The Code for Sustainable Homes explained
The Code for Sustainable Homes might not be as complex as the Da Vinci Code, but it's certainly not straightforward. BD Online has distilled down what architects need to know. By Roderick Bunn
The Code for Sustainable Homes (CSH) aims to achieve a step-change in environmental performance of new UK homes. The Code is targeted at architects, home designers and builders of new homes. It covers water use, waste generation, and the use of low-polluting materials and processes.
Developed by the Building Research Establishment, the CSH will subsume the requirements of the current EcoHomes System. In doing so the CSH will become the single national standard for sustainable homes.
While compliance with the CSH will initially be voluntary rather than mandatory, the Code is intended to complement the forthcoming scheme for Energy Performance Certificates These are being introduced in June 2007 to meet the requirements of the Energy Performance of Buildings Directive (EPBD). The CSH is therefore likely to become mandatory in time, possibly when the Building Regulations are updated in 2008.
The minimum standards for compliance with the Code for Sustainable Homes have been set above the current requirements in the Building Regulations covering the use of energy in the home and strategies to reduce carbon dioxide emissions. This will enable it to become the platform for future improvements to the Regulations.
The definition of energy, carbon dioxide emissions and waste covers the fuel used to process and manufacture construction materials (the embodied energy element) as well as the energy used in heating, lighting, ventilation and water use.
The CSH will be applied by a system of accredited assessors trained by the BRE via its courses for EcoHomes and the BREEAM scheme, the environmental assessment method for the non-housing sector.
CSH assessors will conduct initial design assessments of a sample type of each home in a development, recommend a sustainability rating, and issue an interim CSH certificate. They will perform a post-completion check to verify the rating before a final certificate is issued. The BRE will be the training and accrediting agency.
Builders (not individual architects or designers) will receive a certificate showing the overall sustainability rating for the home, and a breakdown for how the rating has been achieved.
How the CSH works
The CSH will assess the sustainability of a home by awarding points in nine design categories. Points achieved from each category are totalled, and the total translated into a star rating for the home: Level 1 requires 33.3 points, Level 2 is set at 43 and so on up to Level 6 at 64.9 points. The nine categories are:
• Energy and carbon dioxide (including insulation, electric lighting, heating systems, domestic appliances)
• Materials (responsible sourcing of construction and finishing elements)
• Ecology (protection or enhancement of site habitats, use of the BRE’s Ecological Value Checklist)
• Waste (household recycling facilities, site waste management, composting facilities)
• Pollution (insulants with low global warming potential, low NOx emissions)
• Health and well-being (specific daylight factors for particular rooms, sound insulation, and adherence to the principles of Lifetime Homes)
• Water (internal and external potable water consumption)
• Surface water run-off (rainwater recovery, attenuation of surface water run-off, reduction of flood risk)
• Management (Home User Guide, information on the site and its surroundings, adoption of the Considerate Constructors Scheme)
As with the BREEAM scheme, the CSH awards points for achieving levels of sustainability in each of the nine categories. The totalled points are then translated into a star rating for the home. One star is the entry level for a sustainable home (above the minimum requirements of the 2006 Building Regulations) and six stars reflects “exemplar development” in sustainability terms.
Not all the categories carry the same importance. For example, minimum standards for energy and water efficiency have been set at each of the Code’s six levels. House designers must also achieve minimum standards for materials, surface water run-off and waste to achieve Level 1. But there are no minimum standards set for the pollution, health and well-being, management and ecology categories. In practice builders aiming for Level 1 will probably ignore them, and achieving points in these categories will only become a factor when aiming for Level 2 or higher.
Achieving Level 1 for energy and water (a 10% improvement over 2006 Building Regulations) must involve investment in higher thermal insulation, improved fabric air permeability, and the use of flow reducing or aerating taps throughout. But then designers can opt for a higher star rating by improving on the minimum standards for energy and water and by addressing different issues.
To rise to Level 3, a home will need to be 25% more energy efficient compared to Part L 2006. This will require investment in district heating, or low carbon technologies such as solar thermal panels or bio-fuel boilers, dual-flush toilets, and improved surface water and waste management. Extra points can be gained from investment in providing drying space (obviating the need for tumble dryers), providing a room that can be set up as a home office, and the use of more environmentally-sound materials.
Level 6 – the zero-carbon level – will require the use of solar panels, bio-fuel boilers or wind turbines in order to replace entirely the energy taken from the national grid. The additional points to achieve a six-star rating must require investment in energy efficient appliances, reduction of surface water run-off, and the application of a site waste-management plan.
Technical guidance to help house designers use the CSH will be published in April 2007. This will include a calculation and assessment tool, which will also be used to calculate the Energy Performance Certificates.
