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Carbon Challenge: How to build a Level 6 house

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Hattie Hartman looks at two government-backed testing grounds for super-green housing

By 2012, all new-build housing must reach Level 6 of the Code for Sustainable Homes. But what would it be like to live in a Level 6 house? What does a zero-carbon home cost? These are the questions that Carbon Challenge, a testing framework for the deliverability, buildability, and marketability of zero-carbon housing and community projects, is meant to answer.

Carbon Challenge was initiated in 2007 by English Partnerships, and is now administered by the Homes and Communities Agency (HCA). Four projects are in the pipeline, two with architect-developer teams already in place. Barratt Homes’ Hanham Hall near Bristol was submitted for planning by HTA Architects in December 2008 with approval anticipated this spring, and Peterborough South Bank Phase One, by Browne Smith Baker for the pPod Consortium, is currently out for consultation.

The announcement of a preferred bidder for a third site in Doncaster is imminent, according to HCA project manager Jayne Lomas, while at the fourth site near Wigan, the HCA will carry out enabling works prior to offering the site to development teams.

Barratt Homes confirmed that the project is weathering the recession, though Hanham Hall is slightly behind the original 2007 timescale, due to additional time required for design and consultation.HTA wants to move away
from the idea of sustainability as a limitation and promote it as the good life. ‘We want to make green homes fly off the shelves,’ says HTA managing director Ben Derbyshire. Similarly, the Peterborough team started with a ‘blank slate’ brief to develop an appealing community for families.

Along with creating attractive homes, the developers are trying to keep down costs. Martin Edmunds of Morris Homes says: ‘The build cost is likely to be about 40 per cent more than a conventional house, but the homes will not be more expensive to purchase because we are advised that buyers are unlikely to pay a “green premium” in the current climate.’

The main lesson to date from the Carbon Challenge is that working to Code Level 6 is unduly restrictive. Warren Barnett, director of Browne Smith Baker, is adamant: ‘We should stick with Code Level 5 because you don’t have to be so prescriptive about the heat loss parameters and you can have more glazing and articulation.’ Rory Bergin, head of sustainability and innovation at HTA, agrees: ‘Code Level 6 leaves you no flexibility. You have to do everything in spades to meet the code.’

Hanham Hall

Location Bristol
Architect HTA Architects
Client Barratt Homes with Sovereign Housing Association
Units 195 units, 33 per cent affordable
Status Awaiting planning approval
Start on site Late 2009 to early 2010

The Bristol site encompasses the Grade II*-listed Hanham Hall, which will be refurbished for community use. The choice of a centralised district heating system means that the houses are not bound by orientation, according to HTA’s Ben Derbyshire. Powered either by biomass or biomethane, the system will export excess heat to an adjacent NHS facility (and doctors’ surgery) and sell excess electricity to the national grid. Grid connections to the adjacent buildings will be constructed simultaneously with the site infrastructure, though plans to export to a nearby school had to be abandoned for cost reasons. Barratt Homes acknowledges that some heat dumping is inevitable during summer.

House designs were modelled three times (this is typically done once), with input from Arup and Kingspan to maintain maximum daylight while achieving target U-values. The units were deliberately designed to accommodate a variety of solar orientations.

Ben Derbyshire, managing director HTA

This is an extraordinary time to create a new community. The huge perturbations of global markets have produced an awareness of the need to rethink society’s ambitions, and the Carbon Challenge programme provides an opportunity to explore the impact of regulatory changes on design. We were keen to explore how these changes impact the public. All our homes provide for indoor-outdoor living: they are not passive, sealed houses. The project promotes and nurtures the concept of collective living through the careful design of shared outdoor space and the provision of communal activities. We have looked at sustainable placemaking through the eyes of the consumer to find ways to make a zero-carbon lifestyle more attractive than alternatives on offer.

To see floor plans of the cottages in the Hanham Hall development, visit Hattie Hartman’s sustainability blog at www.ajfootprint.com

South Bank Phase one

Location Peterborough
Architect Browne Smith Baker
Client pPod Consortium (a partnership of Morris Homes, Gentoo Group and Browne Smith Baker)
Units 344 units, 35 per cent affordable
Anticipated start on site 2010

The Peterborough design team started by interviewing residents in nearby neighbourhoods to develop 15 typical households that were used as a basis for the house types. A well-considered masterplan creates a green zone along the railway line at the northern site boundary, and vehicular and pedestrian movement ties new streets into the existing fabric. A four-storey block of flats and an energy centre mark the main entrance.

The energy centre will house a CHP system powered by anaerobic digestion (AD), which generates power from local food waste or feed stock through the creation of a methane-rich biogas stored inside huge tanks. The biogas is then burned to generate heat and electricity. Anaerobic digestion was selected over biomass because of its more secure supply chain and long-term affordability. For the houses, the required wall U-value of 0.12W/m2K is achieved by a bespoke timber panel system, which can be either rendered or clad in timber or brick.

Warren Barnett, director Browne Smith Baker

At Peterborough, the client and design team were determined to produce houses that were both at the cutting edge of low-carbon emissions and readily identifiable as family homes. Floorplates based on the HCA performance specification were rigorously reviewed for ‘liveability’ and bench-marked against our profiles developed through on-site market research. With solid-to-void relationships and plans determined via careful analysis of the heat loss parameters, balanced against the performance criteria of the MMC system, basic ‘house’ armatures were dressed according to context within the transect of the masterplan and their physical orientation within the urban pattern on the site. All units have correctly proportioned outdoor space to promote family living.

The AD CHP plant eliminates the need to adorn the units with green bling. Surplus energy from the plant will be used in greenhouses, the community hall, creche and spa. A self-funding Community Interest Company will administer the grounds, run a car club and manage the community hall, creche and spa.

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