Even if your extension is permitted development and needs no planning permission, it almost always needs building regulations approval. Planning is about whether you can build; building regulations are about whether it’s built safely and efficiently. They are two separate consents.
Two ways to get building control sign-off
- Full Plans — you submit detailed drawings for approval before work starts. Best for most extensions; you get certainty up front.
- Building Notice — a lighter route for simpler work, inspected as you go, with no approved drawings.
The key parts that apply to extensions
- Part A (Structure) — foundations, beams and loadbearing walls must be adequate.
- Part L (Conservation of fuel and power) — insulation and glazing must meet minimum U-values; this is the part most extensions are caught by.
- Part B (Fire safety) — escape routes, and protected routes where a loft is involved.
- Part K (Protection from falling) — stairs, balustrades and safety glazing near doors and floors.
- Part F (Ventilation) and Part P (Electrical safety) — adequate ventilation and safe electrical work.
Why the completion certificate matters
When work passes final inspection, building control issues a completion certificate. Keep it safe — like a Lawful Development Certificate, it’s something buyers’ solicitors ask for, and its absence can stall a sale or remortgage.
Building regs are separate from planning, so check both. See whether you need planning permission and, if you’re applying, how to avoid a planning refusal.
This guide is general information, not legal or planning advice. Planning rules change over time and are applied differently by each local planning authority (LPA). Always confirm the position with your council before starting work. Unformed’s Planning Review gives an AI-assisted risk assessment of a scheme but does not guarantee any planning outcome.