Zero carbon homes
The Climate Change Act was introduced in the UK in 2008, creating a long-term, legally-binding framework for tackling climate change. It set a target of reducing carbon emissions by 80% compared to 1990 levels by 2050, with a reduction of at least 34% by 2020. A strategy for how this was to be achieved was set out in The Carbon Plan published in December 2011.
In December 2006, the Labour government committed that from 2016 all new homes would be ‘zero carbon’ and introduced the Code for Sustainable Homes, a code against which the sustainability of new homes could be rated. This commitment was affirmed in the Building a Greener Future: Policy Statement 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.
The Labour budget in 2008 announced the government's intention that all new non-domestic buildings should also be zero carbon from 2019.
Whilst these were seen as bold commitments, there was scepticism about whether such ambitious targets could be met, as well as some confusion about what ‘zero carbon’ means.
The first definition of a zero carbon home was a home achieving Level 6 of the Code for Sustainable Homes. This included emissions of both regulated energy (space heating, hot water, lighting and ventilation) as well as unregulated energy (such as appliances and cooking).
In the 2011 budget, the coalition government confirmed the commitment that from 2016 all new homes would be zero carbon, however it excluded unregulated energy use from the definition.
In England, the current definition of a zero carbon home is one 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 ‘carbon compliance’ standards):
- 39 kWh/m^2/year for apartments and mid-terraced houses.
- 46 kWh/m^2/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)/m^2/year for detached houses.
- 11 kg CO2(eq)/m^2/year for attached houses.
- 14 kg CO2(eq)/m^2/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.
So in effect, developers will be required to avoid or mitigate all regulated emissions using a combination of on-site energy efficiency measures (such as insulation and low energy heating systems), on-site zero carbon technologies (such as solar panels) and off-site measures to deal with any remaining emissions.
What constitutes off-site ‘allowable solutions’ has yet to be finalised but it might include the developer making payments to an ‘allowable solutions provider' who could be a local authority provider or a private provider. There is also the possibility of creating a national carbon abatement fund. Payments might be made by means of an agreed fee per kg CO2 to offset emissions over a 30 year period.
On 8 July 2014, the government published its response to the summary of responses to its consultation on allowable solutions. This confirms the four approaches to allowable solutions for house builders; abatement on site, their own abatement off site, third party off-site abatement, or to payment into a price-capped fund. It also confirms that a national design framework will be established for the scheme.
In England, the requirement for zero carbon homes will be set out and enforced in the 2016 building regulations, specifically parts L (Conservation of Fuel and Power), F (Ventilation) and J (Heat Producing Appliances) and their approved documents.
A number of concerns remain with zero carbon homes:
- There is some concern that the standards will be watered down further before 2016.
- Typically, every year, new homes account for just 1% of the total housing stock, and at present it is considerably lower than this. This means that the proposed measures will take a long time to have a significant impact on total emissions from the UK building stock.
- Developers may decide it is easier and adopt ‘allowable solutions’ rather than meet the carbon compliance standards.
- It is questionable whether the standards really achieve 'zero carbon'. In particular, as with other standards such as BREEAM and LEED, they focus on operating emissions rather than capital emissions (ie they do not take account of carbon emissions resulting from actually constructing a new home).
- It is not clear how the long-term maintenance and any future alterations to new buildings will be regulated.
- There is some concern about the impact these measures will have on the pressing need for more new homes as the UK population increases, as well as how this necessary increase in housing stock will affect the UK's ability to meet overall emission targets.
- Questions remain about measures to deal with the difference between the predicted and actual energy performance of buildings which can be significant. Measures might include publishing a standard Publicly Available Specification (PAS) or code of practice.
- There is concern about whether the time-frame for change is realistic.
The Infrastructure Bill published by the Department for Transport on 6 June 2014 proposed setting the zero-carbon home standard at Level 5 of the Code for Sustainable Homes, but permitting developers to build to Level 4 by using allowable solutions to achieve Level 5.
However, controversially and unexpectedly it also proposed exempting small sites from allowable solutions requirements. There was no definition of what constitutes ‘small sites’, although on 17 July 2014, DLCG minister Lord Ahmad suggested it might be similar to the 10-homes exemption already proposed for Section 106 agreements (ref Today's House of Lords debates - Thursday 17 July 2014). This is seen by some to introduce a significant loophole.
A consultation on the proposed exemption was launched on 18 November 2014. Ref DCLG Next steps to zero carbon homes: small sites exemption. On 27 March 2015, the government published its response to the consultation, confirming that sites of 10 units or fewer or a maximum size of 1000 square metres of floor space will be exempt from the allowable-solutions element of the zero-carbon homes standard.
 Find out more
 Related articles on Designing Buildings Wiki
- Allowable solutions.
- Code for Sustainable Homes.
- Domestic micro-generation.
- Eco towns.
- Emission rates.
- Energy Act.
- Energy performance certificates.
- Fabric first.
- Green Deal.
- Home Quality Mark.
- Performance gap.
- PV inverter.
- Renewable energy.
- Sustainable materials.
- The Future of Electricity in Domestic Buildings.
- Zero carbon non-domestic buildings.
 External references
- Zero Carbon Hub: Low Carbon Buildings and Homes, Skills and Opportunities, Phase 1 Report.
- The Zero Carbon Hub: Zero carbon homes.
- Building Regulations Part L 2013 Consultation.
- The Energy Act 2011.
- The Carbon Plan.
- The Planning Portal: Code for Sustainable Homes.
- Zero carbon compendium: Who's doing what in housing worldwide.
- CLG: Open consultation: Next steps to zero carbon homes: allowable solutions. August 2013.
- Zero Carbon Hub: Zero Carbon Strategies for Low and Zero Carbon Homes|.
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