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Asked to speak on whether the mainstream zero-carbon home would ever happen at last month鈥檚 Ecobuild conference, my thoughts went immediately to what the definition of a zero-carbon home is, and then to how this target came about. As it stands, the government is currently consulting on exemptions from zero-carbon targets for small sites, as well as 鈥渁llowable solutions鈥� (which would allow housebuilders to offset carbon developments off site), but there is a long history of debate around the definition.

In December 2006, the Labour government committed to the target that from 2016 all new homes would be zero carbon, also introducing the Code for Sustainable Homes (CfSH) - a code against which the sustainability of new homes could be rated. This pledge was affirmed in the 鈥満诙瓷缜� a greener future policy statement鈥� in 2007, which proposed progressive tightening of the building regulations to achieve the 2016 goal - first by 25% in 2010 and then by 44% in 2013. Next came the Climate Change Act which was introduced in the UK in 2008, creating a long-term, legally binding framework for tackling climate change which was further defined in The Carbon Plan strategy, published in December 2011.

Despite almost a decade of legislation and targets focusing on the zero-carbon home, the definition is still being debated. Originally thought to be a home achieving Level 6 of CfSH, this definition was changed in the 2011 Budget, when the coalition government reaffirmed the post-2016 commitment. The current definition is a home where CO2 emissions from regulated energy use are limited or mitigated by a combination of three factors (the first two of which are known as 鈥渃arbon compliance鈥� standards):

1) Achieving minimum Fabric Energy Efficiency Standards based on space heating and cooling:

• 39 kWh/m2/year for apartments and mid-terraced houses
• 46 kWh/m2/year for end of terrace, semi-detached and detached houses

2) Using low and zero-carbon technologies and connected heat networks to limit on site built emissions:

• 10 kg CO2(eq)/m2/year for detached houses
• 11 kg CO2(eq)/m2/year for attached houses
• 14 kg CO2(eq)/m2/year for low-rise apartments

3) Where it is not possible to reduce the regulated CO2 emissions to zero using these on-site measures, the remaining carbon emissions can be mitigated through allowable off-site solutions. What constitutes these 鈥渁llowable solutions鈥� has yet to be finalised, but it may involve the developer making payments of a certain amount per tonne of CO2 over a 30-year period.

What is becoming increasingly clear is that the specification and design of our new homes will vary depending on who wins the election. The current government favours building regulations and the definition of a zero-carbon home will depend on the final Part L Approved Document. Having said this, we have had indications that the final definition could be similar to Level 4 of CfSH, with the option of all additional carbon being offset through allowable solutions. Meanwhile, Labour stated in their manifesto that they would revert back to the definition proposed in 2011, although they have not been clear on whether this includes regulated energy (heating, lighting and ventilation) only.

New homes account for just 1% of total housing, so it might be prudent for the new government to turn their attention to improving existing housing stock

Whatever the outcome of the election, as an industry we need to consider what new technologies will be required if we wish to achieve zero-carbon homes through construction. There are so many questions that need to be answered ahead of 2016. For example: will we be manufacturing more products off site in factory conditions, such as windows with air tape barriers so that we can guarantee achieving air leakage targets? How will new technologies such as solar hot water, biomass, photovoltaics, mechanical ventilation systems and district heating systems stand the test of time? What is the cost to the end user? Will manufacturers and home builders invest in zero-carbon innovation? And will we design for future upgrading? Alternatively, would it be acceptable for volume to be achieved through offsetting?

It鈥檚 also worth considering that the required standards could be watered down further before 2016, particularly as political pressure increases to build more homes at affordable values in order to meet demand. Equally, current plans do not take into consideration how long-term maintenance or any future alterations to new buildings will be monitored. Interestingly, new homes account for just 1% of the total housing stock, so it might be prudent for the new government to reconsider the overall impact new homes will have on carbon emissions and turn their attention to improving existing housing stock.

Will the mainstream zero-carbon home happen? At Ecobuild, my fellow speakers and I concluded that it would not be achieved through construction methods by 2016 and that the eventual solution would almost certainly require allowable solutions.

Debbie Aplin is managing director of Crest Nicholson Regeneration