Regarded as a ‘steppingstone’ along the Government’s 2050 net zero energy pathway, the updated approved document Part L came into effect on the 15th June 2022.
Key changes included:

CO2 Emissions:

It will be 27% more difficult to demonstrate compliance in comparison with the 2013 regulations.

Primary Energy Metric Introduced:

Primary Energy as the new principal energy performance metric has been introduced. The Building Primary Energy Rate (BPER) will need to be equal to or greater than the Target Primary Energy Rate (TPER).

New Minimum Requirements for Fabric:

Statutory minimum U-values have been tightened in general. As before, the Actual building performance will be compared to the Notional building which has a fabric specification even better than the backstop U-values.
Continuous thermal bridging will now need to be calculated and entered within the compliance calculation.

On Site Electricity Generation:

If the actual building has spaces which are not heated by heat pumps, then the calculation will add a proportion of PV to the Notional building, thereby reducing energy targets.

Weather data:

The CIBSE Rest Reference Year (TRY) weather data set used for calculations has been upgraded to 2016 versions of the 14 UK locations covering England.


In the Notional building the lighting efficacy has been lifted from 60.0 lumens per circuit watt (Lm/W) to 90.0 Lm/W in the 2021 update.

Actual Energy Forecast:

For new buildings with a floor area over 1,000m2, a forecast of the actual energy use of the building should be calculated and issued at as-built stage.

Solar Photovoltaics (PV):

If the actual building has spaces which are not heated by heat pumps, then a carbon penalty will be applied in the way of adding a proportion of PV to the Notional building. This carbon penalty may be overcome in many ways (not just PV installation), not least through the introduction of heat pumps.


There have been several other enhancements and improvements to the 2021 calculation over 2013 standards in relation to the building HVAC and emission factors.


Key Takeaway Points:

  • Fabric first: Uplift in U-values and air tightness.
  • Construction Details: Calculate thermal bridging values.
  • Space heating: Assume heat pumps or accept the PV penalty.
  • PV Penalty: This is not an instruction to install PV in the actual building, the shortfall can be met flexibly with other building improvements.
  • Engage: More detailed energy modelling is required, this is better done early in the design process.


Speak to our Principle Building Physics Consultant, Paul Shipley, to find out more about how this will affect your buildings.