Do I need planning permission?

Design Ideas
Home & Maker Thu Jul 21 2022 01:00:00 GMT+0100 (British Summer Time)

Every project is different but they all have to follow the same rules set by the government. Sometimes you need permission to build, and sometimes you don't.

Understanding whether you need planning permission or not begins with a set of defined rules known as ‘Permitted Development' rights, that allow you to extend a house without needing to apply for planning permission, if specific limitations and conditions are met. We do advise gaining a lawful development certificate that proves to your local authority and future buyers that your build was lawful at the time of construction - you can find this service in our Extension or New Home cost calculators.

You can build more than you realise under Permitted Development so take a look at this quick checklist to see if your project falls into one of the classes of Permitted Development:

  • Enlargement, improvement or alteration – Class A
  • Additions to the roof – Class B
  • Other alterations to the roof – Class C
  • Porches – Class D
  • Outbuildings – Class E
  • GPDO 2015 Permitted Development Class
  • Normal Areas Conservation Areas
  • Single Storey Rear Extensions A A (Extra Restrictions)
  • Two Storey Rear Extensions A Not Permitted
  • Side Extensions A Not Permitted
  • Loft Extensions B Not Permitted
  • Roof Lights C C
  • Basements A A
  • Porches D D
  • Outbuildings E E (Extra Restrictions)
  • Patios F F
  • Chimneys G G (Extra Restrictions)

These quick checklists should start to give you an idea if your idea falls under Permitted Development (PD). If you can check off each item for your kind of project, then there is a good chance that you don’t need planning permission and you are well informed to begin your building journey!

Single Storey Rear Extensions

Single storey rear extensions can be built in Class A of the GPDO. A rear extension is the most common householder PD project.

  • Max height 4m
  • Max height 3m if within 2m of any boundary
  • Extension depth max 4m (or up to 8m until May 2019) if detached house
  • Max extension 3m (or up to 6m until May 2019) if semi-detached or terraced house
  • Note : No cladding in Conservation Area 

Two Storey Rear Extensions

Two storey rear extensions can be built in Class A of the GPDO. You need to make sure that there is a big enough gap to the boundary to meet the rules.

  • Max height to match existing house
  • Height max of 3m, if within 2m of any boundary
  • Max extension from rear wall of 3m
  • Side windows fixed and obscure glazed to 1.7m above floor level
  • Not in Conservation Area

Side Extensions

Side extensions can be built in Class A of the PD rules. They are only allowed to be one storey and are not allowed in a Conservation Area.

  • Max height of of 4m
  • Single storey only
  • Max width 50% of original house
  • Not in Conservation Area
  • Roof Extensions
  • Roof extensions,like dormer windows or hip-to-gable conversions, can be built in Class B of the GPDO.
  • Max height of dormer or loft extension to match existing roof
  • Max increase in loft volume of 50m3 (40m3 for terraced house)
  • Eaves retained and extension set in 200mm
  • Side windows fixed and obscure glazed to 1.7m above floor level
  • No extension forward of original front roof slope
  • Not in Conservation Area

Roof Lights

Roof lights can be built in Class C of the PD rules. They can be built on any roof slope, including the front, and are even allowed in Conservation Areas.

  • Max protrusion 150mm above roof slope
  • Roof lights on side roof slopes fixed and obscure glazed to 1.7m above floor level


A Porch can be built at any entrance door under Class D of the GPDO 2015.

  • Max external area of 3m2
  • Max height of 3m
  • Not within 2m of boundary with highway


Outbuildings, such as sheds, garden rooms or garden offices, can be built in the curtilage of the property as Class E Permitted Development.

  • Max roof height of 4m, reduced to 2.5m if within 2m of boundary
  • Max eaves height of 2.5m
  • Must not be used as a separate house
  • Not built in front of house, and not at side of house if in Conservation Area
  • Patios*

A patio, decking or other hard surface, such as a driveway, can be built under Class F of the PD rules.

  • Must be made of porous material, if at front of house
  • Must not be a raised more than 300mm


Chimneys or flues can be built or taken down under Class G of the GPDO.

  • Max height of 1m higher than existing roof
  • Not on front or side roof pitches facing road in Conservation Area
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