Part L Building Regs

Part L Building Regulations

Changes to Part L Building Regulations are now in force

15 June 2023

The long-awaited changes to the UK Building Regulations were finally published in December 2021 and have now come into force (15th June 2023). They will not apply to work subject to a building or initial notice or completed planning application submitted before then - provided the work started on-site before the 15th of June 2023.

What has changed?

The 2021 edition of Approved Document L, Volume 1, introduces new minimum efficiency standards (backstop values) for new and replacement thermal elements, windows, and doors. The new SAP 10 (Standard Assessment Procedure) method will assess new build schemes.

Most new window types, including roof windows and glazed doors, must now achieve an improved U-value of 1.6 W/m2K compared to 2.0 W/m2K. However, the U-value of the glass will have to be much lower than this to enable a new dwelling to achieve its target for primary energy, carbon emissions and fabric energy efficiency rates.

An introduction of the following standards for replacement windows, doors and roof lights in existing dwellings are listed below.

Fabric Element Maximum U-Value (W/M2K)
Window (including roof window or curtain walling) 1.4 or minimum WER Band B
Rooflight 2.2
Doors with greater than 60% on internal face glazed 1.4 or minimum Door Set Energy Rating (DSER) Band C
Other doors 1.4 or minimum Door Set Energy Rating (DSER) Band B

Changes include;

  • For timber windows, a maximum U-value of 1.6 W/m2K or WER band C was permissible until 14th June 2023. NOW From 15th June 2023, the whole standard of a maximum U-value of 1.4 W/m2K or WER band B applies.
  • For timber doors, a maximum U-value of 1.8 W/m2K or DSER band E was permissible until 14th June 2023. NOW Fromm 15th June 2023, the entire standard of a maximum U-value of 1.4 W/m2K or WER band C / B applies.
  • For external fire door sets, a maximum U-value of 1.8 W/m2K is permissible.

As for new dwellings, the U-value for glazing has been tightened to a notional target of 1.2 [W/m2K], compared to 1.4 in the previous edition. Many glass manufacturers will now provide products that have a Ug value of 1.0 to meet the new regulations. This is because the complete window system, including its frame, spacer bar, must be considered when calculating the U-value. To achieve a notional UW-value of 1.2, house builders and architects need to most likely specify glass products with a Ug-value of 1.0 W/m2K or better.

How Can JMS Help?

JMS is able to calculate the u value of your window design in real time for any section sizes, timber species, and glass configuration in accordance with BS EN 1007-1:2017 Part 1 - (Thermal performance of windows, doors and shutters). This will mean that you will know instantly whether your window design complies with the latest regulation without the need to test. Joinerysoft believe they have one of the most flexible u-value calculators available to Joiners. It even has the ability to run two u-value calculations at the sametime As the regulations allow window manufacturers to calculate the u-value using a model size or the actual size JMS runs both calculations at the same time to enable the joinery manufacturer to potentially present the lowest value if there is a difference.


u-Value Certificate

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