Lawful development certificates — why to get one you do not need

You have checked the limits, your extension falls within permitted development, and you do not need planning permission. Good — that saves you eight weeks and several hundred pounds.

Now apply for a certificate saying so anyway.

What it is

A lawful development certificate is a formal decision from the council confirming that a specific proposal does not require planning permission. There are two kinds: one for proposed work, and one for something already built.

It is not planning permission. It is the council examining your drawings against the permitted development rules and issuing a document that says: this is lawful.

It costs half a full planning application fee, and takes roughly the same eight weeks a householder application would.

Why bother, if the work is lawful either way

Because “lawful” is a conclusion somebody has to reach, and without the certificate the only person who has reached it is you.

When you sell. This is the big one. A buyer’s solicitor asks what authorisation exists for the extension. “It was permitted development” is an assertion. A certificate is evidence. Without one, buyers’ solicitors commonly require indemnity insurance, ask for a retention, or in awkward cases advise the buyer to walk. Sales fall through over exactly this, at the point where you have least leverage.

Because permitted development is more complicated than it looks. The rules turn on things people get wrong routinely:

• “Original house” means as it stood on 1 July 1948, or as first built if later — not as you bought it. A previous owner’s extension counts against your allowance and you may not know it exists.
• The 50% curtilage rule counts every building other than the original house. Sheds, a garage, an old conservatory.
• Designations remove rights. In Horsham District that means 39 conservation areas, three Article 4 directions, the South Downs National Park and the High Weald National Landscape.

Any one of those can mean a project you were confident about was not permitted development at all.

Because enforcement has a time limit, and you want to prove you are past it. There are time limits after which the council can no longer take enforcement action against unauthorised building work. But relying on the clock means relying on being able to prove, years later, exactly when work was completed. A certificate obtained at the time removes the question.

The certificate for work already done

If you have already built something and never got a certificate, you can apply for one retrospectively — a certificate of lawfulness of existing use or development.

The burden of proof is on you, and it is evidential rather than judgemental: dated photographs, invoices, delivery notes, statutory declarations from people who saw the work. The council is not deciding whether it likes the extension; it is deciding whether you have shown it was lawful, or has become immune from enforcement through the passage of time.

This is much harder than applying before you build, which is the argument for doing it in the right order.

What you need to apply

Broadly the same drawings as a planning application:

• Location plan and block plan
• Existing and proposed floor plans and elevations, to scale
• A written statement setting out which class of permitted development you are relying on and how the proposal complies with each limit

That last item is the one that matters. A certificate application is a legal argument, not a design proposal. You are not asking the council whether they like it — their opinion of the design is irrelevant. You are demonstrating that it falls inside the rules.

Where it does not help

A certificate confirms that a right exists. Where the right has been removed there is nothing to certify.

If you are in Slinfold Conservation Area, where an Article 4 direction has removed the extension right entirely since 1997, no certificate is available for an extension — you need a full planning application. The same applies to the named Denne Road properties in Horsham.

The honest cost comparison

• Do nothing: free now. Possible cost later — indemnity insurance, a price reduction, a delayed or collapsed sale.
• Certificate: half a householder application fee, plus drawings you probably need anyway, and about eight weeks that can run in parallel with building regulations and party wall notices.
• Full planning application: £548 and eight weeks, with the council able to refuse.

If the drawings exist and the eight weeks overlaps with something else you are waiting for, the certificate is close to free in practical terms.

What to do next

If you are relying on permitted development, get the drawings done properly and apply for the certificate at the same time as you serve party wall notices and submit building regulations. All three run in parallel; none of them is on your critical path if you start them together.

Tell us what you are planning and we will tell you which route it is on before you spend anything.