United Kingdom

New buildings
Approved Documents L1A & L2A

These set out five criteria which must be met if a new building is to meet the requirements of Part L. The criteria apply to dwellings and to buildings other than dwellings, although the methods of demonstrating compliance vary between building types.

1. Achieving the Target carbon dioxide emission rate

Carbon dioxide emissions from the proposed building must be lower than a target rate. The process for calculating the target and design rates is:

• calculate the carbon dioxide emissions per square metre of floor area from a notional building of the same dimensions as the proposed building, which would have passed the 2002 regulations by the Elemental method – see table 06.

Table 06 Elemental U-values for 2002 notional buildings(W/m²K)

• apply an improvement factor and a low or zero carbon (LZC) benchmark (see table 05) to the calculated rate: the resultant figure is the Target carbon dioxide emission rate, the TER.

For dwellings:

TER = (C_Hx fuel factor + C_L) x (I - improvement factor)
C_H= carbon dioxide emissions from heating and hot water
C_L= carbon dioxide emissions from lighting

For non-dwellings:

TER = C_notional x (I - improvement factor) x (I - LZC benchmark)
C_notional = carbon dioxide emissions from a notional buiding

Table 05 Improvement factors and low or zero carbon (LZC) benchmarks

^††The LZC is intended to implement Article 5 of the EPBD by ensuring the use of low or zero carbon energy supply system is considered before construction starts.

• calculate the carbon dioxide emission rate for the proposed building: the Dwelling emission rate (DER) for dwellings, or the Building emission rate (BER) for other buildings.

• the building meets the criterion if the DER or BER is equal to or lower than the TER. For dwellings (up to 450m² floor area) the calculations use the SAP 2005 methodology implemented in an approved SAP program. For other buildings the calculations are performed by the SBEM, using software from the ODPM augmented if necessary by other approved software. Both methods take account of heat loss through air infiltration and thermal bridging.

2. Limits on design flexibility

The emissions rating assessment allows designers considerable flexibility in the methods they employ to achieve the required rating. To ensure the building’s fabric and services are reasonably energy efficient they must perform no worse than the limits set out in the Approved Documents - see table 07. An air permeability limit of 10m³/m²/hr @ 50Pa applies to all buildings.

Table 07 Limiting U-values – New build (W/m²K)

^a dwellings ^b non - dwellings

3. Limiting the effects of solar gains in summer

Lowering elemental U-values and improving airtightness bring a risk of building interiors overheating in summer as a result of solar gain. Both SAP and SBEM assessments will test for overheating and indicate if there is an excessive risk.

4. Quality of construction and commissioning

The standard of construction must ensure the actual performance of the building is consistent with the predicted carbon dioxide emission rate. To achieve that:

• The thermal insulation must be reasonably continuous around the building envelope. Designers should use approved construction details or be able to demonstrate equivalent levels of performance in proposed alternative details.
• measured air permeabilities must be lower than the values used in the emissions calculation and less than 10m³/m²/hr @ 50Pa. Whilst all buildings other than dwellings must be tested, only a sample of dwellings within a development need be tested (the size of the sample depends upon the adoption of approved construction details and the results of the first test.)
• building services must be properly commissioned: in some cases that may involve air leakage testing of ductwork.

5. Operating and maintenance instructions

The owner of the building must be provided with sufficient information to enable the fixed building services to be efficiently operated and maintained.