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London — Tier-1 Pillar

London Part L Compliance — 2021 Uplift, Future Homes Standard 2025

London Part L 2021 compliance reality. Approved Document L 2021 notifiable thresholds, EPC uplift requirement, Future Homes Standard 2025 gas-boiler phase-out, SAP calculations, air-tightness testing, U-value targets. £2K-£20K typical compliance layer.

~2 min read·Updated 2026-04-23

Approved Document L of the Building Regulations — Conservation of Fuel and Power — sets the energy-efficiency standard for every notifiable work item in England. The 2021 uplift sharply raised fabric and heating-system requirements. The Future Homes Standard, effective 2025, raises the bar further and effectively ends new gas-boiler installations in new dwellings.

In London renovation terms, Part L compliance is a working constraint on every extension, loft conversion, window replacement, heating-system upgrade, and rewire. Elements of work must meet the target U-value (walls 0.18 W/m²K, roofs 0.15 W/m²K, floors 0.18 W/m²K, windows 1.4 W/m²K for new openings or 1.6 W/m²K for replacements). New extensions must demonstrate overall compliance via SAP calculations. Air-tightness testing is required on most new-dwelling work to meet the 8 m³/h.m² target. EPC rating must be issued on completion.

AskBaily routes London Part L compliance to a builder with a designated SAP assessor partner, air-tightness testing capability, and a track record of Part L sign-off without last-minute U-value surprises.

Part L 2021 compliance checklist

  • U-values. Walls 0.18, roofs 0.15, floors 0.18 (new-build) / 0.25 (refurb), windows 1.4-1.6.
  • SAP calculation. For new extensions and new dwellings. Pre-construction and as-built.
  • Air-tightness. 8 m³/h.m² target. Pre-completion test for new dwellings.
  • EPC. Issued on completion. Band uplift documented.
  • Future Homes 2025. No new gas boilers in new dwellings. Heat pumps or heat networks.

Frequently asked questions

Does Part L apply to a small extension? Yes. Every notifiable work item triggers Part L. A small rear extension needs to meet the new-build U-values on the new walls, roof, floor, and windows.

What is a SAP calculation? Standard Assessment Procedure — the government's methodology for calculating a dwelling's energy performance. Required for new extensions above a threshold and all new dwellings. Outputs the EPC rating.

Does the Future Homes Standard affect my renovation? Yes, from 2025, new dwellings cannot have gas-boiler heating. For extensions and renovations of existing dwellings, boiler replacement can continue under transitional arrangements — but the trajectory is clearly toward heat pumps.

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