John Christophers’ Zero Carbon House
A home in Birmingham’s Balsall Heath is the first retrofit project to achieve level 6 of the Code for Sustainable Homes
Balsall Heath, Birmingham
Retrofitting existing housing stock is becoming an increasingly important way of helping the UK meet its carbon emission targets. Late last year architect John Christophers completed a project to make his early Victorian two-bedroom semi-detached house more energy efficient as well as extending it to more than double its size.
Christophers used the vacant parking area on one side of the 1840 house to construct a modern extension on ground and first floor levels which increases the floor area from 47sq m to 111sq m, providing a four-bedroom house with a rooftop studio above.
He has just received written verification from the Building Research Establishment following the audit of the design stage, confirming that it has achieved an impressive level 6 or zero carbon of the Code for Sustainable Homes.
Normally retrofits would not qualify for the code, but Christophers’ did because more than half of the project was new-build.
“The code rating is based on the whole house without differentiating between the new and the old,” explains Christophers. “The old house has reached the same very demanding standard as the new.”
He adds: “When I designed my house, there was only the Lighthouse by Sheppard Robson built at the BRE [rated at level 6], but that was a new build and a prototype, no one had attempted upgrading a house to code level 6 before.”
Breeam’s technical director at the BRE, Alan Yates, commends Christophers on the project. “It’s fantastic to see a zero carbon home that builds upon the existing vernacular of the local area and I congratulate the client and project team for an imaginative solution to achieving high levels of environmental performance.”
The development cost £1,160 per sq m and features more than 14 reclaimed materials as well as integrating sustainable building materials such as Neopor insulation, Sumatec clay blocks and Intello Plus internal membrane.
Since its construction, Christophers and his family have held nine open days aimed at raising awareness and an understanding of sustainability and “to evangelise and inspire enthusiasm”, he says.
Sustainable products used
Christophers remodelled the existing building to bring it up to the more exacting new-build standards using a variety of sustainable products.
- The front of the building, the roof and the front portion of the first floor have been retained while the side and most of the rear of the building have been dismantled, extended and rebuilt using some of the original bricks.
- A new top-lit radiating stair — with treads made from reclaimed 200-year-old Canadian honeydew maple, once a floor to a silk factory — slots between the existing brickwork and the extension’s gently curved walls. A double-height space has been created to the rear of the original house.
- The combination of triple-glazed windows and high-performance Intello Plus airtight membrane means the house is now sealed to a level 28 times better than the original. An independent air-tightness test was carried out which demonstrated that it achieved Q50 air-tightness rating of 0.97 m3/m2/hr — more than 10 times better than the Part L building regulations.
- The Enersign triple glazed windows and full height sliding doors leading to the garden have a U-value of 0.65 W/sq m/deg C, which is approximately 14 times better than the original single-glazed windows.
- The 100% recycled waste newspaper Warmcell 500 insulation has been used to line the inside of the existing front elevation of the house and the walls now have a U-value of 0.11 W/sq m/deg C — about 16 times better than before. Warmcell 500 insulation was also used to line the inside of the original roof.
- The old battens, slates, rafters and roofing felt have all been retained, and a new light timber framework constructed below to support the Intello Plus airtight membrane, battens and ceiling. The roofs now have a U-value of 0.08 W/sq m/deg C, about 25 times better than before.
- Throughout both the old and new elements, the floors have been made of 75mm-thick rammed earth dug from the foundations and mixed with extra red clay. The surface has been oiled and finished with beeswax polish, and is not only ecologically friendly but adds thermal mass.
- The main load-bearing structure that comprises the rear and side elevations of the three-storey new-build uses unfired hydraulically compressed clay blocks which have been externally insulated. The 300mm Neopor insulation has been fixed with an adhesive rather than using metal or plastic fixings that would compromise its thermal performance. A waterproof but vapour-permeable reinforced render from Sto has been applied as a final finish over the insulation.
- Other sustainable aspects include: 36sq m of photovoltaics to generate electricity; the presence of vacuum tube solar panels to provide about 70% of the hot water used; a mechanical ventilation heat recovery system; a wood burning stove; and a rainwater harvesting tank.
Original print headline - Zero Carbon House
Leeds Environmental Design Associates
RHF Heating Co
David Jones Electrical
Intello Plus airtight membrane
Ecological Building Products
Warmcell 500 insulation
Excel Industries Manufacturer
Vitral & Fakro
Triple glazed doors & windows
Rainwater reclamation pump
Rainwater Harvesting Systems
Solar roof panels
Glaster lime plaster
Reclaimed timber joinery
B-Clear honeycomb sandwich composite panels
External render insulation
Teplo thermally insulating wall ties
Sumatec clay blocks
Mechanical ventilation recovery system
Green Building Store
GFC Lighting; iGuzzini, Erco & Thorn
Rudders & Paynes
Roof insulation boarding
Natural Building Technologies