What building regulations apply to an extension?

Short answer

Almost every extension, loft or garage conversion needs building regulations approval, even when planning permission is not required. The regulations cover structure, fire safety, insulation, ventilation, drainage, electrics and glazing, and the work is inspected at key stages before a completion certificate is issued.

Planning permission versus building regulations

Planning permission is about whether a building is acceptable in its location: size, appearance and effect on neighbours. Building regulations are about how it is built, so that it is safe, healthy and energy efficient. You can need one, both or (rarely) neither.

The main requirements

Structure: foundations, beams and lintels designed for the loads, usually with an engineer’s calculations.
Fire safety: escape routes, smoke alarms and fire doors, especially for loft conversions.
Energy: insulation and glazing to current standards; large areas of glazing may need calculations.
Ventilation: extract fans in kitchens and bathrooms and background ventilation.
Drainage: new connections, and permission from the water company to build near public sewers.
Electrics: notifiable electrical work must be certified.
Glazing safety: safety glass in doors and low-level windows.

Who approves the work?

In England and Wales you can use the council’s building control service or a registered building control approver. In Scotland a building warrant from the council must be granted before work starts. In Northern Ireland approval comes from the council. We make the application and book the inspections.

Inspections and completion

Typical inspections are at foundation excavation, damp-proof course, drainage, insulation and completion. Keep the completion certificate safe: you will need it when you sell.

Sources and further reading

This guide is general information, not legal or tax advice. Rules change and depend on your property; we confirm what applies to your project at the survey.