Do housebuilders have to go into the red in order to turn green? It looks like they do, because putting in ecological features can be so expensive that payback times may never come.
When Part L of the Building Regulations comes into effect in April, its energy-efficiency measures will reduce the annual CO2 output of a house from 4.5 tonnes to 1.5 tonnes. Aside from the reduction in energy bills, the cut in CO2 emissions should give an environmental feelgood factor to every new home, and to every potential homebuyer who spends their Sunday morning dropping bottles into the bottle bank.

But homebuyers are unlikely to hear about the change. Most of the housebuilding industry sees the requirements of Part L purely in terms of the £600 to £1200 it will add to the build cost of a house. Few are able to exploit insulation, or other advanced green technology such as photovoltaic panels or water-saving devices, as a marketing opportunity that could attract buyers. "All the technology is available to make homes greener. It is a matter of breaking down the usual barriers," says Steve Prismall, director of SPD Architects.

For private housebuilders, every upgrading of the Building Regulations brings cost penalties, and green technology can face housebuilder opposition because of its sheer unfamiliarity to industry and consumers. "A lot of housebuilders lack expertise – how many have services consultants?" says Prismall. "Houses are designed for optimum space, not the efficiency of the hot water system, and it is cheap to put in another soil stack.

So you end up with complex plumbing systems where it takes a long time for the hot water to reach the tap – and with a water-saving tap the flow can be even worse."

For registered social landlords, energy- and water-saving technology can bring benefits for cash-strapped tenants in reducing running costs, but the Housing Corporation's grant allowance for going green is limited to a 1% supplement to the total cost indicators. The supplement would not be enough to buy a sizeable installation of photovoltaics for a house, as that would come in at about £5000 to £15,000, and housing associations do not have free rein in how they spend the supplement. In order to be eligible for the cash, homes must earn a "good" pass under BRE's EcoHomes environmental measurement system.

The Housing Corporation has set a target in its corporate plan for 70% of new-build social housing to achieve an EcoHomes rating of good by 2004. To help housing associations move towards that, the corporation is backing a special project called Sustainable Homes, which is carrying out research into the cost of going green. "Our preliminary information indicates that it will cost more to produce EcoHomes," says Jenny Wain, project co-ordinator for Sustainable Homes.

Just how much more depends on the shade of green of the housing. Go for high technology and you could encounter costs that won't be recovered within a lifetime. But greening doesn't have to cost that much more. Wain says: "RSLs that have built sustainable homes in the past five years have mainly done it within their social finance structure.You can make a house have a better environmental performance by spending 1-2% more."

Richard Baines, environmental consultant to housing association, Black Country Housing and Community Services Group, says: "The problem with green design is that people are always looking for the gizmos. Truly sustainable design is not about that."

All the technology is available to make homes greener. It is a matter of breaking down barriers

Steve Prismall, director, SPD Architects

Richard Hodkinson, head of environment consultant the Richard Hodkinson Consultancy, agrees. "The housebuilding industry could do a lot of straightforward things first – like putting in an energy-efficient boiler, which doesn't cost much more [see chart].

"There are particular things that could be attractive in the marketplace, although most housebuilders have not thought about marketing them," he adds.

Gleeson Homes has thought about it, however – it is planning to use the environmental performance of its homes as a selling point in its brochures. The company measures its schemes against 16 environmental key performance indicators, covering such areas as reuse of building materials, waste, water and energy use, and layout and planning. As a result, it routinely fits technology such as water-saving spray taps.

"If you procure the right sort of tap, the additional cost is negligible," says environmental manager Tom Whatling. The company commonly fits the Waterguard system in apartments, which monitors the incoming water supply and shuts it off in the event of a leak. The system costs about £120 a unit but provides an environmental benefit and peace of mind for residents.

Fitting that kind of technology is easy, says Whatling. "Things like rainwater harvesting are much harder. The technology is there, but it is not readily accepted in this country. The public can be sceptical of payback times."

Public acceptance of technology seems to be growing, however. When Laing Homes trialled photovoltaic panels on a private housing scheme in Edmonton, north London, it found that homes sold quickly, even with a £5000 price premium to help pay for them. "But I don't believe that people bought because the homes had photovoltaics," says Mark King, technical development manager with Laing Homes. "They bought because of the market."

At the end of last year, the government announced that it was providing £4m in grant aid to fit photovoltaic panels on 400 homes. Persimmon is set to benefit from that grant, and is working with solar panel producer Intersolar to develop six houses on a site in Clapham, Bedford. The roofs have Electra-Slate tiles, incorporating an embedded solar electric panel produced by Intersolar at a cost of about £14,000 a home, and the government grant will cover about half the additional cost. But the total bill for the solution is £17,000 a house, because for aesthetic reasons the solar tiles will have to be used alongside slate roof tiles, adding £2000 to the roof's cost, and electrical work comes in at a further £1000.