UK Construction and Law

Approved Documents L and F are corrected by circular, and the revised guidance takes effect on 24 March 2027

By Staff Writer  |  9 September 2026

Circular 04/2026, signed on 8 September, approves revisions under section 6 of the Building Act 1984 to the 2026 editions of Approved Document L volumes 1 and 2 and Approved Document F volume 1. The changes correct errors in the party wall table, the shading heights, the glazing note and the renewables paragraph, add biogas and biomass to the sleeving table, and clarify how heat network sleeving is calculated. They take effect on 24 March 2027, or 24 September 2027 for higher-risk building work.

The 2026 editions were published on 24 March 2026. Monday's circular and the letter that accompanies it, both from the Ministry of Housing, Communities and Local Government and both signed by the deputy director for new build standards and performance, give formal notice of approval of the revisions and list them clause by clause. The circular applies to buildings and building work in England and gives no technical advice of its own.

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.

Keeran Jugdoyal, Deputy Director, New Build Standards and Performance, MHCLG, circular letter of 8 September 2026

Volume 1, dwellings

Table 1.2, which lists the low carbon heat sources that can be included in a declaration of sleeving capacity, gains biogas and biomass alongside biofuels, and its entry for waste heat becomes recovered heat. Paragraph 2.10b gains new wording on sleeving: calculations should take account of the performance of the heat generation system that sleeving is applied to, and the performance of distribution circuits and storage should be applied pro rata to the proportion of heat supplied under the sleeving arrangement compared with the network as a whole.

Table 2.1, the Home Energy Model condition for party walls, is corrected for one entry: an unfilled cavity with effective sealing around all exposed edges and in alignment with the insulation layers in abutting elements, for a concrete frame building containing flats, moves from no heat loss to heat loss. Anyone who has modelled a concrete framed block of flats on the published table since March should check the effect.

Paragraphs 3.4b and 3.4c, on limiting heat gains, change the shading device height from 1.48 metres plus or minus 25 per cent to 1.48 metres minus 25 per cent. Note 4 of Table 3.1, the limiting U-values for new fabric elements, now reads window unit with standard thickness (6mm). Paragraph 5.68 loses the sentence that required the output of other renewable electricity technologies to match the standards in paragraphs 5.73 and 5.74, because the section applies to all on-site renewable generation and the indicative outputs for L3 are at paragraph 5.70.

Volume 2 and Approved Document F

Volume 2, buildings other than dwellings, carries the same corrections in its own numbering: Table 1.2 for biogas, biomass and recovered heat, paragraph 2.7b for the sleeving wording, paragraphs 3.2b and 3.2c for the shading height, and Note 8 of Table 3.1 for the 6mm glazing note. Appendix G updates two references, TM39 Building Metering and Monitoring from 2009 to 2026 and BG 49 Commissioning Air Systems from 2015 to 2024.

Approved Document F volume 1 changes in one place. Paragraph 1.79 loses the words that confined the use of a short length of flexible ductwork for the final connection to fan units to centralised continuous mechanical extract and heat recovery systems, so the allowance now applies to all system types.

Dates and transition

The revised documents take effect on 24 March 2027, except for work to a higher-risk building or to an existing one, where the approval takes effect on 24 September 2027, in each case subject to the transitional provisions described in Circular 01/2026. The revised versions are on gov.uk now and hard copies are expected from the publisher shortly. Annex A of the circular sets out the regulations each document is approved against, including regulations 6, 11F, 22 to 28, 40 to 44ZA and Schedule 1 Part L for volume 1, and regulations 39, 40C, 42, 44 and Schedule 1 Part F for the ventilation document.

Nothing in the circular changes the underlying standard. What it changes is the text a designer, an energy assessor or a building control body will be measured against from March 2027, and a table that has been wrong since 24 March 2026 on the one party wall condition most likely to appear in a block of flats.