PPS 7 (Addendum): Residential Extensions and Alterations
Annex A: Context and Design: Roof Extensions
A14 An extension or alteration which copies the roof type and angle of pitch of the original residential property will be more successful than those proposals that introduce a completely different type of roof. The roofing material of any pitched roof extension should seek to match that of the original. Flat or mansard roofed extensions to traditional buildings are seldom harmonious. However, they may be acceptable where they are not open to public views.
A15 The use of loft space to provide bedrooms or other living space can often provide additional accommodation. However, alterations to the roof profile of any building can be particularly sensitive as roofs play an important part in contributing to a building’s appearance and the overall character of the area. An extension to the rear of a property should ensure that the roof of the extension does not project above the ridge of the existing dwelling as this can give an unsightly view along the streetscape. Rooflights, which lie parallel with the plane of the roof, are a particularly sympathetic way of providing light to a room within a roofspace. They may often constitute permitted development but care should be taken to ensure compliance with Building Regulations where such windows are intended to provide a means of escape.
A16 The regular repeated rhythm and uniformity of roof forms and chimneys may be a particular feature of a group of similar buildings or the wider townscape and should therefore be retained. If elements, which are not part of the original property are proposed, for example, a dormer roof extension, these should be designed in a manner that complements the period and style of the original property, or to reflect the best examples of such features on properties of a similar period in the area.
A17 Where a dormer is open to public view, it can interfere with both the original design of the existing building and cause a visual intrusion into the street scene or rural setting. Dormer windows to the front or side of a property will be resisted in areas where they are uncharacteristic, particularly large box dormers that are over-dominant often extending the full width of the roof. The size and number of dormers should therefore be kept to a minimum to avoid dominating the appearance of the roof and should be located below the ridge line of the existing roof. Positioning dormer windows vertically in line with the windows below and ensuring that they are smaller in size will usually avoid a top-heavy or unbalanced appearance.