Goal: To achieve extensions to dwellings that respond to the needs of the occupants in a way that is sensitive to the character and appearance of the original dwelling and street scene.
p83.
Extensions to dwellings can have a significant impact on the character and appearance of a dwelling itself and the street or area in which it is set in. A well-designed extension can enhance the appearance and value of a property, whereas an unsympathetic extension can have a harmful impact, create problems for neighbouring residents, and affect the overall character of the area. To establish the effect a proposed building will have on existing properties with regards to obstructing daylight to existing windows/rooms, check the 25 and 45 degree rule.
p84.
Extensions present an opportunity to improve insulation and heating systems in a property or incorporate water saving devices. This can increase the sustainability of a home and lower its carbon footprint whilst reducing the cost of heating a home. Consider carefully how your proposed extension could improve the thermal efficiency of your property. Some smaller-scale extensions may constitute ‘permitted development’ which means they do not need planning permission.
To understand if your extension may be permitted development see:
p85.
If planning permission is not required, we would still strongly encourage you to follow the best practice guidance in this document to ensure that the design of your extension can be the best that it can be.
To make your home or extension more sustainable see:
p86.
If a building has been identified as being Statutorily Listed or is located within a Conservation Area or AONB, some forms of development or alteration that would otherwise be classed as permitted development will require planning permission, Listed Building consent or combinations of these.
p87.
A Design and Access Statement may need to be submitted for applications for Listed Building consent and for planning applications in Conservation Areas.
p88.
Extensions to historic buildings can be harmful if their significance is not fully understood.
p89.
The Council can provide further assistance and guidance about what does and does not require planning permission and advice about the design of the proposal. If planning permission is required, the Council has a validation checklist for householders to help people in preparing applications and ensure all necessary information is included, for more information see:
Calculate the volume of the development. Certain development volumes will fall under permitted development, you can find out more information on what are permitted development volume limits here:
Extension in keeping with the existing character and appearance of the house (Kingston Blount) Successful two-storey extension subordinate to the principle dwelling Successful contemporary extensions to a traditional building in Watlington Another example of an extension in keeping with character and appearance of the original dwelling
Design principles - Householder extensions
Ensure the scheme:
responds to and respect the character and appearance of the area and street scene;
maintains established building lines and predominant plot patterns;
uses simple, uncomplicated building forms that complement and coordinate with the scale, form and massing of the original dwelling;
uses building materials matching those of the existing dwelling (or justification has been provided explaining the appropriateness of the alternatives proposed);
ensures the original building remains the visually dominant element of the property (whether it is an extension, a self-contained annex, an outbuilding or a garage);
has a roof form appropriate to the original dwelling, generally this should be constructed with the same angle of pitch as the existing roof. Overly complicated roof profiles to be avoided;
ensures any existing external access from the front to the rear garden has been retained where possible;
responds to the existing rhythm of windows, door and openings. Note that the position, size, proportion, height and style of new windows and doors and the ratio of solid wall to openings all help to define the character of a dwelling;
demonstrates that it will not result in the significant loss of light (as determined by BRE calculations where deemed necessary).
Neighbouring amenity:
Developers and applicants should be mindful of the impact of their proposals on the amenity of future and existing adjacent occupiers. Proposals should not give rise to any unacceptable harm.
Extensions and alterations must:
have been informed by the positioning of neighbouring dwellings and an understanding of the potential impact development could have upon them;
demonstrate that it will not result in inappropriate overshadowing, a loss of privacy or have an oppressive or overbearing impact on neighbouring properties;
provide a minimum of 10m between habitable windows and side elevations;
comply with the 45-degree rule set out within the BRE guidance;
comply with the 25-degree rule set out within the BRE guidance;
Note: All design principles are applicable to all scales of development unless otherwise specified; *minor applications, **major applications
Side extensions
p90.
Side extensions should normally be set back from the front of the house to retain the proportions of the original building and reduce the visual impact between existing and new development. This can be particularly important on symmetrical properties or identical semi-detached properties. The original building should remain the visually dominant element of the property (whether it is an extension, self-contained annex, an outbuilding or a garage).
p91.
Side extensions should avoid development, where extending at two stories or above, up to the site boundary, this results in a ‘terracing effect’, impacting the quality of the street scene and necessary access/maintenance.
p92.
Extension should maintain a gap between the extension and the site boundary or have a lower ridge height than the main building. The extent of the gap should be determined by the pattern of development in the area; however, gaps should be no less than 1 metre wide for the benefit of access and maintenance.
p93.
