A Guide to House Extensions

General Principles

The council encourages good design when considering applications for domestic extensions. Well designed extensions improve the appearance of a house as well as making a positive addition to the street scene.

As a general rule, well designed extensions will:

  • be subordinate to and not dominate the original house
  • be in keeping with the general design of the other properties in the street
  • have carefully designed roofs which reflect the pitch and style of the existing
  • respect the privacy and outlook of neighbours
  • use windows and doors which reflect the proportions of, align with and are similar to the originals
  • use materials that match the original
  • do not create an unacceptable imbalance with the adjoining house in the case of semi- detached and terraced properties.

Planning permission will not be granted for poorly designed extensions.

Front and Side Extensions

Front and side extensions will be seen from the street and their design is important, especially side extensions on corner plots.

Extensionseg1Subordinate; set back; lower roof; window & door aligned and well proportioned.

Extensionseg2too big; inappropriate roof; poorly relating windows.

Extensionseg3 Two storey flat roofed extensions will normally be inappropriate.



Extensions at the side of detached and semi-detached houses on the same building line can produce a ‘terracing’ effect which can be overcome by setting back the first floor element.

Rear Extensions


Care should be taken with rear extensions, not only with their design but also with their relationship to neighbours.

Roof Extensions


Roof extensions and dormer windows can easily spoil the balance and proportions of a house when not well designed.

If you live in a house which is a Listed Building or in a Conservation Area you should seek advice from us before you prepare any designs as these properties require very careful consideration.

Similarly if your house lies in the Green Belt or Landscape Protection Area we will give very careful consideration to the impact of your proposal on the landscape.

Your extension may not need planning permission if it is permitted development but we would still encourage you to adopt the principles of good design. Your extension may need Building Regulations approval and you should seek further guidance from Building Control officers on this matter.