Zero carbon: Four for the price of three

This will have come as a relief to many. In 2006, when the target was set, it galvanized the industry and led to a spate of R&D projects aimed at finding ways to build zero-carbon homes.

Although Shapps’ confirmation suggests this work hasn’t gone to waste, there’s been little evidence of the mass roll-out of homes that meet any level of the Code for Sustainable Homes. And with the housing market still in the doldrums the appetite for investing in more low-energy prototypes isn’t likely to return soon.

Fortunately, a new project could provide much needed impetus. AIMC4 - Application of Innovative Materials, Products and Processes - has a clear goal: to pioneer the volume production of houses to the energy performance of level four of the code without the use of renewables - and for the cost of a level three house. This will come as good news to social housing providers as the Homes and Communities Agency is consulting on making level four compulsory for all homes that it funds from next April, two years earlier than it takes effect for all housing.

We need to be sure that you will be able to get a mortgage, and that future changes to the Building Regs won’t block it from the market

Ross Holleron, BRE

The idea is to focus on the performance of the building fabric. The crucial thing, though, is that the solutions that come out of the three-and-a-half year project must be suitable for mass-market application. The consortium behind AIMC4 includes the housebuilders Stewart Milne, Barratt and Crest Nicholson, which between them had about 17% of the total new-build housing market before the downturn and will be looking to use the solutions for future schemes. “Ultimately they will support the creation of mainstream zero-carbon homes,” says project leader Stewart Dalgarno.

The idea is to design and develop a minimum of 12 homes. These will be houses rather than apartments, partly because hitting level four using a fabric-first approach is extremely difficult with apartment buildings because of the dominance of domestic hot water in the energy use. “We’ll crack houses first to see what lessons we learn before moving to apartments,” says Ross Holleron, principal consultant with BRE which is providing technical and design evaluation.

There are a many technical hurdles to overcome. SAP 2009 - which is awaiting release from the communities department - will be used as the main assessment tool; the energy efficiency standards for zero-carbon homes set out by the Zero Carbon Hub have been adopted as a minimum. These are 46kWh/m2/year for semi-detached and detached homes and 39kWh/m2/year for all other homes. “That is a minimum and we firmly believe you can go beyond that. Arguably we are trying to achieve or better Passivhaus standard,” says Dalgarno.

The consortium is in the process of identifying the technologies that it hopes to adopt. Candidates include advanced timber frame, masonry and hybrid systems for the structure and envelope, as well as thinner and more efficient insulation materials, solutions to minimise thermal bridging and ways of achieving greater airtightness. One area of particular interest is party wall construction and achieving zero heat loss.

Technologies that improve domestic hot water efficiency and hybrid ventilation systems are also being targeted. “This is important because we are getting to and potentially beyond where investment in the fabric becomes sensible,” says Holleron.

Some technologies are already on the market, some are emerging and some are a way off but could do with accelerating through development. Because the 12 houses will be sold, the NHBC has been involved throughout the selection process to identify where there might be issues with certain materials or products and fast-track the approval of warranties.

Other stakeholders include mortgage lenders, the Association of British Insurers, planners and the communities department. “We need to be sure you will be able to get a mortgage or insure these properties,” says Holleron. “And that future changes to the Building Regs won’t block us from bringing it to market.”

Improvements in processes are also being made. Stewart Milne, for example, hopes to become one of the first housebuilders to fully exploit building information modelling (BIM) in the design process and eliminate errors and waste. “One of the attractive aspects of BIM is that you can build up a library of things such as 3D junction details for improved airtightness and thermal performance and then do a virtual fly-through with site operatives before getting on site.”

The other issue is cost. The three housebuilders pooled the detailed cost data they had on building to level three of the code to set a benchmark for the project. Dalgarno won’t give the exact figure but says it is slightly above the 4-7% increase above a conventional house quoted by Cyril Sweett in its cost review of the code. “It means we’ve got a real world cost and it includes additional factors such as prelim costs. I think we’re unlikely to hit the price point with the first 12 but we’ll have a good picture of what it will be when we come to exploit it in 2013.”

The first homes should be on site in March next year and once the properties are completed they will be sold to housing associations or tenants and then monitored by Oxford Brookes university for a year.

Between them the consortium members have contributed £3.2m towards the project, which has been matched by the Technology Strategy Board. A cost of £6.4m might seem like a lot to build 12 homes, but if they can mass-market the solutions, that number might soon be nearer 20,000.