The Department's publication "Your Home and Planning Permission (2.76 mb)" gives guidance for householders on what types of development, associated with a house, require or do not require planning permission.

A substantial proportion of planning applications relate to proposed extensions to houses and are considered by the Department under the simplified householder application system. These developments, whilst small in scale, can have a major impact on the street scene and affect the amenities of neighbouring householders. Extensions which are badly designed, or are incompatible with their surroundings, can lead to an undesirable change in the character of an area.

The Department will seek to promote an improved standard of design, for these developments, and protect the amenities of adjacent properties.

Applications for house extensions raise detailed, site specific, issues and each case will be assessed on its individual merits. However, those developments which fulfil the criteria, set out below, will normally be granted. Exceptionally, the criteria may be relaxed, where the extension is required m order to provide basic amenities or  to meet the special needs of a disabled person.

Design

The scale and form of the extension are the paramount design considerations. All house extensions should be subordinate in size to the existing house and should generally match the proportions, roof pitch, shape, and materials of the house. Proposals will also be assessed in terms of their impact on the character and appearance of the surrounding area.

Single-storey extensions, to the rear of a semi-detached or terraced dwelling, will generally be acceptable, where the depth does not exceed 3 metres from the back wall of the original dwelling house, at the boundary with an adjoining dwelling. Where overshadowing may be caused, the height of the extension should be kept to a maximum of 3 metres with a flat roof and 4 metres with a pitched roof If two adjoining houses are to be extended a shared pitched roof may be acceptable. Similarly, where the adjoining property has been extended along a party boundary, an extension of the same depth will normally be acceptable, provided this does not adversely affect other properties.

Dormer extensions should always appear as subordinate elements of the roof and their height and length should be kept to a minimum. Those which would have an over dominant, "top heavy" appearance or would create an obtrusive feature m the street scene will not normally be permitted.

Windows serving main rooms, such as kitchens, living rooms and bedrooms, should be sited so that they do not directly look into similar windows of adjacent dwellings or their private gardens.

Overshadowing

House extensions should not overshadow neighbouring properties to an unreasonable degree. In determining planning applications, account will be taken of the orientation and position of neighbour's windows in relation to the extension. Where an extension would be likely to significantly reduce the amount of light entering the sole or main window of a main room, such as a living room, bedroom or kitchen, planning permission will normally be refused. Exceptions may be made for extensions to older properties, with small plot areas, where some loss of light and privacy may be a
necessary outcome of making essential improvements to substandard accommodation.

Amenity and Parking Space

A reasonably sized private garden area should be retained for usual domestic needs, such as sitting out, hanging out washing, bin storage etc. Proposals may be refused, on grounds of over development, if the remaining garden area is reduced to less than 10 metres in depth. The exceptions would be similar to those described in the "overshadowing" section above.

Space to park cars, within the curtilage of a dwelling, usually improves the environmental and highway conditions of the surrounding area. House extensions which prevent the parking of two private cars within the curtilage of the dwelling, or result in the loss of an only space, or which necessitate the use of an entire front garden for this purpose, will not normally be acceptable. Exceptions may apply to apartments or town houses.

Miscellaneous Householder Developments

In cases where developments, such as garages, outbuildings and other garden developments (including garden sheds, animal accommodation and conservatories), require planning permission, proposals will be considered on their merits, having regard to their impact on the amenities of adjoining residents and the visual qualities and character of the area.

Rural House Extensions

Houses in Green Belts and Countryside Policy Areas normally have the same permitted development rights as elsewhere and there are no objections in principle to house extensions in these areas, or m any other part of the open countryside, subject to the criteria above. However, the impact of extensions on the visual amenities of the Green Belt or CPA will be taken into account.

Large-scale extensions will not normally be acceptable in Green Belts and CPAs. However, where it is proposed to bring an unimproved small dwelling up to modern amenity standards, or to provide additional accommodation for elderly or dependent relatives, a more substantial extension may be justified on grounds of the particular need.
Account will be taken of the degree to which an existing property may have previously been extended and the cumulative impact of permitting a further extension.

Permission will not normally be granted where the extension requires the use of land outside the established curtilage of the building. Exceptionally, permission may be granted on the grounds of need or road safety, where for example the existing access is substandard.

Accommodation for Dependent Relatives

House extensions, to provide partially self-contained accommodation for elderly or dependent relatives, may be an acceptable alternative to a separate house in the countryside, and particularly in Green Belts and CPAs.

All additional accommodation should normally be attached to the existing property and be internally linked, although another separate access is acceptable, to enable the accommodation to be partially self-contained.

The construction of a separate building, as self-contained accommodation, within the curtilage of an existing dwelling house, will not be acceptable, unless a separate dwelling would be granted permission in its own right. Where an extension to the existing house is not practicable and it is proposed to convert and extend an outbuilding, planning permission will normally depend on whether the development provides a modest scale of accommodation, to ensure the long term use of the building as part of the main dwelling.

In all cases, careful consideration will be given to the impact of proposals on neighbouring dwellings and any permissions granted will be subject to a condition that the extension should only be used for ancillary residential purposes in connection with the main dwelling, and not as a separate unit of accommodation.