The Low-Carbon House:
Energy Standards: Introduction

• The Energy Standards published here are a product of the AECB Carbon Lite programme funded by the Carbon Trust.

• The Standards correspond to Mandatory Levels 4, 5 & 6 set out in the Code for Sustainable Homes

• The Standards are expressed in terms of a combination of limits on space heating energy consumption, primary energy consumption and CO₂ emissions. They can also be expressed as the percentage saving in energy and CO₂ relative to the same building type in the existing building stock. See below.

There are two versions of the standards:
• performance only: expressed in energy and CO₂ emissions, albeit with some limits on U values and air leakage, allowing design freedom or catering for unusual circumstances
• prescriptive standards, which spell out the means of delivering to the targets.

The prescriptive standard is best introduction for those not used to thinking about energy in buildings. Those who have already designed many successful low-energy buildings may feel comfortable with the performance standards. We suggest that everyone first read the notes attached to the tables in both the prescriptive and performance standards.

The AECB has based the framework for supporting its standards on UK and international good and best practice. The AECB believes in developing working methods that predict the actual energy performance of buildings and the resulting CO₂ emissions to a high level of precision.

The standards do not yet take account of the energy and CO₂ embodied in the construction materials and do not determine the choice of materials. (see: 'The Code for Sustainable Homes:
Materials: A quick guide')

Code for Sustainable Homes Assessment Criteria

‘Credits are awarded based on the percentage improvement in the Dwelling Emission Rate (DER), (estimated carbon dioxide emissions in kg per m² per annum arising from energy use for heating, hot water and lighting for the actual dwelling), below the Target Emission Rate (TER), (the maximum emission rate permitted by Building Regulations), for the dwelling where DER and TER are as defined in Approved Document L1A 2006 Edition of the Building Regulations. Credits are awarded in accordance with the table below. Note that to reach Level 6 (zero carbon) there are additional requirements..’ ( 'Code for Sustainable Homes: Technical Guide', CLG 2007)

(Level 6 requirements are defined in the CSH Technical Guide).

Achieving Carbon Lite Standards will deliver CSH DER targets and the corresponding credits as follows:
• Silver Standard: Will deliver the DER target of Level 4 resulting in between 8 and 13 Credits. Additional credits will also be achieved on HLP and appliances.
• Passivehaus Standard: Will deliver the DER target of Level 5 resulting in 14 Credits.
• Gold Standard: Will deliver the DER target of Level 6 resulting in 15 Credits.

Level 4 / 'Silver'

'Silver can be summed up as best widely-available technology. It does not push the technological boundaries radically forward but it represents a big advance on normal UK building practice. The very good energy and CO₂ performance is achieved without the addition of renewables or other 'bolted-on' equipment. It is achievable using products and materials which are readily available on the UK market and can be delivered at or very close to current building costs, given care at the design stage.'

Level 5 / 'Passivhaus'

'Passivhaus maximises the use of energy efficiency technologies. It does not push the technological boundaries radically forward, but it still represents a big advance on normal UK building practice. If it were applied in full to housing, we estimate that it would lead to over an 80% reduction in CO₂ emissions, versus the average for the existing dwelling stock. If it were applied to non-domestic buildings, the reduction in CO₂ emissions, versus the average for the stock of that building type, can often be in the range 75 to 80%.'

Level 6 / 'Gold'

'Thermally the Gold Standard is almost identical to the Passivhaus Standard (www.passiv.de) or the Swiss MINERGIE P standard (www.minergie.ch). The lower primary energy use reflects savings in space and water heating, cooking, lights and appliances. The lower CO₂ emissions reflect the stronger requirements in particular for energyefficient electrical appliances/ equipment and a requirement for more electricity-producing renewables.
As a ballpark figure, the CO₂ emissions would be 5% of those of a normal UK building in the stock. This reflects the significance in buildings, which meet high thermal standards, of the CO₂ emissions due to the electricity consumed for lights and appliances.'