The categories - minimum standards
To achieve at least one star under the CSH, builders must achieve the mandatory minimum standards in the energy efficiency and water efficiency categories, and for materials, surface water run-off, and waste. There are no minimum standards for pollution, health and well-being, management and ecology.
1 and 2) Energy and water Efficiency
The CSH takes the minimum requirements in Part L of the 2006 Building Regulations as its baseline. All improvements on this minimum standard are expressed in percentages. For example, a single star for energy and carbon dioxide requires a percentage improvement over the Target Emission Rate (TER) in Part L of 10%, 3 stars 25%, and 5 stars a 100% improvement (see table).
The minimum standard on one star for the environmental impact of materials requires at least three of the following five elements must be specified to achieve a BRE Green Guide 2006 rating of at least D:
• Roof structure and finishes
• External walls
• Upper floor
• Internal walls
• Windows and doors
The minimum code level for waste is covered by two categories:
• Site waste management
• Household waste storage
Builders will be required to adopt a site waste management plan. This must include the monitoring of waste on site and the setting of targets to promote the efficient use of resources.
The management of household waste storage requires the containment of waste for each dwelling. The CSH requires for the greater (by volume) of:
• Either accommodation of external containers provided under the local authority’s refuse collection and recycling scheme
• Or at least 0.8 m3 per dwelling for waste management as required by BS 5906 – Code of Practice for Storage and On-site Treatment of Solid Waste from Buildings.
5) Surface water run-off
The minimum requirement of one star requires that peak run-off rates and annual volumes or run-off will be no greater than the site’s previous conditions.
Architects and designers will be judged on the provision of rainwater holding facilities (water butts) and the attenuation of run-off either to natural water courses or to municipal systems.
Where houses are sited in areas of flood risk, designers can gain extra points for constructing the ground level of buildings above the flood level, or designing the house with resilience against flooding to limit consequential damage.
Categories – without minimum standards
Architects can gain extra points by using insulants with little or no global warming potential or ozone depleting potential in either their manufacture or composition. This covers insulation materials used in walls, lofts, and roofs, as well as around hot water cylinders.
Nitrous oxide emissions (NOx) can be limited by using boilers with low NOx emissions as defined in BS EN 297: 1994.
7) Health and well-being
Health and well being covers comfort issues, such as daylight, sound insulation, the design of private external areas that are accessible by people with disabilities (although the CSH does not define those disabilities).
More points can be awarded for applying the standards of the Lifetime Homes scheme, which lays down design principles for homes designed to cater for people of all ages, and age-related disabilities.
Higher standards of sound insulation than required by Part E of the Building Regulations will also earn extra points. Architects need to be aware that this will either require post-completion testing, or proof of the application of robust details. The latter will presumably need to be signed off by the Building Control Officer, but the Code does not stipulate this.
The CSH awards points for achieving specific daylight factors in kitchens, living rooms and studies. This has not been defined precisely in the Code, which merely asks architects to refer to the Technical Guidance Manual, due to be published in April 2007.
Management covers both construction and post-construction management. Extra points can be gained by builders who abide by the Considerate Constructors Scheme, and who deliver a strategy to reduce the harmful effects of construction on the site.
Points are gained for the provision of Home User Guides, which are relevant to the operation, and environmental performance of the home.
The ecology category covers the ecological value of the site, ecological enhancement, protection of ecological features and the total building footprint. Designers and builders can win points by adopting the requirements in the BRE Ecological Value Checklist.
Points can be won by limiting the effects of house construction on the local flora and fauna, and where the designers and builders can demonstrate that anything of ecological value is protected during construction works and able to thrive after completion. Extra points can be awarded if the architect has commissioned a report from a qualified ecologist (although the Code is not explicit that the designer must act on its findings).
How the points are calculated
For the water and energy categories, the points scoring system is based on the Standard Assessment Procedure (SAP: 2005). The points are calibrated against percentage improvements over the 2006 Building Regulations, with a 10% improvement resulting in 1.2 points, and 100% resulting in 16.4 points. Achieving zero carbon results in 17.6 points.
The points scoring system differs each time for the other seven categories. This is because each category refers to existing best practice guidance.
Architects will be familiar with the guidance used to score some categories, such as the Target Emission Rate of the Building Regulations used to score the energy items, and home security guidance provided by the Association of Chief Police Officers: Secured by Design - New Homes.
The ecology category uses the BRE Ecological Value Checklist, while the waste measurement criteria is based on WRAP/Envirowise guidance. Water use and sourcing of materials are covered by bespoke CSH calculator tools. Impact to the environment will be measured using a life-cycle assessment method, with the impact graded A+ to G-.
Complications with the scoring remain as some of the guidance is not yet available. For example, the use of materials will be measured using the BRE’s New Green Guide, which has not yet been published.
Roderick Bunn is a writer and consultant on buildings