Regularisation certificates: approval after the work is done

The rule

(1) This regulation applies where it appears to a relevant authority that unauthorised building work has been carried out on or after 11th November 1985. (3) Where a relevant authority receive an application in accordance with this regulation, they may require the applicant to take such reasonable steps, including laying open the unauthorised work for inspection by the authority, making tests and taking samples, as the authority think appropriate to ascertain what work, if any, is required to secure that the relevant requirements are met.

"Relevant authority" means the local authority, except where section 91ZB of the Building Act 1984 makes the Building Safety Regulator the building control authority (regulation 2). gov.uk puts the practical point plainly: regularisation is available "from a local authority BCB only". Note the date is "on or after" 11 November 1985; gov.uk says "after".

What counts as unauthorised

Regulation 18(8)(a) defines unauthorised building work, where the council is the authority, as building work done without a building notice, without a full plans application, or without the notice of intention to start that regulation 16(1) requires. Work covered by an approver's initial notice is excluded. If an approver's job ended without a final certificate, the route is reversion to the council under the 2024 approver regulations, not regularisation: see missing completion certificates.

How an application works

1. Apply in writing. The owner sends a statement that the application is made under regulation 18, a description of the work and, so far as reasonably practicable, a plan of it and a plan of any extra work needed to bring it into line (18(2)).
2. Opening up. The council may require the work to be laid open, tested or sampled (18(3)). For a steel beam put in to replace a wall, for example, that can mean exposing the ends so the council can see what the beam sits on.
3. The council's answer. It tells you the work it considers necessary, that it cannot determine what is necessary, or that nothing is needed (18(4)).
4. The certificate. Once satisfied that the requirements are met, it "may" give a regularisation certificate (18(5)). The word is may, not must.

Which rules the work is judged against

The standard is "the requirements relating to building work in the building regulations which were applicable to that work when it was carried out" (regulation 18(2)(d)). A kitchen extension built in 2012 is measured against the 2012 requirements, not those in force in 2026. The council must also have regard to any direction dispensing with or relaxing a requirement (18(4) and (5)). It helps to be able to show when the work was done: invoices, dated photographs, the builder's records.

What it costs

Councils fix a "regularisation charge" in their charging schemes under the Building (Local Authority Charges) Regulations 2010 (regulation 5(1)(e)). It is paid when you apply (regulation 8(1)(e)) and is payable by the owner (regulation 2). Councils set charges to recover their costs, so the figure varies from council to council.

A worked example: Bristol City Council's scheme from 1 April 2026 sets the regularisation charge at the total charge, including VAT, for the same work done in advance, but with no VAT added on top. For an extension up to 40 m² that is £700. Any remedial work, the opening up and making good, and any drawings or engineer's calculations the council needs are on top.

Before you apply

• Applying tells the council about the work. Nothing in regulation 18 suspends its enforcement powers, including a section 36 notice within 10 years of completion. If you are selling or buying, speak to your solicitor first, because it may affect indemnity insurance: see missing completion certificates.
• Work before 11 November 1985 cannot be regularised under regulation 18.
• A certificate is evidence, not a warranty. Regulation 18(6) says it is "evidence (but not conclusive evidence)" that the requirements were met.

What this means for you

If you know of unauthorised work, list each item with its date and gather what evidence you can before you apply. Expect some opening up, and budget for the council's charge plus the cost of exposing and making good. Where the council asks for drawings or structural information, have them ready before the inspection.

This guide covers England; Wales has its own version of regulation 18. Parallel Architecture coordinates Building Regulations information as part of its design work, including the drawings a regularisation application needs. Get in touch to talk it through.