Britain's greenest architect is trying to turn BedZED, his first zero-energy housing scheme, into a financially viable product. So the new, improved model comes in a box – complete with a team to build it for you.
Architect Bill Dunster is going to make building an eco-friendly home as easy as buying a car. He has taken his carbon-neutral BedZED development in Sutton, south London and turned it into an off-the-shelf package called ZED in a Box, courtesy of his company ZEDfactory. Not only do developers get a complete kit of parts to build a ZED (zero-energy development), but they also get a project team to build it for a guaranteed maximum price. All the developer has to do is pick up the phone and make a call. Just like a salesman, Dunster patters: "It's ever so easy and convenient to go green – you won't even have to think about it." The only thing is, developers do not want to build ZED in a Box homes. Much to Dunster's disgust, conventional housebuilders have rejected the ZED concept. "The housebuilders just don't believe in it. They open their electric garage doors, jump into the Jag and chain-smoke their way to the board meeting," he splutters. "Why would they embrace it? It's a complete culture change. They design their products to the lowest common denominator that offends nobody."

Because of this attitude from the housebuilders, Dunster has had to think of a novel way of getting the ZED in a Box concept off the ground.

The first hurdle was making it a predictable financial bet. The problem is that lenders don't like anything out of the ordinary. "We can't get anyone with conventional access to large sums of money to fund schemes because the big financial institutions are very risk averse," says Dunster. This rules out housebuilders and developers, but still leaves housing associations, local authorities and private individuals as a potential market as they have alternative sources of funding. However, this group still needed convincing that a ZED development was a viable proposition.

The answer was to package the whole solution up to give cost certainty. Dunster has come up with five standard house types and three live–work units. Each is broken down into a list of 26 components in order of build process for building a ZED – for example the first, A, is the substructure, P is the plumbing and Y the landscaping. Within each component there is a green build specification fulfilled by specific products with prenegotiated prices. Consultants with standard fees are lined up, and Dunster has negotiated a guaranteed maximum price with contractor Miller Construction for £5m-plus developments, a major step forward. "Contractors' risk pricing was what made BedZED so damn difficult," remembers Dunster. "Risk pricing is a really big deal." This means every single component of a ZED home can be accurately costed.

ZEDfactory has developed a neat spreadsheet program that clearly appraises the viability of a project. All the cost data for a project is entered and it comes up with a total cost for the project and even the residual land value – the land value with a specific development on it. "You can change the price of a wall tie and you can immediately see how it affects the residual land value," enthuses Dunster. The program also means the specification can be altered to make a scheme more affordable – for example, the sewage treatment plant can be taken out to make a scheme initially affordable, and it can always be added back later. All this information even translates into an ordering schedule.

Dunster's meticulous approach has won over enthusiastic supporters. "This has enabled Bill to leapfrog from a superb but isolated landmark project to an incredibly sophisticated development concept," reckons Adrian Hewitt, the principal environment officer for the London Borough of Merton, who is working on a ZED for the borough. "People are now able to think about a ZED with their heads rather than their hearts." Hewitt thinks the computer program is central to the success of the concept. "What really persuaded us was the computer modelling system; this was the key thing as it gave us the sense of security this was going to work."

Dunster has also come up with a novel procurement method to reach private buyers. Because ZED in a Box is a complete package, Dunster reckons he can bypass the housebuilders. BedZED has enjoyed enormous publicity and has generated a long list of keen buyers on the ZEDfactory website. "We have 500 people who want a ZED home, but can't get one as there are none on the market," Dunster explains. If there are enough people in an area to make a development viable and a site can be found, the potential buyers can form a development company and fund the homes with self-build mortgages. The other alternative is to pre-sell offplan to buyers – but the lack of conventional funding will mean there will not be any speculative ZEDs.

Housing associations are another key market. "We are very much hoping housing associations will take up this offer as they are committed to the same values. They will be more interested as we have done the value engineering and the risk is taken out," says Dunster. And there is more good news. "The Housing Corporation is actually listening – this is a real breakthrough," says Dunster. They are paying for the distribution of a ZED in a Box information document that will be made available to every housing association in the country.

Dunster has had to work hard to overcome a second obstacle. A ZED will cost more to build than a conventional development. But Dunster hopes that with the ZED's green credentials he can negotiate higher densities to offset higher construction costs. This is where the spreadsheet tool comes in handy, as, unusually, it enables planners to see how a ZED stacks up financially. "It allows for completely open-book negotiation," Dunster explains. "It diffuses the hostility between the planners and the project team."

All Dunster's hard work looks as if it is finally paying off. He has secured a site near Cambridge for a 30-unit self-build financed scheme and is working with the London Borough of Merton on a 260-unit development called MorZED that will be partly housing association, pre-sold to private buyers and possibly self-build. Work is also due to start on an 11-unit sheltered housing development for Accord Housing Association in Dudley, near Birmingham.

And it looks as if the generally negative attitude to green housing developments could be about to change – at least at local government level. Under Ken Livingston's draft London Plan, every London borough has to have a zero carbon development by 2010. Merton has undertaken a feasibility study document based on the ZED in a Box concept to assist local authorities in reaching that target. All of which should help promote the ZED concept.

In the long term, Dunster reckons he can undercut the volume housebuilders as ZED homes do not need heating systems, which are expensive to install. "As we gain economies of scale with the ZED supply chain, we won't need the planning gain – we will be producing cheaper buildings because there are no services in them," he explains.

If all goes to plan, it will only take one or two commercially successful ZED in a Box schemes before housebuilders start tripping over themselves to get in on the act.

Green and greener: How the BedZED concept has evolved

The original BedZED, built for the Peabody Trust housing association in 2001, featured 82 south-facing terraced homes and 1600 m2 of work space. In the daytime, solar gain from full height conservatories heats up the concrete structure and that heat is released through the night. Because the homes are so well insulated there is no need for a heating system. Electricity and hot water are provided by a combined heat and power plant burning waste wood from tree trimmings, which is supplemented by solar panels. The ZED in a Box concept is virtually identical in concept, but has been tweaked to make it easier to build and to live in. One big change is substituting blocks for hollow core planks to construct the inner leaf of the cavity walls. This allows ducting for the heat recovery ventilation system to be run inside the plank cores, eliminating expensive sound- and fire-insulated ducting. This prefabricated solution means the homes will be faster and cheaper to build – and will qualify for grants such as the Challenge Fund, set up to promote homes built using off-site manufacturing techniques. There is a plethora of minor improvements too. For example, the windows will be supplied complete with the window casing to cut down on-site construction time, and the airing cupboard will come as a unit complete with pre-plumbed hot water tank and meter cupboard. Feedback from BedZED residents has been incorporated too. Thick walls and triple glazing mean the houses are very quiet inside so people become more aware of internal noise. There will be better sound insulation between floors, and the squeaky wind cowls used for the stack ventilation system will be fixed. “It’s relative trivia, but it is important to people,” comments Dunster.