Can you sell a house with an extension without planning permission?

There's no law against selling a house with unauthorised work, but the conveyancing process is designed to find it. Buyers' solicitors compare what's built against the planning history, and mortgage lenders take an interest too — an unexplained extension can stall a chain at exactly the wrong moment.

The cleanest fix depends on the facts. If the extension was within permitted development, or has been in place long enough to be immune from enforcement — 4 years if substantially complete before 25 April 2024, 10 years for later work — a Lawful Development Certificate turns the grey area into formal proof.

Where the work is recent and did need permission, a retrospective application can regularise it before listing, though it takes the standard 8 weeks and carries genuine refusal risk if the extension wouldn't have been approved in the first place.

Indemnity insurance is the pragmatic middle road many sales take: a one-off premium covering the buyer against enforcement costs. It's quick, but it's a patch, not a cure — the policy is invalidated if the council is alerted, so you can't apply for permission afterwards, and the underlying question just passes to the next owner.

Don't forget building regulations. Even a planning-clean extension needs building control sign-off, and a missing completion certificate raises the same conveyancing flags with its own separate fixes. Sorting both regimes before you market the house protects the price far better than negotiating under offer.