‘Weaker’ zero-carbon homes target outlined

Developers will have to achieve a minimum level of carbon reduction on the site of a housing development before off-site measures can be used to achieve zero-carbon status.

The Communities Department (DCLG) published a consultation on the definition of zero-carbon homes in December.¹ It had been expected in the summer, but issues over allowing housebuilders to count energy generated by off-site renewables complicated talks (ENDS Report 406, pp 10-11).

Last year, the UK Green Building Council (UKGBC), which represents the construction industry and several NGOs, warned that a definition of zero-carbon that did not allow some off-site energy generation was not achievable on up to 80% of new homes (ENDS Report 400, pp 4-5).

The DCLG has aimed to strike a balance between meeting green objectives and ensuring housebuilders can afford the policy, particularly given the housing downturn.

The consultation proposes a ‘carbon compliance level’ that builders will have to achieve on new homes. They will be able to reach the level through a combination of energy efficiency measures, on-site energy supply or connections to low-carbon heat.

It proposes using standards such as Germany’s PassivHaus standard to benchmark a home’s energy efficiency. Homes that meet this standard are typically 90% more energy efficient than the average existing home, because of good air tightness and insulation.

The government has suggested the carbon compliance level results in carbon emission reductions of 44-100% compared with today’s building regulations. The lower end of the scale would only be equivalent to code level 4, the carbon-reduction level developers should meet by 2013. This would cost developers at least £4,700 more per home, the government estimates.

The highest level considered in the consultation is a 100% reduction of regulated emissions - those from space heating, ventilation, hot water and fixed lighting - plus emissions from cooking and appliances. Combined, these would cut carbon emissions by 150-170% compared with today’s building regulations. But this would cost developers at least £20,000 more per home and is technically impossible for flats, the DCLG said.

The government concludes it would not be appropriate to set the carbon compliance level at the highest level. A 100% reduction in regulated emissions is "at the top end" of what is realistic, it says. The DCLG seems to favour a 70% carbon compliance level. This would cost about £9,900 per home and would be "an ambitious but technically realistic aim" for most homes.

Remaining emissions, including those from cooking and appliances not covered by building regulations, would need to be reduced via other approved measures, known as "allowable solutions". These include:

• Carbon compliance beyond the minimum standard (towards or all the way up to mitigating 100% of emissions).
• Installation of energy-efficient appliances or building control systems that reduce a home’s expected energy demand.
• Exportation of low-carbon or renewable heat (or cooling) from the development, or from a connected installation, to existing properties previously heated or cooled by fossil fuels.
• Connection of off-site renewable electricity to the development by a direct physical connection.
• Retrofitting existing homes near the development with energy-efficiency measures.