An alternative way of avoiding a terracing effect is to set the first-floor element of the extension back from the front elevation – it should be set back at least one third of the depth of the dwelling.
p94.
Two storey extensions should generally be constructed with the same angle of pitch as the existing roof, particularly where development is at the same ridgeline
p95.
Single storey side extensions will have a lesser impact on the appearance of a dwelling than two storey extensions. A flat roof may be acceptable for a single storey extension, provided it is carefully designed – e.g. including a parapet wall with a coping stone on top.
Key:
Acceptable in principle
Example of modest single-storey extensions in line with permitted development. Subservient in scale and massing. Best practice is to setback development to preserve the principal dwelling and maintain its character. Development should not be forward of the principal elevation. Materials and detailing should match the principal dwelling.
Potentially acceptable in principle
Example of a one and a half-storey extension. Subservient in scale and massing, setback to preserve the principal dwelling. Modest skylights or dormer windows can be acceptable. Materials and detailing should match the principal dwelling.
Unlikely to be acceptable in principle
Example of a two-storey extension. Roofs must match the existing dwelling, and not exceed the finished ridge and eave height. Flat roofs should be avoided where possible. The proportion and rhythm of window or door openings should be in line with the principal dwelling. Development must not be overbearing in scale or massing compared to the principal dwelling. Infill between buildings must not have a terracing effect.
Figure 43: Side extensions, illustrative examples
Figure 43: Side extensions, illustrative examples
Design principles - side extensions
Ensure the scheme:
is subservient to the principal dwelling;
is significantly set back from the front of the house (at least one third of the depth of the dwelling) and set down from the original roof ridge of the dwelling, or otherwise be justified for not doing so;
retains important gaps within the street scene and avoid creating a continuous building line. To reduce such a ‘terracing effect’, it is desirable to maintain a gap between the extension and the site boundary and for the extension to have a lower ridge height than the main building. The extent of the gap should be determined by the pattern of development in the area but, in general, it should not be less than 1 metre wide. An alternative way of avoiding a terracing effect is to set the first-floor element of the extension back significantly from the front elevation;
is constructed with the same angle of pitch as the existing roof;
includes windows that face the street to provide passive surveillance;
demonstrates that it will not result in overshadowing, a loss of privacy or an oppressive or overbearing impact on neighbouring properties.
Note: All design principles are applicable to all scales of development unless otherwise specified; *minor applications, **major applications
Rear extensions
p96.
Rear extensions should not result in significant overshadowing of a neighbour’s property. Rear extensions which are not visible from the street or public rights of way and do not negatively impact on neighbouring properties can be expressed in many forms, including through the use of contemporary architecture. In addition to the distance between properties, there are a number of solutions or more detailed design measures that can be employed to maintain privacy surrounding the placement and design of buildings. This could include appropriate positioning of windows (staggered or otherwise), arrangement of habitable rooms to reduce direct views; and creating varied floor levels. As a rule, extensions that alter the existing ridge of the roof or significantly alter the roof profile will not be accepted where this detracts from the character and appearance of the original dwelling and / or the street scene.
Key:
Acceptable in principle
Example of modest single-storey extension in line with permitted development. Subservient in scale and massing. Best practice is to setback development to preserve the principal dwelling and maintain its character. Development should not be forward of the principal elevation. Materials and detailing should match the principal dwelling.
Potentially acceptable in principle
Example of a one and a half-storey extension. Subservient in scale and massing, setback to preserve the principal dwelling, modest skylights or dormer windows can be acceptable. Materials and detailing should match the principal dwelling.
Unlikely to be acceptable in principle
Example of a two-storey extension. Roofs must match the existing dwelling, and not exceed the finished ridge and eave height. Flat roofs should be avoided where possible. The proportion and rhythm of window or door openings should be in line with the principal dwelling. Development must not be overbearing in scale or massing compared to the principal dwelling. Infill between buildings must not have a terracing effect.
Figure 44: Rear extensions, illustrative examples
Figure 44: Rear extensions, illustrative examples
Design principles - Rear extensions
Rear extensions should:
avoid a detrimental impact on the existing dwelling’s usable garden area;
not have a harmful effect on neighbouring properties in terms of privacy, overshadowing or overbearing impact;
provide an adequate distance between facing habitable rooms to help people feel comfortable in their homes;
comply with the 45-degree rule applying to two storey extensions only, as set out in this section.
Note: All design principles are applicable to all scales of development unless otherwise specified; *minor applications, **major applications
Front extensions, porches and canopies
p97.
