The absence of central heating at a terrace of new homes at Boundary Close in York meant that the city council had to bend its definition of decent homes to allocate tenants to the new houses. The homes built for York Housing Association according to Passivhaus principles do not require substantial heating, contends their architect Phil Bixby from the firm Constructive Individuals.

Government standards emphasise the use of renewables, but the Passsivhaus approach focuses on reducing energy consumption to an absolute minimum, said Bixby. “The Code for Sustainable Homes and many other targets reward the use of renewable energy sources, whereas it is more efficient to reduce consumption,” he added.  He suspects  that no homes have been built in the UK to the demanding standards set by Passivhaus, whilst it is reasonably common in other European countries. In terms of energy consumption, this development comes very close to Passivhaus standards and the insulation and airtightness levels are also not far off, according to Bixby. The team testing the airtightness said it was the best they had ever seen, he said.

The very limited need for heating is a result of achieving high levels of insulation and airtightness and careful attention to build quality. A timber frame structure made from I joists is used throughout, which, with the use of structural fibreboard webbing, reduces thermal bridging. The external wall sections are far deeper than traditional wall constructions incorporating high levels of insulation.

The wood flanges in the panels need to be far thinner than traditional timber framed building using this system, allowing lower grade timber to be used. The system is also used for the roof, which meant that attic trusses were not needed. The roof space has been left open and can be used by the occupiers as an attic room.

The sole heating source in the two bedroom houses is a single 2kw panel heater in the sitting room with a heat recovery system. An immersion heater is used for the hot water which tops up the heat from the roof mounted solar thermal panels. They are expected to provide about 50% of the requirement. The orientation of the houses and the angle of the roofs were designed to maximise the panels’ effectiveness.

The eight homes have been built on the site of disused garages and courtyards, which had attracted anti social behaviour. They have been designed to avoid the problems of overheating, which can affect lightweight timber framed buildings. The first floor is shaded by overhanging eaves, and balconies on the south side provide shade for the ground floor. The windows can all be opened to provide ventilation. There are extractor ducts in the wet areas including the bathroom and kitchen, which lead to the heat exchanger.

Not bringing gas on site or installing central heating yielded savings to invest in environmental features. The costs came out at only 5% above Housing Corporation guidelines. Rather than go out to tender on the scheme, the architects felt it was important to find a contractor who shared their priorities. “Tenders generally put the emphasis on cost rather than quality,” said Bixby. The architects prepared the scheme as far as securing planning permission and then discussed the project details  with a range of contractors.

“The Corporation is happy with this approach, as long as the costs are properly scrutinised,” said Bixby. In fact the builder they chose was obsessive about detail and was as interested as the architects in the results of the airtightness tests.

The architects have prepared a handbook for the occupiers. “Housing managers need to be more proactive, they need to influence the mindset of the occupiers because these homes need to be lived in in a different way,” said Bixby.  At the very least, they need to understand how the technology works, he added.