Rules on extensions to houses

Extending a home is a great way to add extra space to your home without having to move but can seem a bit daunting when you first start looking into it! So much new terminology and things to consider outside of what you want your dream extension to look like.

Yoop Architects will submit and manage any planning approvals/regulations/agreements on your behalf and chase them up until we get the OK so you don’t have to worry about them but if you’d like to know more about what’s involved, read on…

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Yoop Architects will submit and manage any planning approvals/regulations/agreements on your behalf and chase them up until we get the OK so you don’t have to worry about them

Planning Permission
Planning permission may not be required for your extension if the changes you are making are within the rules of permitted development. If you’re not covered by permitted development (see below) then you can apply for planning permission via or through your local authority. An application in England for an extension currently costs £206.

Permitted Development
Permitted development means that as long as your house is quite original and unmodified, then you’re allowed to do various minor changes to your house without planning permission. No need to inform anyone – you can just build it. There are a few reasons why you should still submit an application but you don’t need approval. A Certificate of Lawfulness (what you will receive when you submit an application for permitted development) currently costs £103.

What is covered by permitted development?

Single Storey

  • The extension must be at the rear of the property – if the extension involves building out towards a main road, you may require planning permission
  • Single storey rear extensions can be built up to three meters from the original rear of the house if it’s a terraced or semi-detached property or four metres if it’s a detached property
  • Single storey rear extensions cannot exceed a height of four metres
  • No more than half the area of land around the original house can be covered by extensions or other builds. This includes sheds and other outbuildings
  • Materials must be in-keeping with your property’s current appearance, unless you’re building a conservatory

Multiple Storey

  • Multiple storey rear extensions can be built up to three meters from the original rear of the house (same for attached/detached properties)
  • You can achieve a double storey rear extension of up to three meters on the ground floor and three meters on the first floor, but all of the extensions need to be at least two meters away from each boundary
  • The eaves (the part of a roof that meets or overhangs the walls of a building) and ridge height of the extension can’t be higher than the existing house
  • Two-storey extensions have to be a minimum of seven metres away from the rear boundary
  • The roof pitch (angle) must match the existing house, or be as close as possible

Side Extension

  • Single storey, side extensions cannot exceed a height of four metres and mustn’t have a width of more than half that of the original house
FREE GUIDE: Category: Planning Permission
FREE: Complete Guide to Planning Permission for Homeowners

Inside this easy to read free guide, we will teach you the key things you need to know about planning permission.

Loft Conversion
Generally, Room Loft Conversions, Dormer Loft Extensions and Hip to Gable Roof Extensions can be achieved under permitted development as long as the extension complies with the following limits and conditions:

  • A volume allowance of 40 cubic metres additional roof space for terraced houses
  • A volume allowance of 50 cubic metres additional roof space for detached and semi-detached houses
  • No extension beyond the plane of the existing roof slope of the principal elevation that fronts the highway
  • No extension to be higher than the highest part of the roof
  • Materials to be similar in appearance to the existing house
  • The roof enlargement cannot overhang the outer face of the wall of the original house

(Source –

Garage/Basement Conversion
Converting an existing basement/garage into a usable living space does not require planning permission and will be covered by permitted development (unless your home is in a conservation area or is a listed building)

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Building Regulations Approval
The Building Regulations are minimum standards for design, construction and alterations to virtually every building to ensure the safety and health for people in or about those buildings.

All extension work requires building regulations approval and you may need building regulations approval for many alteration projects. However, you do not need to get approval yourself if you use someone registered with a competent person scheme.

Shared Drains
If you’ve got a shared waste pipe running across the back of your garden and you’re going to build over it or within three meters proximity, you’ll need to submit a Build Over Agreement to the Water Authority. A Build Over Agreement costs £335 pounds with Thames Water.

Shared Walls
If your extension involves building or digging foundations within 3m of a party (shared) wall or other foundations, the work will require you to comply with the Party Wall Act. A Party Wall Award (Agreement) will protect you and your neighbour if anything goes wrong.

Now that you know more about the rules and regulations of building an extension, your next step would be to speak to an architect who can help you source and liaise with a local planner. Go ahead and book a free call below with Yoop.


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