Extensions to houses
This advice note provides guidance on the design of extensions to houses. Most householders considering an extension know what size of extension they want, where they would like it to go and what they want it to look like. It explains the planning considerations that need to be taken into account in order to achieve an acceptable design to put forward for planning permission.
September 2012 Is planning permission required?
If you wish to extend or alter your Some housing developments built house you may require planning more recently, especially since the permission. Houses (not flats) benefit 1960s, may also have the usual from ‘permitted development permitted development rights rights’ which allow for some small removed as a condition of the extensions to be constructed original planning permission, without the need for planning especially if they had an unusual permission. This guide is for or specific design. If this is the extensions where planning case it will mean that even minor permission is likely to be required, extensions will require planning however the general principles can permission. also apply to smaller extensions that do not require planning permission. If permitted development rights are withdrawn this will be stated on the For further information on whether original planning permission for the planning permission is required property. Any permissions dating please refer to the planning portal from 1999 onwards are available to at www.planningportal.com view via the Planning Public Access There are special requirements for system on the council's website properties in conservation areas (www.norwich.gov.uk). If you do in terms of the type and size of not hold a copy of a permission the extension, particularly in areas granted between the early 1960s covered by article 4 directions. and 1999 and wish to inspect a Article 4 directions are used locally copy, you can do so in person at to reduce the extent of permitted the planning reception in City Hall, development rights where such St Peters Street, Norwich, NR2 1NH development is considered to or, if you are able to confirm the harm the character of the area planning application reference (eg front extensions in a row of number, we will be able to provide historic terraces). an electronic copy of the decision on receipt of a request to Currently, three conservation areas [email protected] in Norwich are partly covered by article 4 directions. These are the city centre, Bracondale and Heigham Grove. For more information on these areas please refer to www.norwich.gov.uk/ article4directions.
2 | Extensions to houses – advice note Other types of permission How will a planning that may be required application be assessed?
If your house is listed grade I, II* or II, The following considerations from you will also require listed building Local Plan policies will be taken into consent for alterations inside and account when the council determines outside the house. an application for an extension or alteration to a dwelling: Within conservation areas six weeks’ notice needs to be given to the tree • How the extension relates to protection officer of any works to the existing appearance of the trees in order to consider whether house and the character of the the tree should have a Tree surrounding neighbourhood in Preservation Order (TPO). It is also terms of scale, size, shape, important to check whether a tree materials and design details. already has a TPO. • Neighbour impact in terms Before you submit your planning of possible overlooking, application, it is also important to overshadowing or being make sure that proposals will meet the overbearing. requirements of building regulations so any permission gained does not • The change in the footprint of subsequently have to be altered to the house and/or building height meet changing requirements. and whether this will result in a cramped form of development in relation to the site. • Taking into account existing building lines and visual continuity.
Other considerations
The extension may need to be designed around existing trees if they merit preservation. In some It is important to consider other cases a tree may be removed if requirements such as whether a another tree or trees are planted building is listed grade I, II* or II, elsewhere within the garden area whether the house is in a conservation to compensate for the loss. area and whether any trees are Extensions should also consider protected. including bin and cycling storage areas and if these are not already provided elsewhere in the house or its grounds. This will be particularly applicable if an extension will result in the loss of existing garage or storage provision.
Extensions to houses – advice note | 3 If an extension is being proposed for and privacy in rear gardens will ancillary use to the house, for example differ depending on where you may as annex accommodation, other live in the city. In outer suburban considerations will be taken into areas it will generally be desirable to account with regard to the maintain greater distances between appropriateness of the extension properties, for example a minimum and further advice should be of 20m. In Victorian inner suburbs sought. Anyone considering and the city centre this distance may building an extension, whether it be much less depending on the requires planning permission or not, existing character of development is advised to inform their neighbours in the immediate neighbourhood. of their plans, particularly in relation to the likely timing of building works. Front extensions and porches Right to neighbour privacy The front of a house is usually the It is important to consider the impact part of the house most visible in the of any extension on neighbouring street and so the part of the house residents and their right to privacy, given most attention in terms of particularly with regard to garden making a house look attractive. and patio areas to the rear and In most cases large scale front sides of a property. extensions are unlikely to be Design considerations to prevent considered acceptable as they direct overlooking include: usually result in significant change to the original appearance of a • the configuration of internal house. However, in some instances, accommodation – where the for example detached houses with different rooms are located unique designs, the whole house within the house may be able to be remodelled. It is • where window openings are therefore recommended that any positioned, for example avoiding large scale extensions to the front of windows in side elevations, a house are designed with sufficient particularly upper floors architectural expertise in order that • the use of high level windows at the appearance of a house is ground floor height with internal enhanced rather than spoilt. sill height of at least 1.6 metres Small scale front extensions, such that allow light in but prevent as porches, are more likely to be direct overlooking considered acceptable as they • the use of obscure glass and have much less impact on the restricted opening mechanisms appearance of a house and can • high walls or fences between contribute to improving energy opposing ground floor windows. efficiency. It is important to note whether similar porches have It is important that sufficient already been constructed on distance is maintained between neighbouring houses, as this is more the back of houses. Norwich has likely to result in an application a varied character and density of being considered acceptable, housing and expectations of space particularly for terraced houses.
