Roof Extension

1. Roof Extensions

The roof of a building is an important element of its design. Unsympathetic extensions can have a dramatic effect upon the visual appearance of a building and its setting. If the property is a listed building or within a conservation area special care is needed when altering the roof.

2. What are the common forms of roof extensions?

  • Front roof slope - Roof extensions located on front roof slopes facing roads always require planning permission. New roof extensions on highly visible and unaltered roof planes will generally be resisted. Front roof extensions may be acceptable where front roof planes have already been altered sensitively, or where the rhythm of the existing roof planes is less regular.
  • Rear roof slope - visible in public realm - The degree of visibility of the rear roof slope varies considerably; Rear roof extensions which are not highly visible from public areas will be assessed on the basis of their impact on the house and its immediate surroundings.
  • Rear roof slope - only visible from other gardens - Rear roof slopes which are only visible from surrounding gardens still matter, since these have an impact on the amenity of the neighbouring houses. It is just as important for such roof extensions to relate well to the proportions, roof forms and massing of the existing house and its neighbours as elsewhere.

3. What are the benefits of roof overhangs?

Roof overhangs can add to the value and usefulness of a building in several ways:


Extending the roof breaks up the 'boxy' look of rectangular buildings. Canopies and extensions also help a pre-engineered building blend in better with neighboring structures in residential or upscale commercial areas.

  • Shade and Shelter - When located over a doorway, even a one-foot overhang offers you some shelter from the rain and shade from the hot summer sun when you are working near the entrance or just unlocking the door to go in.
  • Runoff - For buildings with no gutters, overhangs help control runoff by preventing rain and melting ice and snow from splashing against the walls and directly in front of the doorways.

4. What are the permissions required to re-roof a house?

You do not normally need to apply for planning permission to re-roof your house or insert roof lights or skylights unless your building is listed. But check with the council before finding an extension builder if you are changing the tile type or colour. You will have to apply if: You want to build an addition or extension to any roof slope which faces a highway.

  1. The roof extension would add more than 40 cubic metres to the volume of a terraced house or more than 50 cubic meters to the volume of any other house (these volumes count against the volumes for any other extensions)
  2. The work would increase the height of the roof

5. What are the design guidelines?

To extend the roof of a building that forms part of a pair or terrace of buildings, then following guidelines.

  1. New roof slopes should not be steeper than an angle of 70 degrees to the horizontal plane
  2. New windows in a roof slope should preferably continue the spacing, frequency and type of windows in the storeys beneath, continuing the same visual balance between vertical and horizontal elements
  3. Roof materials should match the original in substance and pattern
  4. Important original features (e.g. gables and turrets) should be retained intact and accommodated satisfactorily in the extension design
  5. Roof extensions to properties with sloping roofs should generally retain the use of sloping roofs
  6. Party walls should not exceed 250 mm above finished roof level unless a greater height is required under the Building Regulations as a result of the height of an adjacent roof extension
  7. Any extension should not exceed the height of the lowest point of the roof on the main part of the building