Loft Conversion Planning Permission

Most types of loft conversion do not require planning permission and can be achieved via permitted development, as long as the extension complies with the following limits and conditions:

(Source –

  • 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
  • No verandas, balconies or raised platforms
  • Side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor
  • Roof extensions not to be permitted development in designated areas**
  • Roof extensions, apart from hip to gable ones, to be set back, as far as practicable, at least 20cm from the original eaves
  • The roof enlargement cannot overhang the outer face of the wall of the original house.

*Bear in mind that any previous roof space additions must be included within the volume allowances listed above. Although you may not have created additional space a previous owner may have done so.

**Designated areas include national parks and the Broads, Areas of Outstanding Natural Beauty, conservation areas and World Heritage Sites.

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Types of loft conversions that are usually exempt from planning permission and achieved via permitted development

Room Loft Conversion
A room loft conversion is where you board out the loft and add a staircase. Maybe add a few skylight windows in the slope of the roof. You would require a good sized loft with good head height.

Prices start from £15,000

Dormer Loft Extension
A dormer loft extension is where a big box is typically added to the rear of the roof. This gives lots more space. Typically created via permitted development.

Prices start from £20,000 or from £35,000 with the inclusion of an en suite

Hip to Gable Roof Extension
A hipped roof is when all four sides of the roof slope in towards the middle. The loft space is not very good. A gabled roof is like a roof of a terraced house – two sides of the roof slope and the other two sides have a wall which go all the way up to the ridge (top of the roof). The gable roof is good for loft extensions.

There is a permitted development where you can do a hip to gable extension – usually on a semi detached property. Councils do not like this type of development as it will unbalance a semi detached pair but if done correctly at permitted development, the council can not stop it.

Prices start from £25,000

If your extension exceeds the limits and conditions set out in the permitted development legislation, then you will require planning permission.

Types of loft conversions that usually require planning permission

‘Raising the Roof’ or Changing the Roof Structure
If the head height is not enough, altering the roof can be achieved via planning permission but can be difficult. The planners may suggest it will be incongruous to the original house as it may look different to the adjacent housing. Where it maybe possible is when houses are on a sloping street and ridge heights are not related to each other. Can be costly as it required a new roof.

Prices start from £40,000


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