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Local Planning Guidance Note (LPG) No 20 - House Extensions

This is one of a series of Local Planning Guidance notes amplifying Development Plan proposals in a concise format. The guidelines which follow have been prepared and adopted by the County Borough Council to inform prospective house owners, builders and agents about the issues relating to house extensions, and to encourage a better standard of design. If you have any queries, a planning officer will be pleased to discuss your proposals before you make an application. You may also wish to talk to your neighbour(s) to let them know what you are proposing to do.

The Development Plan stresses that generally house extensions will be permitted, providing that they reflect and enhance the appearance of the existing property, adjoining properties, and their setting in terms of scale, design and materials. However, there are a substantial number of detailed issues that need to be taken into account in designing domestic extensions. Listed buildings and older properties in conservation areas usually require special consideration, and specific advice can be given on request by the planning department.

Your house and garden

The following points should be borne in mind:

Your house and your neighbour's house

The 45o Test

This is guidance only and passing the test does not mean automatic approval, nor the reverse.

Side extensions - specific guidelines

Where the property stands in a line of detached/semi detached dwellings and the extension would fill in the gap, there is a risk that the extension will create a terraced appearance. This is not always in the interests of maintaining the character of the street, and, in the interests of visual amenity, should be avoided. One way of maintaining a visual break would be to set back the extension behind the front of the dwelling by a metre to create a clear break.

The following criteria should be met:

Great care is needed in the design of extensions on corner plots, which often provide an open appearance and greenery, and are prominent from both streets. The following criteria for corner plots should be met:

On side plots there can be problems in incorporating the minimum parking standards. Where proposals involve access, garages or car ports, the following criteria should be met:

Rear extensions - special guidelines

Rear extensions, including conservatories, should not dominate, nor materially alter, the existing levels of sunlight, privacy and daylight to adjoining properties.

Two storey rear extensions should not come nearer than 2 metres of a boundary that forms a party wall between terraced and semi-detached properties and 1 metre of other boundaries. The maximum projection from the dwelling should be one third of the garden width. Proposals should satisfy the 45o test.

Any extensions within one metre of the boundary will normally be limited to a maximum of 3.5 metres in length. For every additional metre from the boundary this can be increased by one metre.

Front extensions - specific guidelines

Front extensions will clearly impact on the street scene and will rarely be acceptable. Front extensions must be sympathetic to the form, scale, proportion and design of the dwelling and neighbouring properties, and should not:

It is sometimes possible to construct some porches without the need for planning permission. Whether they require planning permission or not, they should match the character and design of the existing property and should:

Roof extensions - specific guidelines

Roof alterations and dormer windows should be kept as small as possible so as to minimise the visual impact on the appearance of the property and the surrounding area, and to minimise the loss of privacy to neighbours. The following criteria should be met:

Updated March 2010