Front extensions can often detract from the continuity of the street scene and damage the appearance of a dwelling.
p98.
Front extensions will be resisted where they have a significant impact on the street scene or are damaging to the appearance of a dwelling.
p99.
Where there is a prevailing rhythm to a series of buildings or strong building line, front extensions are unlikely to be acceptable.
p100.
Modest front extensions, where a building line is staggered or a dwelling is significantly set back from the road and reflects the character of the existing property, are more likely to be acceptable.
p101.
Front extensions should normally be designed with a pitched roof and match the main dwelling and its material.
p102.
Front extensions and porches should not become a dominant architectural feature and follow the same vernacular, material and detailing, including the size and rhythm of fenestration, including window casements and their style.
Key:
Acceptable in principle
Example of modest porch extensions in line with permitted development. Subservient in scale and massing, best practice is to preserve the principal dwelling and maintain its character. Materials and detailing should match the principal dwelling.
Potentially acceptable in principle
Example of a single-storey extension. Subservient in scale and massing, best practice is to preserve the principal dwelling and maintain its character, lean to extensions or dormer windows can be acceptable. Materials and detailing should match the principal dwelling.
Unlikely to be acceptable in principle
Example of a two-storey extension. Typically, larger front extension is unlikely to be accepted as they would substantially alter the principal dwelling. The proportion and rhythm of window or door openings should match the principal dwelling. Development must not be overbearing in scale or massing compared to the principal dwelling and the surrounding context and character, including any visual impact on the street scene.
Figure 45: Front extensions, illustrative examples
Figure 45: Front extensions, illustrative examples
Design principles - Front extensions, porches and canopies
Front extensions
Front extensions will be resisted where they have a significant impact on the street scene or are damaging to the appearance of a dwelling. Modest front extensions that reflect the character of the existing property are more likely to be acceptable. Large, flat-topped porches should be avoided. Where the building line is staggered or where the dwelling is set well back from the road, front extensions are more likely to be acceptable;
When located close to a neighbouring property, front extensions should not have a negative impact on the amount of light afforded to that property, nor should it have an overbearing impact;
Front extensions should not reduce the space available for parking below adopted standards outlined within Oxfordshire County Council Guidance.
Note: All design principles are applicable to all scales of development unless otherwise specified; *minor applications, **major applications
Loft and roof conversions
p103.
Loft conversions are a means of extending the existing living accommodation within a dwelling. As an enclosed space the main challenge of loft conversions is the introduction of roof lights or dormer windows for natural light and ventilation.
p104.
Dormer windows should be designed to sit evenly across the roof-slope and be set in from gable ends appropriately positioned between the eave line and ridge line. Two or three smaller dormers are often more successful than a single large dormer.
p105.
Dormer windows which extend a roof should be set within the roof slope. Where a clear rhythm of fenestration is established. Flat roofed dormers that fully occupy or extend the roof as a loft conversion should be avoided as they are considered visually detrimental and overbear to the massing of most dwellings.
p106.
Roof lights should follow the same principle, however, roof lights should not be positioned on the roof pitch of the front or primary elevation of a dwelling, as it detracts from the street scene.
p107.
Not all lofts are suitable for conversion, the pitch of a roof, width and depth of the building can limit the available space. All loft conversations require a minimum height of 2.2 metres, if your intended room has a sloping ceiling at least 50% of the floor area should achieve a floor-to-ceiling height of at least 2.1m.
p108.
Even if you have the required amount of headspace available in your loft, you may run into difficulties if you do not have enough space for a staircase up to it. Building regulations require a minimum of 1.9m of headroom at the centre of a flight of stairs, and 1.8m at the edges (where there will be sloping roofs). You will also need to allow space for the staircase on the floor below.
Key:
Acceptable in principle
Example of modest skylights and dormer windows forming a loft extension or conversion in line with permitted development. Subservient in scale and massing, best practice is to preserve the principal dwelling and maintain its character. The proportion and rhythm of skylights or dormer windows should match the principal dwelling. Materials and detailing should match the principal dwelling.
Potentially acceptable in principle
Example of larger or feature dormer windows forming a loft extension or conversion. These are to be considered in the context of local character and their visual impact. Subservient in scale and massing, best practice is to preserve the principal dwelling and maintain its character. The proportion and rhythm of skylights or dormer windows should match the principal dwelling. Materials and detailing should match the principal dwelling.
