In 2007, when John Christophers and his wife, Jo, bought their modest, red-brick Victorian terrace house in Birmingham, England, they knew they had their hands full. Their goal was to expand the living space by about 100%, and do it in a way that would elevate the energy efficiency performance of the whole assembly to an extremely high level.

In Britain, that level is commonly known as Level 6, the highest energy efficiency standard attainable under the Code for Sustainable Homes, Britain’s environmental-impact rating system for homes.

Score a big win for John and Jo. The house, formerly two bedrooms, now includes four bedrooms, about 2,200 sq. ft. of interior space – plenty room for them and their five-year-old son – and it has met the Level 6 performance requirements by producing as much energy as it consumes. Among the very few such residential retrofits in England, the project, called Zero Carbon House, was one of two in the county of West Midlands to win a Manser Medal 2010 award from the Royal Institute of British Architects, which declared the building “full of quirky, delightful and well considered details and is a robust and thoughtful design of exceptional quality.”

Contingency systems

A recent New York Times article on the project noted that the couple purchased the house for about $200,000 and spent about $555,000 on the retrofit, which included removing the radiators, gas stove, fireplaces, and most of the plumbing from the Victorian; re-insulating and air-sealing the exterior walls; installing triple-glazed windows throughout; and constructing an addition that extends the building on one side (in space formerly used for parking) and up high enough so that the house next door doesn’t shade the addition’s pitched roof, which has a photovoltaic array and several solar thermal collectors.

John Christophers, an architect practicing in Birmingham, not only pored over the construction details needed to tie the new and old portions of the structure into a well-insulated, airtight package, he was careful to factor in weather conditions when calculating the performance of the renewable-energy systems. The solar hot water system, for example, includes a heavily insulated, 265-gallon “heat store” tank – about five times bigger than storage cylinders typically used for domestic systems – “so that even in winter on frosty/sunny days we hope to get a reasonable input, which will tide us over if we then get a number of cloudy days,” Christophers noted in comment on a website focused on the project.

The house also is equipped with both a heat-recovery ventilation system (made by Itho UK, a division of Netherlands-based Itho B.V.) and, as backup, a wood-burning stove.