Building Regulations are often confused with planning permission — but they are completely separate. You can build an extension that needs no planning permission but still requires Building Regulations approval. Here is what you need to know.
What are Building Regulations?
Building Regulations set minimum standards for the design and construction of buildings in England and Wales. They cover structural integrity, fire safety, insulation and energy efficiency, drainage, ventilation, and electrical safety — among other things.
Unlike planning permission (which is about whether something should be built), Building Regulations are about how it is built.
Do all extensions need Building Regulations approval?
Yes, in almost all cases. The only exceptions are very minor works such as:
- A conservatory under 30m² with an opening (not a fixed) connection to the house and no heating
- A detached outbuilding under 15m² with no sleeping accommodation
- Some garden structures
For all practical purposes, any proper rear extension, loft conversion, or structural alteration will need Building Regulations approval.
How does Building Regulations approval work?
There are two routes:
Full Plans Submission
You submit detailed drawings and specifications to Building Control before work starts. They approve the plans, and then inspect at key stages during the build. This route gives you certainty before you start, but adds 2–4 weeks to the pre-build process.
Building Notice
You notify Building Control that you are starting work (typically 48 hours in advance) and they inspect during the build. No drawings are submitted upfront. This route is faster to get started, but relies on the inspector accepting your approach on site.
We manage both routes depending on the project type and timeline. For loft conversions and structural alterations, we typically use Full Plans because of the structural complexity.
What gets inspected during a rear extension?
Building Control will typically inspect at the following stages:
- Foundations: before concrete is poured
- Damp-proof course: before the slab or floor construction
- Structural elements: any steelwork, lintels, or beam installations
- First-fix electrics and plumbing: before boarding and plastering
- Insulation: wall, floor, and roof insulation before covering
- Final inspection: before practical completion
For a loft conversion, there are additional inspections for the floor structure, fire door installation, and escape window compliance.
What happens if you do not get Building Regulations approval?
Building work carried out without Building Regulations approval (where it is required) creates a significant problem when you come to sell the property. Conveyancing solicitors will ask for the completion certificate. If you cannot provide it, the buyer's solicitor will typically require you to either:
- Obtain a Regularisation Certificate (which involves opening up completed work for inspection, and can be costly)
- Take out indemnity insurance (which covers the buyer but does not mean the work meets the required standard)
We have seen properties held up in sale because of missing completion certificates from extensions built years earlier without proper Building Control sign-off. It is not worth the risk.
What is a completion certificate?
A completion certificate is issued by Building Control after the final inspection confirms that the work meets Building Regulations. It is the document that proves the extension was built correctly.
We obtain the completion certificate on every project we deliver. You receive it at the end of the project as part of your handover pack.
How much do Building Regulations fees cost?
Building Control fees for a standard rear extension in London typically range from £500 to £1,200 depending on the size and complexity of the work. For a loft conversion, fees are typically £700 to £1,500.
We include Building Regulations management in our project price — the fees are a pass-through cost.