Does my extension need planning permission? A plain-English guide for East Sussex & Kent homeowners

Not every extension needs planning permission. The government's permitted development (PD) rules — set out in the GPDO 2015 — let you do a fair amount without applying, as long as you stay inside the limits. Here's the plain-English version for homeowners across East Sussex and Kent.

Often permitted development (within limits)

• Single-storey rear extensions — up to set depth and height limits (larger ones may need a “prior approval” notification rather than a full application).
• Side extensions — single storey, limited width and height.
• Loft conversions and rear dormers — within volume limits (front-facing dormers usually aren't PD).
• Outbuildings — sheds, garden rooms and home offices, within height and coverage limits.

Usually needs planning permission

• Anything over the PD size/height limits.
• Front extensions and most work forward of the principal elevation.
• Two-storey extensions beyond the limited allowances.
• Work to a flat, a maisonette, or a listed building (listed buildings also need listed building consent).

The local rules that change the answer

This is where East Sussex and Kent homeowners get caught out. Your PD rights can be reduced or removed if your home is in a:

• Conservation area — tighter limits (e.g. side extensions and some cladding lose PD).
• The High Weald National Landscape (AONB) — covering much of Rother, Wealden and Tunbridge Wells — where certain PD allowances are restricted.
• Area with an Article 4 direction — the council has removed specific PD rights for that street or area.

Always check your specific address before assuming.

“Permitted” — so do nothing? Not quite.

Even when your project is permitted development, it's worth getting a Lawful Development Certificate (LDC). It's a formal confirmation from the council that your work is lawful — invaluable when you come to sell, and proof if a neighbour ever questions it. If your project is close to the limits or needs prior approval(like a larger rear extension), you'll want the right supporting statement for that too.

The quick way to know

Buildwise runs a free permitted development checkagainst the GPDO 2015 for your postcode — extensions, lofts, outbuildings and more — and detects local constraints like conservation areas automatically. If you're permitted, it can generate your LDC supporting statement; if you need prior approval or full permission, it produces the right document for that instead.

Check your project free — run a PD check →

Frequently asked questions

• How big can a rear extension be without planning permission? Single-storey rear extensions are permitted within set depth and height limits; larger ones may qualify under the “larger home extension” prior-approval route. Limits are tighter in conservation areas.
• Do I need permission for a garden room or home office? Often no, if it stays within outbuilding height and coverage limits and isn't used as a separate dwelling — but AONB and conservation-area rules can change this.
• What is a Lawful Development Certificate? A formal council confirmation that your work is lawful permitted development. Not compulsory, but strongly recommended — especially before selling.
• How do I know if my home is in a conservation area or the High Weald National Landscape? A permitted-development check that reads your postcode will flag it; or check your council’s online mapping.

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