Housing minister Grant Shapps has promised to pin down the definition of zero carbon development within weeks. It couldn't come too soon.

Nearly four years ago, the then Labour government began to consider a bold move, a step into the unknown. There had been talk for some time about a low-carbon economy, but ministers were keen to translate this into something more concrete. The idea of zero-carbon development took shape.

Then, in 2007, the government opted to do something very ambitious indeed. It decided that from 2016, all new housing built in the UK must achieve a zero-carbon standard. Social housing is supposed to meet that goal 12 months earlier.

But despite years of consultation, an accepted definition of what is meant by zero carbon remains elusive. That frustrating state of affairs should be about to change.

Last month, Grant Shapps, the housing minister in the new coalition government, said the new administration was 100 per cent behind the target, and the similar ambition for non-domestic buildings from 2019.

He said: "The last government was right to set us on this journey. But 2016 is not far away, and industry needs to know what it needs to do to design and build zero-carbon homes. So after four years of consultation, it is time to finalise the definition of zero carbon. I intend to do that within the coming weeks. Finalising the definition will be the end of the beginning. The next step is for our partners to turn policy into reality, with government stepping back so that industry can develop the solutions the country needs."

Amen, says the industry and energy providers. How the definition is framed will have an impact not just on how buildings are made but also on the deployment and take up of a whole range of green energy systems: photovoltaic solar panels, heat pumps, biomass boilers and so on.

Last month, the biggest ever survey of the UK development industry found that three-quarters of respondents thought the government's current zero-carbon targets for the sector unrealistic.

Liz Pearce, chief executive of the British Property Federation, says: "With an industry that is sceptical about carbon reduction targets, closer collaboration between government and the industry is essential if these are to be met. Government will need to work with all sectors to understand fragmented views and identify why certain sectors feel the targets are more achievable than others."

Nailing down the zero carbon definition might just help to steady some nerves.

*Site specifics: how the HCA is pioneering the development of zero-carbon social housing*

The Homes and Communities Agency (HCA) is the national housing and regeneration delivery agency for England. Its role is to create thriving communities and affordable homes. It is closely involved with pioneering examples of zero-carbon housing development, as well as monitoring how carbon compliant these early schemes are in practice.

The most ambitious scheme the HCA is involved with is Hanham Hall in south Gloucestershire. The project is part of the HCA's Carbon Challenge programme, which provides HCA land to developments. It is the first large-scale housing scheme designed to meet Level 6 of the Code for Sustainable Homes (which effectively equates with a zero-carbon development) in England. A total of 195 homes are being developed, on a former hospital site, by a consortium led by Barratt Developments in partnership with Arup, Kingspan Offsite and Sovereign Housing Group. The homes, designed by HTA architects, are due for completion next year. The scheme will include rainwater harvesting, orchards, a car club, district biomass combined heat and power, community trust and refurbishment of the original Grade II listed building.

Another project of interest is at Upton, Northampton. Here, there are six completed and inhabited Level 6, three-bedroomed homes, developed by Metropolitan Housing Partnership with HCA funding. The homes include community-scale wood pellet boilers, green roofs, rainwater harvesting, roof-mounted wind cowls, a composting system, solar photovoltaics and thermal panels. Sensors have been installed in three of the properties to monitor energy consumption and generation (which can be sold back to the grid), and the developer is working with the University of Northampton to analyse the information.

A third scheme, called Parkdale, is under way at Fryston, near Wakefield. This is a development of 91 social homes being built by Willmott Dixon Group. Work started on site in March. The scheme received HCA funding from its National Affordable Housing Programme. It involves Level 6 homes built using traditional methods, with increased attention to detail and insulation. The homes will be connected to a small biomass combined heat and power system on site to meet zero-carbon requirements. A feature of this development is that each home will have its own individual greywater recycling system and low flow water appliances. The project is due to be completed by the end of next year.

*How to define a zero-carbon home*

A typical, average-sized house built to 2006 Building Regulations releases just over three tonnes of carbon dioxide a year. This figure is the sum of the carbon emissions from a building's regulated and unregulated energy use. Regulated energy use is space and water heating, and lighting. Unregulated energy use is that consumed by the home's occupants through activities such as cooking, watching television and using electrical gadgets.

The government has decided that from 2016 to achieve zero carbon, emissions from both regulated and unregulated components must total zero. It has also decided that 70 per cent of regulated emissions must be offset on site. This is known as "carbon compliance". The rest can be achieved by "allowable" solutions. What will be allowable is currently the subject of frenzied debate.

These allowable solutions could give housebuilders massive leeway in how they meet the standard because they do not necessarily mean fitting technology directly to individual homes. The target could be met by fitting a district heating system. There might be a large wind turbine in the fields behind the house or a set of photovoltaic panels added to the school and doctor's surgery down the road. More ambitiously, the housebuilder might pay for some of the surrounding houses to be retrofitted with green technologies, so the carbon emissions saved by them compensates for the extra carbon emissions of the new homes.

Even more controversially, a developer could invest in a windfarm in Scotland to balance the emissions from a new housing estate in Surrey. What just about everyone agrees is that these allowable solutions will be tough to administer, police and measure, which is why the consultation has taken so long.