHaus standards are roughly equivalent to Code for Sustainable Homes level four, two levels below the zero-carbon level six. The design heat load of a PassivHaus must be less than 15kWh/m2/year – which equals the heat that can be transported by the minimum required mechanical ventilation. Joints between materials and components and all service penetrations must be sealed.

Several UK practices are developing projects to PassivHaus standard. Youmeheshe director Simon Beames, whose firm looked to the method for its OKO House (see page 61), says he first encountered PassivHaus through a competition win in 2006 which enabled him to tour several Austrian PassivHaus projects. ‘I was amazed by the similarity between the internal air quality of the houses and the mountain air’, he says.

Beames notes that the biggest difference with the Austrian context is that while ground-source heating and solar panels can be relied upon to top up energy requirements in Austria’s colder climate, the UK market must rely on biomass wood pellet boilers. >>

Eave to PassivHaus standard Features continuous high-performance insulation

Eave which fails to meet PassivHaus standard Accredited by Communities and Local Government, this eave complies with Building Regulations but does not have enough insulation to achieve PassivHaus standard

PassivHaus in Dornbirn, Austria, 1997 Austria has approximately 2,500 exemplar projects

Achieving the PassivHaus standard

• The PassivHaus standard is applicable to residential and non-residential buildings, new builds, and refurbishments

• The heating demand of schemes must be less than 15kWh/m2/year

• Insulation of roofs, walls and floors must achieve a U-value of 0.15W/m2K

• There must be continuous insulation and no thermal breaks

• Triple-glazed windows with a U-value below 0.8W/m2K and thermally insulated frames must be specified

• Airtightness must be 1m3/hour/m2 at a pressure difference of 50 pascals

• A mechanical whole-house ventilation system, which recovers at least 75 per cent of exhaust heat, must be specified