Skip to content
All guides
Extension5 min read · Jun 2026

The seven planning pitfalls that delay home extensions

Single-storey rear extensions and side-returns mostly fall under permitted development. Here's the short list of things that quietly knock you out of it.

The seven planning pitfalls that delay home extensions

The seven that catch people out

  • Article 4 directions — some councils remove permitted development rights street-by-street. Check before you design.
  • Conservation areas & listed buildings — PD is curtailed or gone; expect full planning and conditions.
  • Depth limits — rear extension depth allowances are finite and the larger-home prior-approval route has a neighbour-consultation step.
  • Height & eaves — exceeding the eaves/ridge rules near a boundary fails PD instantly.
  • Side returns on the boundary — a Party Wall Act notice to the neighbour is separate from planning and adds weeks.
  • Previous extensions — earlier additions count against your remaining PD allowance.
  • Flats & maisonettes — permitted development for extensions generally doesn't apply.

Do this first

Get a Lawful Development Certificate if you're relying on permitted development — it's proof, not a formality, and a buyer's solicitor will ask for it later.

Budget the Party Wall surveyor and building-control fees as line items, not afterthoughts.

Ready to put this into practice?

Tell us about your project and let verified builders bid for it — or check any builder by their CB number.