Builders seek to broaden ‘zero carbon’ definition

The building industry is seeking to broaden the definition of ‘zero carbon’ to include off-site generation and allow more flexibility in meeting government targets. But it has yet to decide on the issue of embodied carbon.

The definition of ‘zero carbon’ needs to be changed to allow builders more flexibility to meet targets, according to a construction industry group. The government wants three million homes built by 2020, with all those built after 2016 to be zero carbon.

Zero carbon was originally defined by the Communities Department (DCLG) in the technical guidance of the Code for Sustainable Homes last year. This stated that off-site renewables could be counted in mitigating homes’ carbon emissions.

But the Treasury came up with a different definition in its stamp duty land tax relief scheme, stating that off-site renewables would not be considered unless they were connected to the development by private wire. The DCLG then brought its definition into line.

Housebuilders complained the new definition was unworkable, leading the UK Green Building Council (UKGBC) to set up a task group to find a solution. This included Barratt Developments, Arup, BRE, Crest Nicholson, Lend Lease, the Renewable Energy Association, DCLG, the Business Department (BERR) and the Treasury.

The study found the current definition of zero carbon is not achievable on up to 80% of new homes.

To qualify all new buildings should first meet strict minimum energy efficiency standards, the group said, both in terms of the building design and household appliances, if supplied by developers. Carbon emissions should be mitigated on or near the development. Where this is not possible, a minimum level of carbon mitigation must be met on or near the site.

Above this, the UKGBC suggested off-site technology could be allowed if it has been built specifically to deliver the development’s energy needs. Alternatively the developer could pay into a fund to pay for new installations. The price of paying into this should incentivise the installation of on- or near-site measures first, it said.

UKGBC chief executive Paul King stressed the council’s recommended definition was not about abandoning the concept of zero carbon, but allowing developers more flexibility in how they deliver the number of homes needed. "Our proposed definition recognises that off-site renewables could play a part, and also gives a big boost to community-scale technologies."

This would also enable the distribution of zero- or low-carbon heat through district networks, which would lead to carbon reductions in the current stock, he added.

The government will formally consult on a definition for zero-carbon this summer. It also wants zero-carbon schools from 2016, zero-carbon public buildings from 2018, and all other non-domestic buildings to be zero carbon from 2019.

Although the UKGBC report concentrated on domestic buildings, the task group recommended the same principles should apply to the non-domestic sector.

The study did not consider embodied carbon in building materials. Mr King called the concept an "important dimension", but said it needs more work. Construction professionals are already raising concerns over this decision. Fifty organisations including Simons Design, Arup, Sheppard Robson, Construction Industry Research and Information Association, BRE and the government’s Waste and Resources Action Programme have formed a group - Construction Emissions Community of Practice - to take a holistic view of a building’s life from design to disposal.

The group hopes to tie their investigations in with the UKGBC’s future work. Rosi Fieldson, senior project architect at Simons Design, said the more technologies that are put into a building to make it zero carbon, the higher the embodied carbon becomes.

Currently, embodied energy comprises about 15% of energy used over a building’s lifetime. In buildings that are 30-40% better than current building regulations, the embodied carbon comprises 40-60% of the building’s energy over its lifetime. In a zero-carbon home, this would rise to 80-90%, Dr Fieldson said.

"We need to question whether getting to zero carbon is counterproductive," she said. To lower carbon emissions all round, a balance is needed between a building’s embodied carbon and the carbon emitted during it use. Embodied carbon can be reduced by changing construction materials but this must be considered at the design stage, she added.