UK Building Regulations 2026: Key Changes You Need to Know

Energy efficiency (Part L) — A new extension is a new thermal element in an existing dwelling, so Table 4.2 of Approved Document L Volume 1 applies: a maximum U-value of 0.18 W/(m²K) for walls, 0.15 for roofs, 0.18 for floors and 1.4 for windows. These are the 2021 edition figures, which came into force on 15 June 2022 and remain current — they are not a 2026 change. Note the limits differ for a whole new dwelling, where Table 4.1 allows 0.26 for walls.

The 2026 edition is published but not yet in force — Approved Document L: Energy and greenhouse gas emissions, Volume 1: Dwellings (2026 edition) takes effect on 24 March 2027 for building work not connected with higher-risk building work, and on 24 September 2027 where it is. Transitional arrangements are set out in Circular Letter 01/2026. So work starting today is still assessed against the 2021 edition, and a contractor telling you otherwise is ahead of the regulations rather than abreast of them.

Ventilation (Part F) — Approved Document F was reissued alongside Part L in the same 2021 round, with extract rates for kitchens, bathrooms and utility rooms. Same in-force date, same point: current, but not new this year.

Fire safety (Part B) — A loft conversion creating a third storey triggers escape requirements: a protected stairway, fire doors to rooms opening onto it, and mains-linked alarms. Sprinklers apply to blocks of flats above 11m, not to a domestic loft conversion — confirm the current Approved Document B with your building control body.

Electrical safety (Part P) — Part P governs fixed electrical installations in dwellings; EV charge point and solar wiring is covered by BS 7671 and the relevant competent person scheme rather than by a separate 2026 rule.

Sources: Approved Document L Volume 1, 2021 edition incorporating 2023 amendments, Tables 4.1 and 4.2; Approved Document L Volume 1, 2026 edition, effect dates as printed on its title page. Both retrieved from gov.uk on 2026-09-04. England only — Wales, Scotland and Northern Ireland set their own building standards.

If you are planning an extension, loft conversion or other building work, these changes may affect your costs and timelines. The stricter insulation requirements in particular can add £1,000–£3,000 to a typical extension project.

Always check with your builder or architect that your plans comply with the latest regulations. Using a tradesperson registered with a competent persons scheme means they can self-certify compliance without involving building control.

Compliance is demonstrated on paper before it is demonstrated on site: building control signs off against a drawing set showing insulation build-ups, structural members, fire strategy and drainage. If your project needs that package, building regulations drawings and fixed-fee building-regs packages both cover it, and a summary of permitted development rights is worth reading first if you have not yet established which consent route applies.