Lawful Development Certificates

A lawful development certificate is not planning permission. It is the opposite of one: a formal determination by the council that for this particular piece of work, on this particular property, no permission is required. That distinction sounds academic until something goes wrong, at which point it turns out to be the whole point of the document. This guide covers the two kinds of certificate, what each one proves, what it does not protect you from, and the one place people ask for the wrong one at exactly the wrong moment.

Two certificates, and they are not interchangeable

One is for work you intend to do. The other is for work that is already standing.

The Town and Country Planning Act 1990 provides for both, and they are separate applications with separate evidence behind them. A certificate for proposed development is applied for before you build, and asks the council to confirm that what you have described would be lawful if carried out. A certificate for existing development is applied for after the fact, and asks the council to confirm that something already built, or a use already established, is lawful now.

Asking for the wrong one is a wasted fee. If the extension is up, a proposed certificate is meaningless. If it is not, there is nothing existing to certify.

Why “not permission” is the whole point

The council is not judging your extension. It is answering a question of fact and law.

On a planning application the officer weighs the scheme against policy and forms a planning judgement. On a certificate application there is no judgement to form. The council is deciding whether the thing you have described falls inside the rules, and if it does, the certificate must be issued whether or not anybody at the council likes the design.

Several consequences follow from that, and they are all useful. There is no neighbour consultation, because a neighbour’s opinion is not a fact about the planning rules. Character, appearance and amenity are irrelevant. The officer cannot impose conditions, because there is no permission to attach them to. And the burden of proof sits with you rather than with the council, on the balance of probabilities, which is not how a planning application works at all.

A refusal means the council does not accept that what you have described is lawful. It is not a ban. The next step is usually to apply for permission, to redesign so the work genuinely does fit the rules, or to appeal the refusal, which is an argument about fact and law rather than about planning merits.

The proposed certificate: the description is the certificate

What is protected is the thing you described, at the dimensions you gave.

A certificate for proposed development conclusively establishes the lawfulness of the development described in it. That word described is doing an enormous amount of work. The certificate attaches to the description and the drawings behind it, not to your extension in general, so every dimension a rule turns on has to be on the drawing and has to be right.

That means the depth measured from the original rear wall rather than the current one, the overall height, the eaves height where the extension comes near a boundary, the distance to the boundary itself, the materials, and the position relative to the walls the rules care about. The relevant limits and the conditions sitting beside them are set out in permitted development rights for extensions. A certificate obtained on a drawing that the finished extension does not match is worth close to nothing, and building 300 millimetres deeper than the drawing said is enough to break it.

There is a second limb people rarely notice. The conclusive effect of a proposed certificate can be undermined by a material change, before the work begins, in any of the matters relevant to its lawfulness. If an Article 4 direction is made over the area after your certificate is issued but before you start, or the underlying rules are amended, the ground can move under you. Certificates for proposed work are not a licence to sit on a scheme for years.

And a certificate can be revoked. Where one has been obtained on a false statement, a false document or by withholding material information, the council can cancel it, and knowingly making a false statement in that context is a criminal offence rather than a civil embarrassment.

The existing certificate: evidence, and the ten year line

Two quite different arguments arrive under the same heading.

The first argument is that the work was permitted development when it was carried out, so it never needed permission. That turns on the rules and on what the house looked like at the time, which usually means establishing what had already been added before it.

The second argument is immunity. Unauthorised work becomes lawful once the council can no longer take enforcement action against it, and a certificate is how that gets recorded formally. For building work in England the enforcement time limit is now ten years, following a change that took effect in April 2024. Work substantially completed before that change keeps the shorter four year limit that applied at the time, so which side of that line an old extension falls on decides whether it is already immune or has years still to run. Establish the date before anything else.

Evidence is the whole of an existing-use application, and the council will test it rather than take it on trust. What carries weight is anything contemporaneous and dated: photographs with a verifiable date, builders’ invoices, delivery notes, bank records, council tax or utility records, estate agents’ particulars from an earlier sale, and aerial or street level imagery. Statutory declarations from people who remember the work are used routinely, and they are stronger when they corroborate documents rather than stand alone. Uncontradicted evidence of sufficient precision will normally succeed.

