Design and Development Control Guidelines
2 EXTENSIONS TO HOUSES
2.1.1 Extensions to houses can be a useful way of extending the range of housing and help to provide a better mix of accommodation. However their construction, if not thoughtfully carried out, can lead to problems for adjoining householders and can contribute to a general decline in environmental standards.
2.1.2 The guidance is divided into two sections. The first section sets out the basic design principles. This is followed by detailed design guidance on a range of extensions most commonly proposed in the borough. It is not possible to anticipate and give guidance for every type of extension. When a particular application is not covered by the guidance, the basic design principles will still apply.
2.2.1 The basic principles of all new extensions are outlined in Policy H9 of the plan. In general extensions should be subordinate to the existing building. In addition:
- the siting, design and external appearance should respect the character of the existing building and adjacent building;
- the development should not adversely affect the privacy and amenity of adjoining properties including daylight, sunlight and outlook; and
- the development should not result in over-development in terms of scale and mass, car parking and remaining amenity area.
2.2.2 In determining the impact of any proposal the Council will take into account:
- the need to protect the privacy and amenities of adjoining house owners;
- the need to protect daylight and sunlight available to neighbouring properties and to the future occupiers of the development;
- massing and proximity to the property boundary and adjoining buildings and other siting considerations;
- the overall form, shape and proportions of the extension;
- the roof type, layout of doors, design and style of windows;
- the external materials and appearance;
- vehicle parking arrangements; and
- A proposed extension should not result in adverse effect on the privacy of adjoining householders.
- Where loss of privacy and/or overlooking may be a problem side windows which overlook an adjoining property should have high-level or obscure glazed windows. A high-level window is one with a sill height of at least 1.7 metres above floor level.
- An extension which proposes a flat roof for use as a balcony will normally be unacceptable on privacy grounds.
2.2.4 Sunlight and daylight:
Extensions should be designed to avoid unacceptable loss of sunlight, ventilation and daylight to adjoining houses (or the building being extended). The dimensions for extensions for different types of dwellings set out later in this section have been chosen with this issue particularly in mind.
2.2.5 Siting considerations:
- The Council will take into account the extent to which any extension is visible by the public and its effect on the street scene.
- Side extensions to corner houses or properties on prominent sites should have pitched roofs of a type to match the existing dwelling. Sight lines should not be obstructed.
The design of extensions should recognise the principle that the extension should be an additional volume subordinate to the existing building. An extension should not make a dwelling less compliant with Part M of the Building Regulations.
2.2.7 Doors, windows and guttering:
- The doors and windows of the extension should generally repeat the proportions, design, alignment and materials of the openings in the original dwelling.
- Guttering on all extensions should be fixed in such a manner that it does not over-hang the boundary.
- It is usually preferable for walls on or very close to the property boundary line not to have windows in them and, in any case, windows, where provided, should be fitted so that they cannot open over the boundary line.
- The height of any extension should not exceed the ridge height of the existing building.
- The roof lines of the extension should generally be parallel to those of the existing building and eaves lines should generally follow through.
- The roofs of new extensions should follow the pattern of the main roof and have the same angle of pitch.
2.2.9 Materials and appearance:
- The external materials of the extension should be in harmony with the materials of the existing building and character of the area.
- The design of the extension should respect the style of the existing building.
2.2.10 Vehicle parking and garages:
- In accordance with UDP Policy T17, the Council will normally oppose the loss of on-site parking provision where this would be likely to cause additional on-street parking to the detriment of amenity or traffic flow.
- Where a parking space is proposed to meet parking standards, it should wherever possible be sited behind the front main wall of the dwelling in order to protect residential amenity and the appearance of the street.
- Where a garage is proposed to meet parking requirements, it should be sited so as to allow a minimum of 5.7 metres from the back edge of footpath to the garage door, with the exception of garages in rear gardens served by a rear accessway.
- Detached garages in rear gardens or at the rear of any premises served by a rear access should be so sited that the doors do not open over the boundary of the site.
- Where access is to be obtained to a garage or parking space, other than directly from the public highway, the occupiers of the premises should enjoy the right of access and the access-way should be adequate. The parking space or garage should additionally be positioned to permit vehicles to satisfactorily turn onto and off the access-way.
2.2.11 Refuse and storage areas:
A bin enclosure to accommodate at least one dustbin per dwelling should be provided in a convenient location for collection. The provisions of BS5906:1980 and of Part H4 of the Building Regulations should be followed, as regards siting and carrying distances.
2.2.12 Garden size:
Usable gardens are particularly important for family houses. Proposals should ensure that adequate garden and amenity space are maintained.
