Friday04 September 2015

John Christophers’ Zero Carbon House

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A home in Birmingham’s Balsall Heath is the first retrofit project to achieve level 6 of the Code for Sustainable Homes

John Christophers
Balsall Heath, Birmingham
November 2009

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.

Extension with original Victorian element to its right.

Credit: Martine Hamilton Knight/Sto External wall insulation systems

Extension with original Victorian element to its right.

“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.

Top-lit radiating stair with treads made from reclaimed timber.

Credit: Martine Hamilton Knight/Sto External wall insulation systems

Top-lit radiating stair with treads made from reclaimed timber.

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


Project team

Environmental engineer
Leeds Environmental Design Associates
Main contractor
Speller Metcalfe
Structural engineer
Shire Consulting
Mechanical subcontractor
RHF Heating Co
Electrical sub-contractor
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
Greenshop Solar
Glaster lime plaster
Classic Joinery
Reclaimed timber joinery
Gallande Joinery
Williams Ironmongery
B-Clear honeycomb sandwich composite panels
Neopor insulation
External render insulation
Teplo thermally insulating wall ties
Sumatec clay blocks
Mechanical ventilation recovery system
Green Building Store
Light fittings
GFC Lighting; iGuzzini, Erco & Thorn
Rudders & Paynes
Roof insulation boarding
Natural Building Technologies


Readers' comments (9)

  • old is gold

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  • No NIMBY`s in that street it would seem!

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  • the last time i checked, a retro fit is in improve only the existing fabric, not to encase a building on 3 sides with an eco hat twice in size.

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  • nice one, the elephant in the room for energy reduction is old housing stock, making these buildings fit for the 21st century is imperitive. this is the way forward, and it's good to see someone going for it imaginatively

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  • first eco-build I have seen that has done something interesting with the architecture - well done

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  • Fantastic Regeneration! Is there any specific case study for tower building regeneration? Cheers

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  • According to my back-of-envelope calculation, uprating a solid brick wall to a U value of 0.11 with insulation k value 0.04 will take an insulation thickness of 350mm. Have I got that right? It would be an awful lot of floor space to loose to internal lining if you were not extending the property.

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  • R Sage: We overclad the existing and new masonry externally, on the sides and rear, with 280mm "Neopor" rendered insulation. So there is no loss of floor space at all there.
    Just on the old front elevation there is a 350mm depth of insulation (internal cellulose dry lining) where we do loose some floorspace, but we gave new window seats and splayed reveals to the old openings, and opened up the roofspace, so there are also compensating gains to the design. If the loss of floorspace in that one area had been a problem, we would have looked at a higher performing insulation for this one area - ie aerogel etc - but it wasn't an issue.

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  • I congratulate the team for reaching such a high level performance particularly when starting with a house that performs so poorly. That is indeed an achievement. Architecturally however, I struggle to see how the new portion complements the old. There is a danger that projects like this undermine the attempts being made to reconcile conservation with a low carbon agenda. I also have to question how true the build cost is or at least what has been included. Is this material cost only and have all the labour costs been taken into account.

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