Extension building regulations: what is checked

1. Which approval route should you choose?

GOV.UK says a full plans decision comes within five weeks, or two months with your consent, while a building notice allows work to start two days after it is submitted but gives no formal approval.

Building regulations approval is a different check from planning permission. GOV.UK says you may need both, and that the person carrying out the work is accountable for compliance and can be prosecuted and fined if the work does not comply. Planning Portal says most extensions of a property need approval, with some exemptions, so assume you need it until a building control body tells you otherwise.

In Rugby, Rugby Borough Council says Warwick Building Control, a partnership between Rugby Borough Council and Warwick District Council, now runs the building control service. GOV.UK also lists a private registered building control approver as an alternative for most non-higher-risk work, with fees negotiated directly.

Check the guidance: GOV.UK: building regulations approval, GOV.UK: how to apply for building regulations approval, Rugby Borough Council: Warwick Building Control, Planning Portal: is building regulations approval needed for an extension, Warwick District Council: making a building regulations application.

2. What do inspectors actually look at?

There is no single national stage list, so the surveyor sets the inspection plan, and published council examples show visits timed before work is covered.

Councils publish their own inspection examples, and they differ. Ealing gives an example plan for a single storey extension and says the surveyor decides the final inspections needed. Torbay lists ten stages in order. Neither is a Rugby schedule. Use them to understand the logic, then ask the Warwick Building Control surveyor for the plan on your own project.

The logic is simple. Inspectors need to see work before something else hides it: ground before concrete, concrete before backfill, drains before they are buried, the roof structure before felt and battens, and wiring and framing before plasterboard. Commercial blogs repeat similar lists, such as Planning Signal, last reviewed 10 April 2026, but they cite no legislation, so treat them as context only.

The table below draws only on those two council pages. It helps you read your own inspection plan, and is not a promise about your address.

Check the guidance: London Borough of Ealing: building control site inspections, Torbay Council: building control site inspections, Planning Signal: building control homeowner guide.

3. What happens at foundations and groundwork?

Foundations are the first point where a builder needs the surveyor on site, because Planning Portal says the foundation cannot be poured until undisturbed ground has been found.

Planning Portal explains that foundations must carry the load of the building safely to the ground. Soil type matters, and clay soils can expand and contract with moisture changes, mainly to about 0.75m deep, so foundations should go deeper than that. Excavation should normally reach at least the depth of a neighbouring foundation, and at least the invert depth of the deepest drain, sewer or trench nearby. Trees in clay areas can dry the soil enough to require significantly deeper foundations.

A two storey addition places more load on the ground than a single storey one, and Planning Portal says that affects depth and width. None of this can be judged from a photograph, which is why the trench inspection exists.

On booking, Warwick District Council says site visits can be booked online or by phone, that requests made before 10:30am Monday to Friday can be met the same day, and that Thursday visits are limited to essential ones after 1pm. It also says concrete should only be provisionally booked until foundations are approved.

Check the guidance: Planning Portal: extension foundations, Warwick District Council: building regulations.

4. Who gives notice, and how do you keep a record?

The person carrying out the work gives the notices, so your contract should say who books each inspection and who keeps the evidence.

Notice duties come from the Building Regulations 2010. Regulation 16 provides for notice when work starts, for any stage the authority specifies, and when work is complete. Torbay's page, which we opened for an example, gives the commencement notice as within five days after work has commenced and the completion notice as no later than five days after completion, and says the builder should arrange the completion inspection. Check the equivalent wording with Warwick Building Control, because councils differ in how they set stages.

A homeowner does not need to learn every notice, but does need to know who is responsible. Ask before signing who will give each notice and where the surveyor's findings will be recorded.

Check the guidance: legislation.gov.uk: Building Regulations 2010, regulation 16, Torbay Council: building control site inspections.

5. Which certificates sit alongside the inspections?

Electrical test certificates are needed before a completion certificate can be issued, and registered installers can self-certify some work.

Planning Portal lists the foundations, flooring, walls below ground, ventilation, energy efficiency and structural opening topics for extensions, and the work sections normally needed to satisfy the regulations: doors and windows, drainage, electrics, external walls, kitchens and bathrooms, internal walls and roofs. The page gives no technical requirements, so the details come from your designer and the surveyor.

On electrics, Warwick District Council says you will need to supply British Standard test certificates for most new electrical installations, so choose a contractor who can provide them. Its loft guidance adds that these certificates are required before a completion certificate can be issued. Ask the electrician, before first fix, who will supply the certificate and when.

GOV.UK says installers registered with a competent person scheme can self-certify that their work meets standards, give you a certificate within 8 weeks of completion, and inform the local council on your behalf where needed. That can apply to work such as windows or boilers, so confirm with your builder which items sit under which route.

Check the guidance: Planning Portal: is building regulations approval needed for an extension, Warwick District Council: domestic extensions guidance, GOV.UK: use a competent person scheme.

6. What if something fails or work started early?

GOV.UK says you may have to correct the work or pay a fine if building regulations are not followed, and regularisation is available only from a local authority.

If a surveyor finds that work does not comply, the sensible response is to ask exactly what must change, by when and whether a re-inspection is needed. Do not agree to cover the work first. GOV.UK says the relevant building control body can require you to pay to fix faulty work, and that without approval you may lack the certificates needed when you sell your home.

Where work has already been done without consent, GOV.UK describes regularisation: retrospective approval, available only from a local authority, for work carried out after 11 November 1985. Alterations may be needed before a certificate is issued. Some blogs quote break-out costs for opening up work, but we found no opened primary source for a figure, so we do not give one.

Agree the process early. Ask whether the builder will pause at each inspection point, how remedial work is priced and recorded, and who pays if a visit must be repeated.

Check the guidance: GOV.UK: building regulations approval, GOV.UK: how to apply for building regulations approval.

7. How do completion and the paperwork work?

For full plans, GOV.UK says you usually receive a completion certificate within 8 weeks of finishing the work, provided it complies with the regulations.

Completion is the end of the inspection sequence and the start of your paperwork file. Ealing says satisfactory compliance on site enables it to issue a completion certificate promptly, and Torbay says it cannot issue one until all relevant parties have signed the completion notice. Warwick District Council says a building notice does not produce an approval notice, which is why the completion certificate matters.

Keep four things together: the approval notice if you used full plans, the inspection log, the electrical and any competent person certificates, and the completion certificate. GOV.UK notes that certificates of compliance matter when you sell. Do not rely on a verbal assurance.

Keep the other checks separate. Planning permission, permitted development and party wall notices are different processes. Our guides on planning permission for an extension in Rugby Borough and party wall agreements in Rugby cover them. A building control completion certificate does not settle either question.

Check the guidance: GOV.UK: how to apply for building regulations approval, London Borough of Ealing: building control site inspections, Warwick District Council: making a building regulations application.

8. What should you send a builder to start well?

A clear brief lets a builder explain which approval route they expect and who handles each notice, before you compare quotations.

Send your Rugby postcode, photographs of the rear or side of the house, what the new room is for and any drawings. Say whether you have already chosen an approval route, a designer or an engineer. Say whether any drawings are for planning only.

Ask each builder four questions: which route do they expect, who gives the notices, how will inspections be recorded, and what happens if a visit finds a problem. Compare the answers alongside the price, not after it. Our guide on what a builder's quote should include shows how to check that approval fees and certificates are in scope or clearly excluded.

No part of this guide is a Belmax price or programme.

Check the guidance: Planning Portal: is building regulations approval needed for an extension.