Proposed extensions should avoid the need to remove such features as healthy trees and established shrubbery. Where proposals involve the felling or lopping of existing trees and hedges, suitable new planting will be required.
2.3 Detailed design guidance
2.3.1 Roof extensions:
- Loft and roof space extensions should not normally exceed the ridge height of the existing building, or by reason of design or massing be detrimental to the form of the existing roof.
- Roof extensions should, if possible, have dormer windows facing to the rear; dormers on the hipped side of a pitched roof should in general be avoided.
- All roof extensions should be set back from the main wall of the dwelling on which they are proposed to avoid creating the appearance of an extra storey.
2.3.2 Rear extensions:
- On semi-detached and terraced houses, single storey extensions at the rear and on the boundary with the adjoining half of the property should not normally exceed 3.1 metres in height (to eaves level with pitched roofs) above existing ground level or 3.5 metres in depth from the rear of the property. Pitched roofs are preferable to flat roofs on single storey rear extensions provided that they do not affect neighbours' amenities unacceptably.
- Two storey extensions should normally be avoided on terraced houses in view of adverse effects on adjoining properties. Where it is considered that there will be no adverse effects, two storey rear extensions may be acceptable on semi-detached houses but should be set in 2 metres from the common boundary with the attached property at first floor level. Exceptions to this guideline may be made in certain cases as follows:
- where the property as originally constructed had a rear projecting nib on the boundary, the ridge of which exceeds the height of the first floor windows of the adjoining property; or
- certain houses built on the Stevens Estate in Welling classified as small Stevens houses and characterised by a single 6-pane round-bay window to each floor of the front elevation.
- On converted dwellings or new build flatted developments, applications for ground floor rear extensions that are likely to affect the amenities of other flat occupiers will be resisted.
2.3.3 Side extensions:
- Single storey proposals to extend at the side of a property up to the site boundary and within the depth of the property will normally be acceptable providing that the design matches the existing house. With plots that have at least 4 metres between the flank wall of the dwelling and the site boundary, the extension should be set at least 1 metre from the boundary.
- Two storey side or first floor extensions over existing accommodation should be designed to be subordinate to the main dwelling. Ideally this should incorporate a set-back of the front elevation of the extension. The roof plane of the extension should respect the roof plane of the original house, thereby lowering the ridge line.
- New two storey side extensions on plots with at least 4m between the flank wall of the dwelling and the site boundary should be set in at least 1m from the boundary.
2.3.4 Chalet extensions:
- All extensions should complement and enhance the character and appearance of the street scene. Extensions should respect adjoining properties and pay particular regard to the integrity of design and 'balance' of the chalet pair. Extensions, which are over-dominant or detract from the original style or features of the chalet, should be avoided.
- Extensions should be set back from the main front wall of the dwelling (except where this would conflict with guideline (1). Hipped roof extensions should be set back a minimum of 0.5 metres and flat roof 'box' extensions by 2 metres.
- First floor side extensions should normally be limited to a maximum overhang of 300 millimetres.
- Single storey rear extensions between the common boundary and the kitchen nib should not extend beyond the depth of the original kitchen nib.
2.3.5 Front extensions:
- The design of porches and hall extensions should respect the style, character and massing of the existing building and should relate to the general street scene. Porches should not normally exceed 1.1m in overall depth and 2m in overall width.
- Front extensions of a greater depth than a porch should normally be avoided. However, in certain special circumstances front extensions may be acceptable e.g. detached houses on large plots with substantial space around the dwelling and for houses in streets with irregular building lines. These should only be considered where the extension results in a positive townscape improvement and it respects the style and character of the original dwelling.
- Front extensions will normally be resisted where they would encroach upon a vehicle hardstanding to the extent that a car parked on the hardstanding would be likely to overhang the public footway.
2.3.6. Detached Houses:
- On large plots with substantial space around the dwelling, specific guidelines are not applicable but any proposal should conform with the principles outlined in this guidance.
- On smaller plots with small houses built to estate standards, proposals to extend need careful consideration to maintain the integrity and character of the original layout and design.
Proposals to extend bungalows should pay regard to the principles outlined in this guidance. Proposals which are likely to adversely affect the character and appearance of the dwelling will be resisted.
2.4. Conservation Areas and Listed Buildings
2.4.1 Extensions can have a detrimental effect on the character of a building and cumulatively on the character of a whole area. Listed Buildings are particularly sensitive and any alterations or extensions will require special consideration. Extensions to the principal façades, including roofs, will not normally be acceptable.
2.4.2 Although no general requirements can be laid down for development within Conservation Areas, the specific dimensions of proposals will be looked at carefully to ensure they fit in with the character of the Conservation Area in which they fall.