As Gaunt Francis’s competition-winning, zero-carbon Green House nears completion at BRE in Watford, contractor Barratt has commissioned the firm to design a suite of zero-carbon homes, from starter pad to three-bedroom home.

The Green House is due for completion by Barratt next month, when the architect hopes that it will pass airtightness and thermographic tests to prove it has been constructed to meet level six on the Code for Sustainable Homes.

Other demonstration homes built at BRE — Sheppard Robson’s Lighthouse and PRP’s Sigma Home — have so far only achieved code six certification for their designs.

As well as the original three- and four-bedroom townhouse concept, Gaunt Francis has been retained to design two- and three-bed versions, and a ground floor studio flat that could be tucked under a townhouse maisonette. “We’re working on a larger range of house types with a view to giving Barratt a series of manuals on how to build to code six,” said associate Andrew Sutton.

He believes this approach will be workable. “There is always an optimum orientation, but there is also some leeway. Volume housebuilders don’t have a culture of building site-specific, so we are trying to come up with some com-promises,” he said. The new designs will be launched when the Green House is officially opened in May.

To maximise thermal mass, the walls of the house are built in Celcon Aircrete panels jointed with a special mortar system, while the concrete floors are by Milbank.