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Class AA - Extensions and Alterations to Your House

Class A of the General Permitted Development Order (GPDO) covers most single-storey and two-storey extensions, as well as alterations and improvements to the main house. It’s the rulebook people usually turn to when asking: “Can I build an extension without planning permission?”

Our easy guide sets out what you can and can’t do with these rights. Scroll down for a quick reference table, and the full legislation is included at the bottom of the page for reference.

⚠️ Before you start

  • Class A applies only to houses — not flats or maisonettes.


  • Your rights may have been removed (for example, by an Article 4 Direction or a condition on a past planning permission).


  • Even if your extension is PD, you still need to comply with Building Regulations and may need a Party Wall Agreement.


✅ What you can do under Class A:

  • Build a single-storey rear extension up to:


  • 3m deep on a terraced or semi-detached house.


  • 4m deep on a detached house. (In some cases, up to 6m / 8m depth with the “larger home extension” prior approval process).


  • Build a two-storey rear extension up to 3m deep, provided it is at least 7m from the rear boundary.


  • Extend up to 50% of the curtilage (the land around your house), including outbuildings.


  • Increase height up to the main ridge/eaves, as long as the extension isn’t taller than the house.


  • Use materials of a similar appearance to the existing house.


  • Add new windows, doors and rooflights (with restrictions for side-facing windows).


❌ What you can’t do under Class A:

  • Build beyond the principal front elevation or a side wall facing the highway.


  • Exceed 4m in height for single-storey extensions.


  • Go within 2m of the boundary with eaves higher than 3m.


  • Add balconies, verandas or raised platforms.


  • Use cladding on houses in conservation areas or other sensitive “article 2(3)” land.


  • Build two-storey rear extensions in conservation areas, National Parks, AONBs or similar protected areas.


Things to check...

Has your property already been extended? The 3m/4m allowance applies to the original house (as built in 1948 or when first constructed if later). Previous extensions count towards the limit.

Are you in a conservation area or other designated land? Restrictions are tighter.

Will your extension affect neighbours? Larger home extensions (over 3m / 4m) require prior approval, meaning your council notifies neighbours and considers amenity impacts.

Summary

Class A rights allow many common extensions without full planning permission — but they come with detailed limits. If your proposal falls outside these rules, you’ll need a householder planning application.

👉 If you’re unsure whether your extension qualifies under Class A, or if your home has restrictions in place, get in touch and I can guide you through your options.



Class A - The Legislation