We need to reach an understanding of what we mean by a zero-carbon home. Until then, the debate will continue to be governed by politics and hot air

Sometimes you hear something so patently outrageous that it makes you splutter and wince in sheer disbelief. An example might be Boris Johnson running for London mayor. One man I would not normally associate with the frivolous or outlandish is Gordon Brown. Yet just before becoming prime minister, he made an announcement on housing policy that had me almost choking on my soup.

Brown says he wants five new “eco- towns” to be created and he wants the 100,000 homes in “carbon-neutral” communities to be built on old industrial sites. All this by 2016.

Let me be clear: the need to reduce our reliance on fossil fuels and maintain more sustainable lifestyles is a given. Indeed, last year the Code for Sustainable Homes was introduced to gradually move housebuilders towards adopting a very low, carbon-neutral or zero-carbon development practice. Although not trumpeted by the sustainability lobby as epoch-making, the code has been designed to help the UK reach its sustainability targets. It has a sliding scale of levels, with the holy grail of level six expected to be the norm for developers by 2016.

There are a number of low or zero-carbon developments already built in the UK and overseas from which we may learn. BedZed in Sutton was one of the earliest pioneers of sustainable development and a low-carbon lifestyle. Despite some of the early problems it encountered with embryonic biomass technology, it has proved to be an effective way of housebuilding.

However, developers increasingly face a desire by planning authorities and public agencies to impose a minimum of code level three if they are to gain planning approval. This is much more rigorous than has been previously required, meaning that costs have risen to provide for the mandatory minimum standards for energy and water use. Not surprisingly, profit margins have fallen. This is not encouraging housebuilders to adopt the new “voluntary” regulations with enthusiasm.

In December 2006, stamp duty exemption was announced for zero-carbon homes built between October 2007 and September 2012. Although this recognises the additional investment required by developers, the definitions referred to in the draft detailing the eligibility criteria, including that referring to zero carbon, are incompatible with the compliance requirements for the Code for Sustainable Homes – not very helpful.

Constructing a property to use the appropriate water and energy levels is one thing – achieving zero carbon is another

Clearly residential developers have not struggled to make decent profits in recent years, but this code, now affecting planning consent on an increasing number of projects, was supposed to have been a voluntary measure until at least April 2008.

Furthermore, we are increasingly finding public bodies with political agendas leaping to impose code levels five and six. These levels were set as an aspiration for the year 2016, when our knowledge of zero-carbon construction techniques would have progressed. To say they are jumping the gun is an understatement. Brown’s policy announcement has helped foster this over-enthusiasm among those apparently wishing to parade their new political credentials.

The difficulty with achieving the PM’s objective comes with the definition of zero carbon. A zero-carbon home (according to the code’s definition) achieves zero net emissions of CO2 from all energy use in the home, including televisions, kitchen appliances, stereos, mobile phones and computers. The experts say energy use can be difficult to predict in design and usually low-voltage loads are based on benchmarking best practice. Constructing the property to use the appropriate water and energy levels is one thing – achieving zero carbon is another.

A report from the Energy Saving Trust called, rather catchily, The Ampere Strikes Back, states: “By 2010 the consumer electronics sector will be the biggest user of domestic electricity, overtaking the traditionally high-consuming sectors of cold appliances and lighting.” Few of the people watching the recent Live Earth concert will have realised that the flatscreen televisions on which they viewed the rock spectacular were using three times as much power as the standard cathode ray tube TV sets. A case of a domestic appliance not becoming more energy-efficient as technology evolves.

What we need is a more cohesive and progressive carbon strategy if we are to achieve carbon neutral construction. So when there is talk of zero-carbon developments, let us reach an understanding of what is really achievable and take a pragmatic approach to implementation. Let us not be guided by the political hue of the day.