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This circular clarifies how new buildings must meet Regulation 25B of the Building regulations 2010 (as amended).

Building regulations circular

Circular number: WGC 002/2021 Date issued: 25/02/2021
Status: For information

Nearly zero energy buildings requirements for new buildings

Issued by: Francois Samuel: Head of Building Regulations
Addressed to: Please forward to:
Local Authority Chief Executives

Welsh Local Government Association

Association of Corporate Approved Inspectors

Construction Industry Council

Competent Persons Forum
Local Authority Building Control Officers

 Members of the Senedd
This is a circular letter that clarifies the implementation of the requirements for new buildings to meet Regulation 25B of the Building regulations 2010 (as amended), which sets out that all new buildings should be nearly zero energy buildings from 31 December 2020.
For further information contact:
Paul Keepins

Building Regulations

Welsh Government Offices

Merthyr Tydfil

CF48 1UZ
Direct Line: 0300 062 8646


The purpose of this letter is to clarify the implementation of the requirements for nearly zero energy buildings for new buildings, with respect to Regulation 25B of the Building Regulations 2010 (with the exception of new buildings owned and occupied by public authorities, which were required to be nearly zero energy buildings from 1 January 2019 – the implementation of the requirements for these buildings was set out in a previous circular letter). 

This letter sets out guidance for new buildings, which are required to meet Regulation 25B from 31 December 2020.


The guidance in this Circular Letter applies to buildings and building work in Wales and excludes buildings owned and occupied by public authorities.

Regulation 25B

Regulation 25B states: ‘Where a building is erected, it must be a nearly zero-energy building’.

For new buildings occupied and owned by public authorities, the coming-into-force date for Regulation 25B is 1 January 2019.

For all other new buildings, the coming-into-force date for Regulation 25B is 31 December 2020.

Compliance with Regulation 25B

The minimum level of compliance with this requirement may be achieved by meeting the Target Emission Rate required under Regulation 26, and in addition for non-domestic buildings, the Primary energy consumption rate under regulation 26A.

Those carrying out the work should also undertake an analysis of the technical, environmental and economic feasibility of using high efficiency alternative systems, which include decentralised energy supply systems based on energy from renewable sources and taking this analysis into account as required by Regulation 25A.

Please note that the energy efficiency standards of the building regulations are currently under review.  We have consulted on a significant interim improvement to the energy efficiency standards for new homes as a first step towards the Part L 2025 standard. More information can be found at: 

Building regulations Part L review

Building Regulations Part L and F Review – Stage 2A


Any enquiries on this Circular Letter should be addressed to:

Francois Samuel, Building Regulations, Welsh Government, Rhydycar, Merthyr Tydfil, CF48 1UZ.

Telephone: 03000 628232.

E mail   

Yours faithfully,

Francois Samuel

Head of Building Regulations