Deliberate concealment is the exception to all of it. Where a breach has been actively hidden, the council can apply to a magistrate for an order that restarts the clock, and the courts have shown little sympathy for people who built something and covered it up while the years ran.

The conveyancing trap

Asking the council about an old extension can destroy the cheaper way of dealing with it.

Where an extension has no paperwork and a sale is imminent, there are broadly two routes. One is to apply for a certificate and get the position settled properly. The other is an indemnity policy, which insures the buyer against the consequences of enforcement rather than resolving anything.

Those two routes do not sit comfortably together. Indemnity policies are generally unavailable, or void, once the local authority has been approached about the matter, because the insurer is pricing the risk that nobody has drawn the council’s attention to it. A well meant phone call to the planning department on a Friday afternoon can therefore remove an option that would have cost a fraction of the alternative.

Neither route is automatically right. A certificate is the better answer where the work is genuinely old and the evidence is good, because it settles the question permanently rather than papering over it. Take advice on the order of operations before contacting anybody, and treat that as the first step rather than the last.

It is not the same document as a completion certificate

Different regime, different team, different piece of paper.

A lawful development certificate answers a planning question. A Building Regulations completion certificate answers a construction one, and every extension needs the second regardless of the planning position. They are issued by different parts of the council, on different applications, and a buyer’s solicitor will typically want both. The building control side is covered in what a completion certificate is.

Keep whichever certificates you end up with alongside the deeds. Ten years later, nobody involved will remember which route the extension took, and the file is the only thing that does.

What a certificate does not cover

It answers one question, cleanly, and no others.

It is not listed building consent, which is a separate regime under separate legislation where unauthorised work is a criminal offence. It says nothing about Building Regulations. It has no effect on the Party Wall etc. Act 1996, which is triggered by what you are doing to a shared wall or near a neighbour’s foundations rather than by whether permission was required. It does not touch restrictive covenants on your title, which the council never looks at, and it will not save you from felling a protected tree.

Nor does it cover work you have not described. Where a project involves an extension plus a rooflight plus an outbuilding, each sits under its own part of the rules, and the application needs to describe all of it.

What goes in, and what deliberately does not

A certificate application is thinner than a planning application, and the thin parts are the point.

You submit the form, a site location plan, existing and proposed drawings to a proper scale, a precise written description of the development, and the fee. On an existing-use application the evidence goes in as well, indexed rather than piled up, with a statement explaining what each document proves and when.

What is absent is everything a planning application uses to persuade. No design and access statement, no heritage statement, no argument that the extension is in keeping or that the family needs the space. None of it is relevant, and including it invites an officer to start thinking in planning terms about an application that is not a planning application. The one thing worth adding is a short note setting out, rule by rule, how the proposal satisfies each condition of the relevant class. It makes the officer’s job mechanical, which is exactly what you want.

When it is worth applying

Nearly always, on proposed work, and the reason is the sale rather than the build.

Permitted development produces no paperwork. There is no application, no decision notice and nothing on the public file, so an extension built entirely lawfully leaves no trace that it was. The certificate is what fixes that, and its fee is modest against what it protects.

It is worth applying where you are relying on permitted development at all, where the house has been extended before and the remaining allowance is finely balanced, where you intend to sell within a few years, and where anything about the property is unusual enough that a future conveyancer will ask. It is not worth applying where you already hold planning permission, because the decision notice does that job.

The determination period is the same statutory eight weeks as a householder application and it runs from validation rather than from submission, so the drawings still have to be right first time.

We establish the route at the survey, before anything is drawn, and where the answer is permitted development we treat the certificate as part of the job rather than as an optional extra. It costs a small amount now and it answers a question that would otherwise be asked at the worst possible moment.

Enforcement time limits, fees and statutory periods are revised from time to time, and whether any particular piece of work is lawful depends on the property, its planning history and the dates involved. Treat this as an explanation of how certificates work rather than as confirmation of your own position.

Last reviewed August 2026. Planning and Building Regulations change, and your property may differ.