Building Control for Extensions in England

Check the approval route

Building regulations approval and planning permission are separate processes, and GOV.UK states it plainly: “Building regulations approval is different from planning permission. You might need both.” A design that qualifies as permitted development for planning purposes has only answered the planning question; it says nothing about building regulations, which is a separate legal requirement about how the work is built rather than whether you’re allowed to build it. This guide covers England only; Wales, Scotland and Northern Ireland run separate building regulations regimes.

Most ordinary extension work does not qualify for any exemption, and floor area alone doesn’t settle the question. Schedule 2 to the Building Regulations 2010 exempts, under Class 7, ground-level additions such as “a conservatory, porch, covered yard or covered way” or “a carport open on at least two sides” only where the floor area of that extension does not exceed 30m² — and, for a conservatory or porch that is wholly or partly glazed, only if “the glazing satisfies the requirements of Part K4, K5.1, K5.2, K5.3, and K5.4” of Schedule 1. Under Class 6, a detached single-storey building with no sleeping accommodation is exempt where its floor area does not exceed 30m² and it either stands at least one metre from the boundary or is built substantially of non-combustible material; a detached building with no sleeping accommodation is exempt regardless of that condition where its floor area does not exceed 15m². A standard rear extension, a loft conversion, a garage conversion, or anything over one storey falls outside these classes and needs approval in the normal way.

A Schedule 2 exemption is not unconditional even where it applies. Regulation 9(3) applies Part P (electrical safety) to a small detached building or extension that “receives its electricity from a source shared with or located inside a dwelling” — so a garden room wired from the house consumer unit still has to meet Part P, even though the structure itself is exempt. Regulation 9(2) does the equivalent for water: the Part G water-safety requirements apply where an otherwise-exempt building or extension “receives a cold or hot water supply from a source shared with or located inside” a building that is not itself Schedule 2-exempt. Check the electrical and plumbing arrangement with your building control body before treating an outbuilding or extension as entirely outside the Regulations.

Where approval is needed, there are two separate decisions to make. The first is who acts as your “relevant authority”: GOV.UK confirms “you can either choose your local authority’s building control department or a private registered building control approver.” A registered building control approver takes on the role by serving an initial notice. For sole-trader and small-firm extensions, the Building Safety Regulator’s higher-risk regime will not apply: GOV.UK describes higher-risk buildings as “at least 7 storeys or 18 metres high” and containing “2 residential units”, “a hospital” or “a care home” — well beyond a single-dwelling extension.

For an ordinary local-authority application, the second decision is how you apply: regulation 12 requires anyone carrying out building work to give the relevant authority either “a building notice in accordance with regulation 13” or “an application for building control approval with full plans ... in accordance with regulation 14” — Full Plans or Building Notice, in everyday terms. Full Plans is assessed before you build: GOV.UK states “you can expect a decision within 5 weeks, or 2 months with your consent,” so it suits work you want checked and confirmed before it starts. A Building Notice suits smaller, more straightforward jobs where you’re comfortable starting sooner: GOV.UK states “you can start work 2 days after your notice has been submitted to your BCB,” but nothing has been checked against drawings first, so compliance gets confirmed later, through inspection, rather than agreed up front.

Questions for your building-control provider

Before programming the work, get written answers from your building-control provider on the application route, design evidence, required notices, inspection hold-points, change process and completion document. Keep the answers with the drawing list and inspection programme; re-confirm them if the provider or route changes.

Building Regulations roles are separate too

England's Building Regulations give clients, designers and contractors their own roles and competence duties, including principal designer and principal contractor roles. These are separate from the corresponding CDM 2015 construction-safety roles; the same organisation may perform both if competent, but a CDM appointment alone does not make a Building Regulations appointment. For a business client, where more than one contractor is expected, the client must appoint the Building Regulations principal designer and principal contractor in writing, or certify in writing that the CDM appointees also hold those roles. On a domestic extension, some client management and competence duties pass to the sole contractor or, with multiple contractors, the principal contractor unless the domestic client and principal designer agree in writing that the designer will perform them. If a domestic client makes no principal appointments, the designer and contractor in control of their phases take the respective roles. A business client retains its own client duties.

Complete the records and handover

Completion runs on its own notice-and-certificate cycle. GOV.UK states “you’ll usually get a completion certificate within 8 weeks of completion of the building work, as long as it complies,” and that period is measured from when the authority receives the relevant completion notice rather than simply from the date the work finishes — so give whatever completion notice your building control body requires promptly, rather than assuming the clock starts by itself. The Regulations describe the certificate as “evidence (but not conclusive evidence)” that the relevant requirements have been met, not a document that overrides everything that came before it.

The authority issues the certificate once satisfied, “after taking all reasonable steps,” that the relevant requirements have been met — which means outstanding points from earlier inspections need to be closed out first, not carried forward and hoped past. Don’t commit a client to a fixed certificate date before your building control body has confirmed there’s nothing outstanding; the eight-week figure is what GOV.UK describes as the usual outcome once notice has been given and the work complies, not a turnaround fixed to the day work physically finishes.

Give the client the certificate, or the relevant completion documentation for whichever route you used, and keep an accessible copy alongside the rest of the project record — the submission, the drawings, the inspection notices and any written stage requirements. That documentation is evidence of the building-control history of the work; decisions a future buyer, lender or insurer makes about the property are theirs to make and sit outside the building-control process itself.

If work already went ahead without the required application or notice, regularisation is the retrospective route — available under regulation 18 only for work carried out on or after 11 November 1985, and, as GOV.UK states, “from a local authority BCB only”, not from a registered building control approver. It is an application for the local authority to assess the unauthorised work: regulation 18 lets the authority require you to take reasonable steps to show the work complies, which the regulation allows to include inspecting and testing it, before confirming whether further work is needed and, if satisfied, issuing a regularisation certificate. Submitting the application is not itself an approval, and it doesn’t make previously unauthorised work compliant on its own.