Permitted development


Double dormer extension

Majority of loft conversion projects are classed as permitted development and planning permission is not required. However, there are strict limitations that need to be met:

  • extra space added to the property should not exceed 40 cubic meters on terraced houses and 50 cubic meters on detached and semi-detached properties;
  • attic that belongs to freehold top flat can only be converted within the existing space (dormer construction would require planning permission);
  • loft roof should not exceed the height of the existing front facing roof elevation – i.e. raising of the ridge line is not allowed;
  • materials used for finishing the dormer walls externally should match the appearance of the existing rear elevation;
  • side facing windows should be obscure glazed and 1.7 meters above the finished floor;
  • no verandas, balconies are allowed - only so called Juliette balconies;
  • roof extensions should be set back at least 20 cm away from eaves - this does not apply to hip to gable loft conversions;
  • the property needs to be outside the conservation areas – if the property is in the conservation area, planning permission will be required;
  • building regulations approval and building control inspector visits will be required – after the completion the inspector will issue completion certificate.

In some cases neighbours may object to your project raising the “right to light” issue – when the new extension blocks the natural light getting into their rooms. If you’re unfortunate to get into this position, the size of the extension may be reduced and planning permission may be required – which all takes time and money, let alone the inconvenience and lost added value.

Even if your project surely meets all these criteria, it’s always good to have reassurance – before the actual works take place, apply to your local Council for a Certificate of Lawful Development.

Planning permission

Planning permission for loft extension is required if:

  • the property is within the conservation area;
  • attic to be converted is above the freehold flat – in that case the permission will be granted only for the attic main space conversion, so that’s always a single dormer conversion. Besides, dormer cheeks will need to be positioned away from party walls at a certain distance – thus further reducing the useful space;
  • The newly added space exceeds the maximum allowed cubic meters;
  • The ridge line needs to be raised due to the existing attic low height – however, this is rarely approved.

For more information you can go to this website:

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