Permitted development covers more than most homeowners expect - and less than many hope. A plain-English guide to where the line sits.
This is the first question almost every extension client asks, and the honest answer is: probably not, but it depends on several things that are worth checking before you spend money on drawings.
What permitted development allows
For a detached house, a single storey rear extension can generally project up to four metres under permitted development. For a semi-detached or terraced house, that figure is three metres. Under the larger home extension scheme those limits extend to eight and six metres respectively, subject to a prior approval process where neighbours are consulted.
Height matters too: a maximum of four metres overall, and no higher than three metres if the extension sits within two metres of a boundary. Eaves height within two metres of a boundary is capped at three metres.
Where permitted development does not apply
Several situations remove permitted development rights entirely:
- Flats and maisonettes have no permitted development rights for extensions.
- Listed buildings require listed building consent regardless of size.
- Conservation areas, National Parks and Areas of Outstanding Natural Beauty carry tighter restrictions, particularly on side extensions.
- Some properties, especially on newer estates, have had permitted development rights removed by a condition on the original planning permission or by an Article 4 direction.
That last one catches people out regularly. It is worth checking the original planning decision notice for your property before assuming anything.
Get a lawful development certificate anyway
Even when your extension clearly falls within permitted development, apply for a Lawful Development Certificate. It costs a fraction of a full planning application and gives you formal written confirmation from the council that what you have built is lawful.
When you come to sell, your buyer's solicitor will ask for it. Producing a certificate is straightforward. Explaining that you were fairly sure it was permitted development is not.
Building regulations are separate
This is the point most commonly misunderstood. Planning permission and building regulations are two entirely different approvals. Even a fully permitted-development extension needs building regulations approval covering structure, insulation, drainage, fire safety and ventilation.
Skipping it does not save time or money. It creates a problem that surfaces at exactly the worst moment - during a sale.