Building Regulations Explained

Building Regulations are the technical rulebook for safe, sound building work, and they matter on almost every renovation, even when planning permission does not. Here is what they cover, when they apply, and why the completion certificate is so important.

What are Building Regulations?

Building Regulations set the minimum standards for the design and construction of building work, covering structure, fire safety, insulation, ventilation, drainage and electrical safety. They are entirely separate from planning permission: planning decides whether and how something looks, Building Regulations decide how it is built.

The regulations themselves are short. The detail sits in a series of Approved Documents, each lettered, which show accepted ways of meeting them. You can meet a requirement another way if you can demonstrate it works, but on a domestic project you will almost always follow the Approved Document.

Building control is itself now regulated. Since October 2023 the Building Safety Regulator oversees the sector, private inspectors are called registered building control approvers rather than approved inspectors, and the individual inspectors on your job must be registered too.

Which Approved Documents matter for domestic work?

Four carry most of the weight on a typical London renovation: A, B, L and P.

Others appear regularly without being the headline: Part C for damp, Part F for ventilation, Part H for drainage, Part K for stairs and guarding, Part M for access, and Part S for electric vehicle charge points.

Part L is the one currently moving. The 2021 edition, incorporating the 2023 amendments, is the version in force. The Future Homes Standard edition was published on 24 March 2026 and applies to work from 24 March 2027, with transitional arrangements to 24 March 2028. It is aimed principally at new homes, but the same volume carries the standards for work to existing dwellings, so a scheme designed late in 2026 for a 2027 start should be checked against it.

When do they apply?

Most building work is covered. Common notifiable works include:

• Structural changes such as removing a load-bearing wall
• Extensions and loft conversions
• Electrical rewiring and new circuits (Part P)
• New or relocated bathrooms and kitchens involving services
• New heating systems and boilers
• Replacement windows, drainage and insulation upgrades
• Underpinning, and cutting new openings in external or party walls

Purely cosmetic work, such as decorating or a like-for-like kitchen in the same layout, usually does not. Nor does replacing a socket faceplate, a like-for-like radiator, or a fence.

A job can need Building Regulations approval and no planning permission at all, which is where most people come unstuck. Knocking two reception rooms together under permitted development is the classic case: no planning application, but a steel beam, a Part A calculation and a Building Control inspection. If a party wall is involved you must also serve notice under the Party Wall Act, a third separate process.

Building notice or full plans: which should you use?

Use a building notice for small, simple work you are confident complies, and a full plans application for anything structural. Both cost the same in total; what differs is whether anyone checks the design before you build it.

Our recommendation is simple: if steel is going in, use full plans. Having the calculations checked before the beam is fabricated is worth more than the fortnight it costs you, because a rejected padstone detail after the steel is on site is expensive.

How sign-off works

The work is inspected at set stages by either your local authority Building Control or a private registered building control approver, and every stage has to be seen before it is covered up. A typical extension runs like this:

1. Commencement. Notify Building Control before work starts.
2. Excavation and foundations. Trenches checked for depth and ground conditions before concrete goes in, then the concrete once poured.
3. Damp proof course and oversite. Checked before the floor slab is laid.
4. Drainage. Inspected while open, then again on backfill and test.
5. Structural elements. Steelwork, padstones, bearings and connections, before anything is encased or plastered.
6. Roof and insulation. Checked before boarding out.
7. Completion. Final inspection, certificates collected, completion certificate issued.

Give 24 to 48 hours' notice for each visit. The stage that costs real money when missed is the structural inspection: if a beam is plastered over unseen, you may be opening the ceiling back up to prove it.

What do Building Control fees cost in London?

For a domestic extension or loft conversion, expect roughly £980 to £1,410 including VAT, and around £400 to £720 for smaller items such as a structural opening or a chimney breast removal. Charges are set borough by borough.

Two things are easy to miss. Boroughs discount combined work, so a loft conversion and a rear extension booked together usually cost less than the two charges added up. And where work is done by someone on a competent person scheme, such as a Part P registered electrician or a Gas Safe engineer, they self-certify and there is no Building Control charge for that element.

Why does the completion certificate matter when you sell?

Because your buyer's solicitor will ask for it, and its absence turns into a price reduction, an indemnity policy or a delay at exchange.

Keep it with your deeds, along with the trade certificates covering their own elements: the Part P compliance certificate and Electrical Installation Certificate, the Gas Safe notification, and the FENSA or Certass certificate for replacement windows. A completion certificate only covers work that was actually notified, so self-certified electrics need their paperwork kept separately.

What if work was already done without approval?

You apply for a regularisation certificate, a retrospective application covering unauthorised work carried out on or after 11 November 1985. The council will normally want parts of the work opened up for inspection, and the charge is the equivalent standard charge plus a 50% uplift.

It is not automatic. If the work does not comply you have to bring it up to standard first, which can mean rebuilding elements. The enforcement window is long: under the Building Act 1984, as amended by the Building Safety Act 2022, a local authority can require non-compliant work to be altered or removed, and can prosecute, for up to ten years after completion.

It is always cheaper to do it correctly the first time. GS Renovation manages Building Control on every project that needs it, so you receive the right certificates. For advice, contact us or call 07472 424 226.