Correspondence

Amendments to Approved Documents L (Energy and greenhouse gas emissions) and F (Ventilation), Circular 04/2026 - letter

Published 8 September 2026

Applies to England

Notice of revision to Approved Document L1, L2 and F1 (2026 editions) 

Dear Sir or Madam,   

You will be aware that the department published the following Approved Documents on 24 March 2026: 

• Approved Document L (Energy and Greenhouse Gas Emissions) Volume 1: Dwellings - 2026 edition

• Approved Document L (Energy and Greenhouse Gas Emissions) Volume 2: Buildings other than Dwellings - 2026 edition

• Approved Document F (Ventilation) Volume 1: Dwellings - 2026 edition

I am writing to inform you of the revision to correct minor errors in these documents. These revisions are approved under section 6 of the Building Act 1984. The revised versions of these documents incorporating these changes are now available from the GOV.UK website. We expect these to be available from the publisher in hard copy shortly.  

Scope of this Circular Letter 

This Circular Letter relates to buildings and building work in England. 

Coming into force date 

The revised Approved Documents will take effect on 24 March 2027, except in relation to higher-risk building (HRB) work or work to an existing HRB, for which the approval takes effect on 24 September 2027, and subject in each case to the transitional provisions described in the Circular 01/2026. 

List of amendments 

Approved Document L (Energy and Greenhouse Gas Emissions) Volume 1: Dwellings - 2026 edition. 

The department has amended Table 1.2, Table 2.1, paragraphs 3.4b and 3.4c, and Note 4 of Table 3.1 to correct errors. The department has also amended paragraph 2.10b to add further clarity to the process for calculating the performance of heat networks using a sleeving arrangement. Lastly, the department has amended paragraph 5.68 as this section of the guidance applies to all installation of on-site renewable electricity generation, guidance on indicative outputs for L3 can be found at paragraph 5.70. Further details are outlined below.  

Section 1: Calculating the target primary energy rate, target emission rate and target fabric energy efficiency rate 

• Amend Table 1.2 Low carbon heat sources which can be included in a declaration of sleeving capacity to add ‘biogas’ and ‘biomass’ as entries in the table alongside ‘biofuels.’  

• Amend Table 1.2 Low carbon heat sources which can be included in a declaration of sleeving capacity to replace the table entry for ‘waste heat’ with ‘recovered heat.’ 

Section 2: Calculating the dwelling primary energy rate, dwelling emission rate and dwelling fabric energy efficiency rate 

• Amend paragraph 2.10b to add the following wording: 

‘In cases where sleeving is being used calculations should take account of the performance of the heat generation system that sleeving is being applied to. The performance of distribution circuits and storage should be applied on a pro-rated basis based on the proportion of heat being supplied under the sleeving arrangements compared to the heat network as a whole.’ 

• Amend Table 2.1 HEM condition for party walls to change the HEM condition for the ‘Unfilled cavity with effective sealing around all exposed edges and in alignment with insulation layers in abutting elements for a concrete frame construction in a building containing flats’ entry from ‘No heat loss’ to ‘Heat loss.’ 

Section 3: Limiting heat gains and losses 

• Amend paragraph 3.4b and 3.4c to replace ‘1.48m (±25%) high’ with ‘1.48m (-25%) high’. 

• Amend Note 4 of Table 3.1 ‘Limiting U-values for new fabric elements and air permeability in new dwellings’ to include ‘(6mm)’ after the text ‘window unit with standard thickness.’ 

Section 5: Carbon and energy performance of building services – system specific guidance 

• Remove the following wording from paragraph 5.68: 

‘Where another renewable technology is used to generate electricity, the amount produced by all technologies should be equivalent to the output of the standards in paragraphs 5.73 and 5.74.’ 

Approved Document L (Energy and Greenhouse Gas Emissions) Volume 2: Buildings other than Dwellings - 2026 edition. 

The department has amended Table 1.2, Table 2.1, paragraphs 3.2b and 3.2c, and Note 8 of Table 3.1 to correct errors. The department has also amended paragraph 2.7b to add further clarity to the process for calculating the performance of heat networks using a sleeving arrangement. Lastly, the department has updated references to documents in Appendix G to the correct versions. Further details are outlined below.  

Section 1: Calculating the target primary energy rate, target emission rate and target fabric energy efficiency rate 

• Amend Table 1.2 Low carbon heat sources which can be included in a declaration of sleeving capacity to add ‘biogas’ and ‘biomass’ as entries in the table alongside ‘biofuels.’  

• Amend Table 1.2 Low carbon heat sources which can be included in a declaration of sleeving capacity to replace the table entry for ‘waste heat’ with ‘recovered heat.’ 

Section 2: Calculating the building primary energy rate, building emission rate and building fabric energy efficiency rate 

• Amend paragraph 2.7b to add the following wording: 

‘In cases where sleeving is being used calculations should take account of the performance of the heat generation system that sleeving is being applied to. The performance of distribution circuits and storage should be applied on a pro-rated basis based on the proportion of heat being supplied under the sleeving arrangements compared to the heat network as a whole.’ 

Section 3: Limiting heat gains and losses 

• Amend paragraph 3.2b and 3.2c to replace ‘1.48m (±25%) high’ with ‘1.48m (-25%) high’. 

• Amend Note 8 of Table 3.1 ‘Limiting U-values for new fabric elements and air permeability in new buildings’ to include ‘(6mm)’ after the text ‘window unit with standard thickness.’ 

Appendix G: Documents referred to 

• Replace ‘TM39 Building Metering and Monitoring [2009]’ with ‘TM39 Building Metering and Monitoring [2026]’ 

• Replace ‘BG 49/2015 Commissioning Air Systems [2015]’ with ‘BG 49/2024 Commissioning Air Systems [2024]’ 

Approved Document F (Ventilation) Volume 1: Dwellings - 2026 edition 

The department has amended wording in paragraph 1.79 to clarify that a short amount of flexible ductwork can be used for the final connection to fan units in all system types. Further details are outlined below.  

• Remove the following wording from paragraph 1.79: 

‘for centralised continuous mechanical extract ventilation or mechanical ventilation with heat recovery systems.’ 

Publications 

Approved Document L (Energy and Greenhouse Gas Emissions) Volume 1: Dwellings - 2026 edition and Approved Document L (Energy and Greenhouse Gas Emissions) Volume 2: Buildings other than Dwellings - 2026 edition have been updated and are available at: https://www.gov.uk/government/publications/approved-document-l-2026 

Approved Document F (Ventilation) Volume 1: Dwellings - 2026 edition has also been updated and is available at:  

https://www.gov.uk/government/publications/approved-document-f-2026 

Enquiries 

Telephone enquiries on this Circular Letter should be addressed to the Ministry of Housing, Communities and Local Government on 0303 444 0000. All email enquiries should be addressed to ecopolicy@communities.gov.uk. 

You can alternatively submit your enquiry by post to: 

Correspondence Unit 
2 Marsham Street 
London SW1P 4DF 

Yours faithfully, 

Keeran Jugdoyal
Deputy Director
New Build Standards and Performance Division