Part L (off plan)

Part L (Off Plan) Compliance

‘Part L’ is a form of legislation concerned with increasing the efficiency of buildings in the future. It involves testing the compliances for all newly built commercial buildings, in order to ensure less carbon is used in the future. There are various requirements for all newly built buildings under this legislation, such as:

  • The building should be designed and constructed not only to save fuels and power in order to reduce CO2 emissions relative to the buildings operation, but also to minimise heat loss and gain through the building fabric and services distribution.
  • The building should be designed and constructed to avoid excessive solar gain, in order to reduce the requirements for artificial cooling.
  • Approved calculation methodologies, testing and commissioning are to be used to demonstrate that a building meets the requirements. In addition to this, appropriate operation and maintenance manuals are required in order to dispose of any un-reasonable carbon emissions that occur during use.

 For all new commercial buildings, you are required to submit SBEM & Solar gain calculations to demonstrate your building complies with Part L2a of the building regulations. The report provides a Target Emission Rate (TER) and Building Emission Rate (BER) for the proposed building.

Upon completion of the works, a pressure test to show that the air permeability is within reasonable limits may be required before final adjustment calculation can be submitted to reflect any changes during construction and confirm consistency with the BER.


For building extensions of over 100sqm and more than 25% of the floor area of the existing building SBEM calculation will be required by building control.

Additionally, if the existing building has more than 1000sqm of floor area, additional improvements to the existing building will be required to demonstrate compliance to Part L2b.

What are the benefits of Part L2a?

Although the Part L legislation will affect aspects of the building’s design, it doesn’t restrict all design ideas as there are no prescriptive requirements, the standards are kept to a minimum. This policy can provide various benefits to insulation levels, glazing, and the shading of a building. The other factors that can be improved are the boiler efficiency, lighting efficiency and control, fan and pump efficiencies, air and water pressure drops and also heat recovery.

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