For a single-storey side extension
The following permitted development restrictions apply to all extensions and alterations to a dwellinghouse:
- Residential properties created as a result of prior approval (e.g. change of use from office to residential) do not benefit from householder permitted development rights. All new extensions will therefore require planning permission.
- No more than 50% of the curtilage of the dwelling should be covered by buildings or extensions (excluding the original dwelling).
- No extension should exceed the height of the highest part of the roof of the existing dwelling.
- The eaves height of the extension should not exceed the eaves height on the existing dwelling.
- If the extension is within 2 metres of your boundaries, the eaves height should not exceed 3 metres high;
- The extension should not include or incorporate a veranda, balcony, raised platform, microwave antenna, chimney, flue or soil and vent pipe or alterations to any part of the roof of the dwelling.
- If the property is in on Article 2(3) land, i.e. situated within a National Park, an Area of Outstanding Natural Beauty, a Conservation Area, an area designated under s41(3) of the Wildlife and Countryside Act 1981, the Norfolk Broads or a World Heritage Site, no part of the original or extended house should be clad in stone, artificial stone, pebble dash, render, timber, plastic or tiles.
- Unless it is a conservatory, the extension should be built using external materials similar in appearance to those on the existing house;
Single-storey side extensions will not require planning permission provided they also comply with the following criteria:
- The proposed side extension would not be located between the house and a highway, i.e. if the house is on a corner plot and an extension is proposed on the side facing the highway then planning permission is required.
- The extension would be single storey in height and no more than 4 metres high.
- The extension would exceed half the width of the original dwelling. On a detached house, provided the plot can accommodate them, it is possible to build a “half-width” single-storey extension on each side
See also Property Alteration Overview for more potential restrictions: https://planningaid.zendesk.com/hc/en-us/articles/203210341-Property-Alterations-Overview