13 January 2023

Part L 2021 edition: non-domestic buildings summary

The Building Regulations have been amended to reflect the need for non-domestic buildings to move towards net zero carbon in operation.


Since June 15th, 2022, the latest changes to Part L will set our feet firmly on the road to net zero carbon in operation again, with England requiring a 27% reduction in emissions over the 2013 standard.


With the changes taking effect from 29 March 2023 in Wales this follows a very similar approach to England, and with an average 28% reduction in emissions with some slight differences in terms of fabric performance.

Part L 2021 – When does it come into force?

The Amendment Regulations and accompanying Approved Documents L: Volumes 1 and 2 came into force on 15 June 2022.

The changes will not apply in relation to building work where a building notice or an initial notice has been given to, or full plans deposited with, a local authority before 15 June 2022 provided that the building work has started before 15 June 2023.

Part L Tata Steel construction thermal scan

What has changed?

There are some significant differences in how compliance can be achieved this time round

The first thing of note is the introduction of ‘Primary Energy’ as an additional metric by which performance is measured. Carbon emissions has been retained as a main metric, allowing some consistency in the benchmarking process – both metrics must be met for a building to comply.

The understanding of primary energy is that it is a naturally occurring form of energy that has not undergone any kind of conversion or process, for example raw fuel such as crude oil or natural gas.

The primary energy demand for a building factors in the fabric performance of the building and the efficiency of the heating technology used.

Alongside the two primary metrics, the minimum thermal performance requirements of the building envelope have been retained and tightened.

Previously the building fabric limiting values were not particularly demanding, and in most cases, buildings needed to meet the much more rigorous values set out in the notional building models to achieve compliance.

The new minimum insulation requirements (U-value) now more closely reflect those of the notional building.

The maximum allowable backstop level of air permeability has also been tightened..

Part L2: 2021 – Notional Building Specification. Building envelope

Element 2002 Notional