What is the Code for Sustainable Homes?
The Code for Sustainable Homes was introduced in England in April 2007. The Code is intended to improve the overall sustainability of new homes by setting a single framework within which the home building industry can design and construct homes to higher environmental standards.
From May 2008 those selling new homes will be required to provide information to any prospective purchaser on the sustainability of the home. Where a home is designed and built to the Code and assessed against it, a Code certificate will be provided. Otherwise, a statement of non assessment (a nil-rated certificate) will be provided.
Assessment procedures are based on BRE’ s EcoHomes System which depends on a network of specifically trained and accredited independent assessors, such as Code Star Homes.
How is it measured?
The Code measures the sustainability of a home against nine design categories, rating the ‘whole home’ as a complete package. The design categories are:
- Energy and CO2 Emissions
- Water
- Materials
- Surface Water Run-off
- Waste
- Pollution
- Heath and well-being
- Management
- Ecology
Each category includes a number of environmental issues which have a potential impact on the environment. The issues can be assessed against a performance target and awarded one or more credits.
The Sustainability Rating System
The Code uses a sustainability rating system – indicated by ‘stars’, to communicate the overall sustainability performance of a home. A home can achieve a sustainability rating from one (*) to six (******) stars depending on the extent to which it has achieved Code standards. Energy efficiency and water efficiency categories also have minimum standards that must be achieved at every level of the Code, recognising their importance to the sustainability of any home.
Achieving a Sustainability Rating
The sustainability rating which a home achieves represents its overall performance across the nine Code design
categories. Minimum standards exist for a number of categories – these must be achieved to gain a one star (*) sustainability rating.
Energy efficiency and water efficiency categories also have minimum standards that must be achieved at every level of the Code, recognising their importance to the sustainability of any home.
Minimum Standards
Mandatory minimum performance standards are set for some issues. For four of these, a single mandatory requirement is set which must be met, whatever Code level is sought. Credits are not awarded for these issues. Confirmation that the performance requirements are met for all four is a minimum entry requirement for achieving a level 1 rating. The four un-credited issues are within:
- Environmental impacts of materials
- Management of surface water run-off from developments
- Storage of non recyclable waste and recyclable household waste
- Construction site waste management
If the mandatory minimum performance standard is met for the four un-credited issues, two further mandatory issues need to be considered. The two issues with increasing mandatory minimum standards are:
- Dwelling emission rate
- Indoor water use
Weightings, Credits and Percentage Points
This table shows how weightings are applied across all Code categories of environmental impact to adjust the relative values of credits within different categories. Within each category credits are awarded for achieving specified degrees of performance. The weighting factors show the contribution made by each category to the total performance recognised and rewarded by the Code. The total available contribution is expressed as 100 per cent. The weighting of each category is expressed as a fraction of this, such that the sum of all the category contributions equals 100 per cent.
As an example, the 29 credits available for Energy and CO2 emissions contribute to 36.4 per cent of the total available performance. Similarly, the 4 credits available for pollution contribute to 2.8 per cent of the total available performance. By dividing the weighting factor by the number of credits for each category, we arrive at an approximate weighted value for each credit.
It is important to note that weightings apply at the category level and not for individual credits to avoid rounding errors.
The assessment process should proceed in a logical order through the environmental impact categories and issues.
- It should begin with a check that the four mandatory issues for which no credits are awarded have been achieved
- The mandatory credits for CO2 emissions and for internal water use should be checked and confirmed at the minimum values required to meet the Code level sought
- The remaining tradable credits should be checked and confirmed so that they too contribute to the required Code level.
If any of the standards for the four non-creditable issues are not met, then a zero rating will result, regardless of the other credits achieved, including the creditable mandatory issues.
Total Percentage Points Score and Resulting Code Level
For every category, the number of credits achieved is divided by the total available and multiplied by the category weighting factor to give a percentage point score for the category. This number should be rounded down to two decimal places before the next step.
The rounded percentage point scores for each category are then summed to arrive at the
Total percentage points score for the dwelling. The Total percentage point score must be rounded down to the nearest whole number.
The Code Level is then derived from the Total percentage points according to Table 6. Each
Code Level is represented on the certificate by an equivalent number of Stars from 1 to 6.
Example of Nil Rated Certificate
Example of Final Certificate
Further example of Final Certificate
