General design principles when extending your home




To match or not to match?design principles

Most of the time under the present system of town planning council’s have generally preferred extensions that follow the original building in terms of materials, roof design, windows etc. More recently there has been a movement towards extensions that display their own character, a lot of these have been largely glass and so the appearance does not perhaps overwhelm the existing although in some cases rather more contrasting materials have been used. However under the current permitted development rules for most extensions it will be necessary to match the existing materials in order to avoid the need for town planning consent.

side extension
The first floor is set back from the front wall, the lower roof is in part needed as the extension comes off a lower landing on the stairs and the original brick wall rendered over to give a uniform appearance.
Some views are that an extension should be able to be recognised as an extension rather than incorporating it too much into the existing building (although less often by householders themselves). It is often preferred for an extension to be seen as a less dominant part of the building, in other words with a typical two storey extension it may be preferred to set it back from the existing front wall and have a lower roof rather than keeping it level with the existing front and constructing a larger roof over the extension and existing part.
Staggering the structure can also make slight differences between the new and existing materials less noticeable than trying to match them on a flat surface.
With regards to matching materials, it can be difficult to obtain bricks of a similar type, the existing bricks will inevitably have weathered and older buildings are often constructed from bricks that are no longer available. In the past most bricks were sourced from local manufacturers, most of them, except a few producing high quality hand made bricks have gone and the majority of bricks today are now supplied by just a few major companies. Modern bricks are often a different size from older ones. It may be possible to obtain some matching bricks from reclamation yards but these will generally be more expensive than new mass produced bricks and it is obviously necessary to make sure sufficient are available as it may not be possible to obtain any more (there may also be a greater wastage with reclaimed bricks with damaged or otherwise unusable ones mixed in).
A contrast of materials such as tile hanging or rendering to the new part can sometimes give satisfactory results or alternatively the existing building can also be clad to give a more consistent appearance. This can be particularly useful if the existing building is finished in unattractive materials or in a poor state or repair and may be away of upgrading the insulation to the buildings as well.
2 storey side extension tile hung
Although this extension uses different materials they work quite well together.

Boundary spacing

Planning authorities generally have their own guidance with regards to spacing off the boundary and this may vary according to the location, what may be acceptable in what is already a dense urban environment may not be acceptable in a very spacious neighbourhood. In general a building should be completely on its own land which includes gutters, eaves etc. The Party Wall Act does allow some un-reinforced foundations to encroach the boundary but this does not generally apply to other parts of the building. It will therefore often be necessary to be at least 2-300mm from the boundary unless specifically agreed with the neighbour, in some situations, particularly upper storeys to houses 1m may be preferred which also provides a gap for maintenance. In some instances such as areas where there is a more spacious layout or the proximity of buildings on adjacent sites may make greater distances preferred.
Although extensions at the rear are usually less troublesome in this respect, where gardens are reasonably short it may be that it is considered that too little ‘amenity space’ is left. A figure of about 11m garden length is sometimes quoted but in many areas original gardens may be less than this, the permitted development town planning rules require at least 7m beyond a multiple storey extension at the rear.(see Town Planning Section) The problem may be compounded where properties backing on at the rear are also close to the boundaries giving restricted spacing between them, this may particularly be difficult with new upper storeys that might create a greater degree of overlooking into other properties such as where they are primarily bungalows. High fences, walls or hedges can to some extent mitigate the effects at ground floor level.
At one time the front building line of a property was fairly sacrosanct, although generally it is not a common way to extend there may be situations where it is acceptable particularly if there is no a rigid pattern of development. There may still be a minimum requirement as to the spacing from the front. Where there are parking spaces to the front of a building (and this may also apply to side extensions such as garages) it may necessary to ensure adequate off road parking is maintained. Where
the access is onto a main road or near a junction, it may also be necessary to provide on site turning so that cars can always enter and leave the highway in a forward gear.

front extension
Front extension which does not rigidly follow the style of the main house but makes an attractive feature.
The building regulations can also restrict the proximity to boundaries, particularly where there are windows or combustible materials (such as timber) on the external face (this is primarily concerned with the spread of fire from one building to another). At less than 1 metre to the boundary the maximum size of windows is 1m² and there must be at least 4m between them. The amount then increases the further away the building is from the boundary such that at 6m the area of windows or combustible material is unrestricted under these regulations, although other criteria such as insulation may limit it. Where the boundary is next to a road etc. the measurement can be taken from the building to the centre of the road.

Effects on neighbours

Extensions should not take an excessive amount of light from neighbouring properties. Town planners will take account of this aspect but to some extent it is also governed by rights to light, where a property has benefited from this for twenty years or more reasonable provision must be maintained. What may be considered acceptable may vary according to other windows that may be in the room and its use.
With extensions to the front or rear the new building may not be encroaching any closer to the neighbouring windows but could nonetheless either shadow the adjoining house or garden or at least be excessively imposing on them. From the point of view of sunlight it may be less critical if the extension is to the north of the neighbours but may still be considered unsatisfactory on other grounds. With extensions relatively close to the boundary sometimes a theoretical line is drawn from neighbouring windows at an angle of 45degrees which should generally not be encroached by the extension. This may not be rigidly enforced in relation to small single storey extensions.
New windows to extensions or sometimes new windows to the original building made necessary by the new layout can cause overlooking. This is usually more critical to the sides where there may be more limited spacing although there are some restrictions within the town planning permitted development rules in this respect.
 It is less likely to be critical at the front and rear unless the gardens are unduly short, in this respect there is generally inherently less privacy at the front of a property and so this is less likely to be a problem. The garden immediately behind a property is often considered a more private amenity space and so overlooking this would be more critical than towards the end of a long garden.
Overlooking at ground floor level can often be reduced by fences, hedges etc. of a suitable height. Overlooking from windows to bathrooms is generally less of a problem, in the main these would be obscure glass and possibly not have any low openings. Windows to habitable type rooms (bedroom, living rooms etc.) can be more difficult particularly at upper floors, some authorities are not keen on over reliance of obscure glass as it is rather too easy to change in the future. High level windows (minimum height generally in the region of 1.7m) may be acceptable in this respect but could conflict with requirements for secondary means of escape under the building regulations for first floor rooms if this is the only window to the room.
Balconies, first floor conservatories etc. can be contentious where they might allow easier overlooking particularly from a ‘day use’ area. This can sometimes be overcome by high level obscured balustrading or walling to critical positions, although in some situations this may defeat the purpose of it where it might obscure a particular view.
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