4 | Extensions to houses – advice note ✔✘✘
Acceptable porch extension to a terrace house ‘fit in’ with the existing appearance of the house.
Side and rear extensions
The majority of extensions are to permitted, but this will need a the side and rear of houses. These carefully considered design should be designed to respect the approach by a suitably qualified scale, size and shape of the original professional designer. building. They should not dominate over the original house; materials Side extensions should take into should match as closely as possible; account the existing spacing between and detailing should match the houses in the street – preserving gaps existing design – for example, new where they are an important part of and existing windows should line a street’s character to avoid cramped through with each other horizontally development and the creation of and vertically and proportions a ‘terracing’ affect, where gaps should be respected. In some cases between houses are removed. It is where an extension is seeking to usual for a larger space between introduce an innovative design, for houses at first floor than at ground example passivhaus, contrasting floor, so ground floor side extensions design and materials may be may, in some circumstances, be considered acceptable.
Extensions to houses – advice note | 5 ✔✘ Acceptable side extensions in streets of similarly designed semi-detached houses in the outer suburbs.
In areas where large detached Terrace houses were often built with houses are set within spacious existing rear projections and these grounds, side and rear extensions may have been extended over time. should reflect the architectural It is important that a reasonable gap characteristics of the original is retained between the houses to building. In streets where buildings ensure adequate levels of light are are spaced out, and buildings are maintained and to avoid a ‘tunnelling’ placed in regular plots, single storey effect. Single storey extensions side and rear extensions may be with tiled lean-to roofs can result in considered acceptable depending significant loss of light and appear on space (for example 1930’s semi overbearing in some circumstances. detached houses.) In areas where A more acceptable approach housing is very close together, it is likely would be to design an extension that only single storey rear extensions with a glazed roof which has a will be considered acceptable. relatively shallow pitch.
✔ ✘ Rear side extensions to terraces should be careful not to result in the loss of light and overbearing form to neighbouring properties.
6 | Extensions to houses – advice note Achieving architectural In asymmetrical houses it may be considered more appropriate to balance in side have a seamless extension with a extensions continuous building and eaves line. In these cases it is very important to The scale and proportions of a side have continuity in both materials extension need to be designed and design detail to match the carefully so they do not disrupt the existing house. The width of the architectural balance of a building. extension and design features, such The architectural balance is the as windows, should match up in way in which the various parts of terms of scale, size, shape and a building are seen together and proportions with the architectural how this unifies the appearance of elements of the house. a building and contributes to the attractiveness of a house. The approach will differ between a building that is designed to be symmetrical and one designed to be asymmetrical. Where a house already has a symmetrical frontage the usual design approach is to set the extension back from the original building line, ensuring the width of the extension is no more than half the width of the house, and also lowering the eaves line. This will ensure the extension will be architecturally subservient and will not disrupt the existing symmetry of the design. ✔ A seamless side extension to an asymmetrical house.
Alterations to roofs
Roofs are a very visible part of a house and therefore careful consideration needs to be given to how an extension relates to the rest of the house and how it is viewed within the street. Important ✔ considerations include: • installing roof lights which are Side extension to a symmetrical straightforward to fit, are flush ‘double fronted’ house. fitting and will result in less change to the appearance of a roof
Extensions to houses – advice note | 7 • the degree of slope of the roof are visible they should be set away pitch. Dormer windows are from roof hips, verges, ridge and more likely to be considered eaves, as well as other roof features. acceptable within roof pitches over 40 degrees and unlikely to be acceptable in roof pitches below 30 degrees as they will appear too dominant • where dormer windows are permitted on front roof slopes or other prominent roof-slopes, ensuring these reflect the design of the original building. In most cases this will be a traditional pitched roof or catslide style dormer • being aware that large scale ✔✔✘ dormers required for headroom are likely to only be acceptable Acceptable designs of roof lights on rear roof slopes or less and dormer windows. prominent roof slopes unless already a feature of existing Innovative designs houses in the street • protecting the privacy of The aim of this guidance is not to be neighbouring houses from being prescriptive but to explain common overlooked approaches to determining house extensions. In some cases an • ensuring the form and detailing opportunity exists to create a more of a dormer relates to existing unusual and unique innovative design, design features of the house, for especially if the existing house already example in design detail and has a unique or unusual design. Such materials design will need to be considered • making sure dormers reinforce carefully and it is recommended symmetry and architectural that the householder employs a balance, for example placing suitably qualified architect. it in the same vertical line as windows below. Note: Large ‘box’ style dormers are Further advice a modern way of maximising internal This advice note only offers accommodation in roof spaces. The guidance on designing extensions. modern box form does not sit well on Further information will need to be obtained if the development is more traditional roof pitches and considered to have an impact on they can dominate over the original trees (especially in a conservation house and be overbearing over area). For seperate Building neighbouring houses. ‘Box’ style Regulations approval please dormers are unlikely to be considered contact CNC Building Control acceptable on front or other on 01603 430100. prominent roof slopes, and if they
8 | Extensions to houses – advice note