Zero Carbon Homes as defined by the Code for Sustainable Homes

Our built environment accounts for over half of our carbon dioxide emissions. We now have the Code for Sustainable Homes (CSH) to help designers and builders of new homes in the UK. But will it help or hinder? In April 2008 the government launched the Code for Sustainable Homes (CSH), calling it a 'step-change in sustainable home building practice'. The scheme that it replaced, and that it is modelled on (EcoHomes) failed to capture the imagination of the very conservative house building industry outside token projects, that were blessed with government funding and housing associations. Unlike EcoHomes though, the CSH feels much more like a mandatory, rather than an optional code. In fact they did a lot more than that because at the political level, at the time of its introduction, we were at the pinnacle of a housing boom, with massive demand for homes and a lot of potential new housing sites hanging in the balance.

The government used this almost unprec­edented demand to throw down the challenge. Permission would be given for new sites as the incentive (new eco towns), but adoption of the CSH is the mandatory side. Essentially, the feeling was that any volume builder, who could prove to be singing from the 'zero carbon home' song sheet, could expect to be favoured with easier planning permission. It sounded good for the shareholders, good news for home buyers and good news for the environment. But is it?

Well the answer has to be a guarded 'yes' because it has captured the imagination of many mainstream developers and the industry as a whole. However, on the downside, since the launch of the CSH we have seen unprec­edented levels of greenwashing. The most striking example is that many, very ordinary building products are being re-branded green, purely based on the assumption that they could be used in projects built to the CSH stand­ards. No Code level is mentioned but let's not forget that Code level 1 is barely better than current Building Regulations! Another example is industry trade groups claiming that all their members are now zero carbon but merely on the back of carbon offsetting! Are they now CSH compliant?

The true definition of 'zero carbon' has yet to be properly defined and big players in the industry have recently discovered that they may have bitten off more than they can chew by going along with the government's rallying cry of 'zero carbon by 2016'. This is an impossible goal and doomed to failure from the beginning, but we need to watch this space over the next couple of years for a further re-definition and a probable watering down of what 'zero carbon' actually means. For the time being though see the table below for the present definition. One concern is that it will get diluted in its requirements but not in name. For instance, there is a proposal on the table suggesting that builders who are unable to meet the zero carbon target by that time will be allowed to pay a fee. A fine, if you like, which, it is touted, will be used for carbon offsetting elsewhere. Therefore, one word of warning before we go on, what you read here may well not be what will actually be required in 2016.

Who it affects

Housing Association funded projects 2008-2012 Code level 32013-2015 Code level 4 Likely to require code level 6

Everyone else via Building RegulationsAssessment mandatory for all dwellings25% carbon improvement44% carbon improvement (below 2006 Building Regulations baseline)Proposed zero carbon homes

Another, more subtle and perhaps overlooked aspect of zero carbon is that, If aiming for level 6, builders (site owners) are having to enter the power generation business at a hopelessly uneconomic scale, which somewhat ignores the efficiencies of the renewables obligation certificate system (ROCs). At present it seems that on-site renewables will be eligible for tradable ROCs, which effectively renders them part of the national renewable generation grid and despite being on-site, adding nothing, or very little, to the national total. Feed In tariffs (that have proven so successful in other European countries) to encourage more on-site generation, may well have been a better route towards 'zero carbon' than ROC's, certainly at this small scale where plant costs are high and returns are low.

Zero carbon is not the only problem facing anyone wanting to achieve Code level 6. When you get to that level other difficult requirements also kick in, some of which are step-changes, such as increasingly stringent water use restrictions. The SAP (standard assessment procedure) software that forms the basis of the Part L of the current Building Regulations also underpins the energy category of the CSH.

Background to the CSH

The CSH was developed, at least in part, in response to the European Parliament's Directive 2002/91/EC on the energy performance of buildings, itself a response to Kyoto. In 2006 the government announced the 10-year timetable towards a target that all new homes from 2016 must be built to 'zero carbon standards'. This would be achieved through a step by step tightening of the Building Regulations. Since April 2007 the developer of any new home in England could choose to be assessed against the Code.

On the 16 November 2007 the government confirmed that it would be proceeding with the implementation of mandatory ratings against the Code for all new publicly funded homes, following responses to the consultation on making a rating mandatory. From May 2008 all homes built in England need to be rated to the CSH.

 The ‘zero carbon’ home (as defined in the code)

A zero carbon' home is where net carbon emissions resulting from all energy used in the dwelling is zero. This includes the energy consumed in the operation of the space heating/cooling and hot-water systems, ventilation, all internal lighting, cooking and all electrical appliances. The calculation can take account of contributions from renewable/low carbon installations on/in the dwelling, or provided by an energy services company (ESCO) on/offsite, provided it directly supplies the dwelling. Alternatively it is acceptable to include, in the estimate of carbon emissions, the contribution from 'accredited external renewables, For a true zero carbon home, it will also be necessary to ensure that the fabric of the building significantly exceeds the standards currently required by Part L of the Building Regulations. 2000 (as amended). The 'heat loss parameter' (covering the walls, windows and other elements of the building design) must be no more than 0.8W/m2K.

CSH uses the SAP (standard assessment procedure) computation which takes into account energy consumed through heating, lighting and hot water provision. Homes will have to reach zero carbon for these factors using the SAP computation. Heat and power for this element must be generated either in the home, or on the development, or through other local community arrangements, (including district heat and power) and must be renewable (i.e. non-fossil fuel) energy. A zero carbon home is also required to have zero carbon emissions from use of appliances in the homes (on average over a year). SAP does not contain any provision for energy consumption of appliances but will be updated to do so in due course. Until SAP is updated the 'appliances' element of the qualification will be that each home must provide an amount of renewable electricity equal to a specified amount of kWh per metre squared of floor space. This additional power must be renewable power, produced either within the area of the building and its grounds, elsewhere in the development or beyond, as long as the developer has entered into arrange­ments to ensure that the renewable generation is additional to existing plans. The amount of such additional power can be reduced by any surplus from the arrangements to meet zero carbon on heating, hot water and lighting.