A newly completed house in West Yorkshire shows that traditional cavity wall construction can be compatible with Passivhaus standards.
The first certified Passivhaus in the UK to employ traditional cavity wall construction – the Denby Dale Passivhaus project in West Yorkshire – has been completed. Clients Geoff and Kate Tunstall wanted to build a low-energy retirement home in their garden and approached the Green Building Store, who suggested following the German Passivhaus route. Energy consultant Peter Warm and Huddersfield architect Derrie O’Sullivan were contracted to work on the project, and the 118 square metre, three-bedroom house was built by Green Building Store’s construction division (Green Building Company) at a cost of £141,000.
Typical Passivhaus buildings usetimber-frame construction or blockwork walls with external render. Green Building Store director Bill Butcher says, ‘We chose cavity wall construction because most British builders are familiar with the technique and materials could be sourced easily from any builders’ merchant. Cavity wall also met Yorkshire planning requirements for stone exteriors and was affordable for our clients. In addition, masonry construction, including cavity wall, offers a “cave effect” which acts as a thermal mass, helping keep temperatures stable in winter and summer’.
As well as using materials from a local builder’s merchant, specialist materials were sourced from the Green Building Store’s range, including windows, cavity wall ties, airtightness tapes and membranes, and mechanical ventilation with heat recovery systems.
Average UK dwelling stock uses energy at a rate of 278 kWh/m2/annum with space heating accounting for 56 per cent of all domestic energy use. Space heating needs for the Denby Dale Passivhaus are 15kWh/m2/annum, in line with ‘traditional’ Passivhaus designs). Annual space heating costs are expected to be around £75 (at 2010 DECC quarterly prices).
The project has an airtightness of 0.33ac/hr at 50Pa, measured using the Euronorm and Passivhaus method. Passivhaus requirements are 0.6. For Passivhaus certification and Euronorm methodology, the volume of all internal partitions, stairs, floor void etc are discounted in the airtightness calculations, resulting in a lower overall internal volume. The scheme was certified by Warm Associates, an independent low energy building practice and registered Passivhaus certifier under supervision of the Passivhaus Institut in Germany.
Meanwhile CSH assessor Jim Parker of 1st Base Projects has suggested that houses built to the high Passivhaus standard, such as this, may only meet CSH level 3 criteria for Ene 1 (Dwelling Emission Rate), largely because the SAP measures used by CSH fail to properly reflect carbon savings. ‘A Passivhaus dwelling’s energy savings are not realistically represented by its Code for Sustainable Homes ratings’, he claims. ‘Many buildings receiving higher CSH ratings (up to level 6) actually perform worse than the Denby Dale Passivhaus in terms of space heating and airtightness, but gain points in other areas, and sometimes through the use of inefficient and expensive bolt-on renewable technologies.’