• Home Page
• -
• Environment
• -
• Planning and building control
• -
• Planning advice 2

Dormer extensions

The following advice is intended for guidance only and assumes that permitted development rights have not been withdrawn by either condition or an Article 4 Direction. If permitted development rights have been removed you will need to submit a planning application for consideration.

To find out if you need planning permission for any of the above developments, answer the questions below:

1. Is the dwelling within a conservation area or is the building to be extended, listed or of architectural or historical interest?
   
   Yes - planning permission is likely to be required and you should contact planning services on 443 2381 before starting any work.
   No - go to question 2.
   
2. Will the extension involve building higher than the highest part of the existing roof?
   
   Yes - planning permission is required.
   No - go to question 3.
   
3. Will the proposed dormer be constructed on a roof slope that faces a road, pavement or public footpath?
   
   Yes - planning permission is required.
   No - go to question 4.
   
4. (a) In the case of a terraced dwelling will the cubic content of the proposed dormer exceed 40 cubic metres?
   
   Yes - planning permission is required.
   No - go to question 5.
   
   (b) In the case of other dwellings will the cubic content of the proposed dormer exceed 50 cubic metres?
   
   Yes - planning permission is required.
   No - go to question 6.
   
5. In the case of a terraced dwelling will the cubic content of the proposed dormer, when added to the volume of any other previous extension to the house, exceed 50 cubic metres or 10 per cent of the original volume of the house, whichever is the greater subject to a maximum of 115 cubic metres?
   
   Yes - planning permission is required.
   No - planning permission is not required.
   
6. In the case of other dwellings will the cubic content of the proposed dormer, when added to the volume of any other previous extension to the house, exceed 70 cubic metres or 10 per cent of the original volume of the house whichever is the greater subject to a maximum of 115 cubic metres?
   
   Yes - planning permission is required.
   No - planning permission is not required.
   
   Note: The cubic content of any previous extensions or dormers that are to remain should be included in your calculation since they count against the allowance.
   
   Cubic content is an external measurement calculated by multiplying length by width by height and must include all of the structure including the roof.