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  • Part L – England & Wales
    • Part L1A – New Dwellings
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For new domestic buildings, the new regulations aim to reduce carbon emissions by approximately 20% over 2002 levels.

A key change from the 2002 regulations is that compliance is now based upon whole building carbon emissions, with the former compliance methodologies (elemental, target u-value and carbon index) now scrapped.

This important change means that building designers must now take a more holistic approach to the design of their buildings, considering the impacts of both the constructional elements as well as those of the energy using services (heating, hot water, lighting and ventilation). Air tightness also now has an additional impact, with minimum standards now applying which will have to be confirmed on building completion by sample pressure testing.

Demonstrating Compliance

In order to achieve compliance, designers must show that the predicted annual carbon emissions from the building – taking into consideration the heating, hot water, lighting and ventilation systems, fuel type and performance of the building envelope – are less than or equal to a calculated target level. Designers have complete flexibility to 'trade off' the performance of each of these aspects against each other to ensure the emissions fall within the annual target.

A new version of SAP (Standard Assessment Procedure)(see: Building Regulations > SAP) has been produced to enable the necessary calculations to be carried out.

The target carbon emissions level (known as the TER) is calculated using a 'notional' building of the same floor area / shape / etc. as the one being designed, with default element u-values and heating, hot water and ventilation systems applied so a carbon emissions figure can be calculated.

A carbon emissions improvement factor and allowance factor dependent on the heating fuel type are then applied to produce the TER target, expressed in kgCO2/m2 /yr.

The predicted dwelling carbon emissions figure (known as the DER) is calculated by applying the proposed building details (floor area / shape / element u-values / air tightness / heating / hot water / ventilation system / etc.) to SAP, which will produce a predicted carbon emissions figure for the buildings.

Improvements to the building fabric elements or building services types / efficiencies improve the DER, allowing compliance to be achieved.

Block Assessment Method

For buildings containing multiple dwellings such as flats, it is permissible to use a whole block methodology to demonstrate compliance. This is done by calculating the individual TER / DER for each dwelling and calculating the floor area weighted average TER and DER for the block.

This has the distinct benefit that better performing units within the block, for example mid floor flats with less exposed surface areas, can be used to trade off against ground floor and top floor flats, meaning it is not necessary to achieve compliance for every single dwelling, only the overall block.

This also provides the ability for innovative approaches to compliance to be taken, for example installing solar water heating for the top floor flats, providing an overall carbon saving benefit for the complete block. This and other compliance options are covered in more detail in the SAP (see: Building Regulations > SAP) section of this website.