What is classed as an extension?
An extension to domestic property is any alteration that increases its overall size. Please note that a conservatory is classed as an extension. Garages, car ports and outbuildings often fall into this category too. A new structure does not need to be actually attached to the house to be classed as an extension, assuming that it is nearer than 5 metres from the house. Anything further than 5 metres from the house tends to classed as a garden structure.
Note that small porches are a special case and are often exempt from planning permission.
Conditions
An extension, enlargement, improvement or other alteration to a house will require permission if at least one of the following circumstances apply:
- Part of the extension lies within 2 metres of the property boundary and exceeds 4 metres in height.
- The cubic capacity of the extension exceeds 70 cubic metres for a detached or semi-detached house or 50 cubic metres for a terraced house. If there are any existing extensions to the original property, then it is the combined cubic capacity of all the extensions that must be included.
- The height of the extension exceeds the highest point of the original dwelling.
- The extension projects beyond the wall of the original dwelling towards a highway, unless the boundary against the highway is over 20 metres away.
- The total ground area of the extension is more than 50% of the ground area within the curtilage of the dwelling.
- The property, or part of the property, is a Listed Building. In this case, Listed Building Consent would be required.
- There is a planning condition attached to a previous permission that restricts permitted development rights.
Please note that the above information applies to houses rather than to flats. Extensions and alterations to flats generally require planning permission anyway.
Calculating Volumes
When calculating the volume of an extension, it is the external rather than the internal volume that is required. Please note all all measurements must be in metric.
As an aid to calculation, the Planning Portal has provided a Volume Calculator.
Further Clarification
In many cases, for small house extensions, it is not always clear-cut whether permission will be required for a given development. The information presented in these pages is not necessarily comprehensive and it is therefore recommended that you speak to a planning officer rather than make the judgement yourself. If in any doubt about whether or not permission is required, please email planning.control@darlington.gov.uk or contact the planning duty officer on 01325 388361.
If you wish to receive a formal letter stating whether or not planning permission is required for your proposed development, you may submit your proposals on a House Extension Enquiry Form. This service is free of charge and is now available online. See Permitted Development Enquiries.
Please note that, if any structural work is involved, Building Control Consent may be required also. This is entirely separate from Planning (see Planning compared to Building Control).