Unlikely to be acceptable in principle
Example of a full extension. Typically, larger front extension is unlikely to be accepted as they would alter the principal dwelling. The proportion and rhythm of window or door openings should match the principal dwelling. Development must not be overbearing in scale or massing compared to the principal dwelling and the surrounding context and character, including any visual impact on the street scene.
Figure 46: Roof extensions, illustrative examples
Figure 46: Roof extensions, illustrative examples
Design principles - Loft conversions and roof extensions
Loft conversions and roof extensions
Dormer roof extensions must be set within the roof slope. They should be designed as features principally to provide light and ventilation, and should sit well above the eaves line, well below the ridge line and should be set in from the gable ends. Dormer windows should not just be used as a means of generating additional headroom. The design should be informed by the character and appearance of the local vernacular;
The size, pitch and ridge height of dormers should be informed by the character and appearance of the existing building, and the local vernacular. The chosen design should complement the rhythm of the existing fenestration and roof pitch. The position and proportion of dormer windows should respond to existing windows and doors. Single, large flat roofed, box dormers must be avoided.
Roof lights should be used sparingly and where they are less likely to be visible in the street scene, such as to rear elevations or in discreet roof valleys. In sensitive locations, such as on Listed Buildings and in conservation areas, ‘conservation type’ roof lights should be used.
Note: All design principles are applicable to all scales of development unless otherwise specified; *minor applications, **major applications
Garages and outbuildings
p109.
These should follow the same general principles as extensions, principally the size and scale of any garage or outbuilding should not compete with the main dwelling.
p110.
The original building should remain the dominant element of the property whether you have one extension or several. The effect of any outbuilding should not overwhelm a dwelling from any given viewpoint.
p111.
The development of garages and outbuildings should not result in a significant loss to the private amenity area of the existing dwelling.
p112.
A single garage should be able to accommodate a car, storage and sufficient space for bicycles, with an internal floor area of 3 metres x 6 metres. A double garage should accommodate 6 x 6 metres.
p113.
Garages should not have domestic features or unnecessary fenestration (windows, dormers or rooflights). The Roof design of a garage should generally follow the same orientation to the gable of the main dwelling or utilise a pyramid roof.
Annexes
p114.
These are to provide self-contained accommodation or to offer a degree of separation from the main dwelling. However, they usually need to be linked to the main dwelling, both physically and in terms of the inter-dependence of the use of the annex and the main dwelling.
p115.
Residential annexes should be designed in accordance with the advice for other residential extensions. In addition, they should share the front door and entrance hall of the main dwelling, and they should be designed to be capable of being incorporated into the main dwelling at a later date.
p116.
Caution should be exercised to ensure that the conversion of an existing outbuilding to an annex does not result in the creation of a new dwelling. Where there is no clear link with the principle dwelling, development is unlikely to be acceptable.
Key:
Acceptable in principle
Example of modest garages single or double, attached or setback in line with the principal dwelling. The scale and massing of a garage should be proportional to that of the principal dwelling to maintain its character. Roof pitch should be reflective of that of the principal dwelling. Materials and detailing should match the principal dwelling.
Potentially acceptable in principle
Example of detached single or double garages, in line with the principal elevation. Flat roof garages are potentially acceptable if they do not detract from the principal dwelling character. The scale and massing of a garage should be proportional to that of the principal dwelling to maintain its character. Roof pitch should be reflective of that of the principal dwelling. This includes when detached and set within the curtilage of a property. Materials and detailing should match the principal dwelling.
Unlikely to be acceptable in principle
Detached single or double garages, when forward of the principal elevation, need careful consideration when set within the curtilage of a property. These should flank the principal dwelling wherever possible. Flat roof garages are unlikely to be acceptable in this context. The scale and massing of a garage should be proportional to that of the principal dwelling to maintain its character. Roof pitch should be reflective of the principal dwelling. Materials and detailing should match the principal dwelling. Domestic features should be avoided in particular where they detract from the principal dwelling.
Figure 47: Garages, illustrative examples
Figure 47: Garages, illustrative examples
Design principles - garages and outbuildings
Garages and outbuildings
Garages should be simple, functional buildings. They should be subservient to the main dwelling in terms of their scale, massing and height and should not include domestic features such as dormer windows (the standard size expected for garages to enable general storage are – internal dimensions of at least 6m x 3m for a single, 6m x 6m for a double);
Outbuildings should be visually subservient to the main dwelling when viewing the site from the wider surrounding area and should be sited so they are do not dominate the character of the street scene;
Outbuildings forward of the principle elevation will only be acceptable where they do not disrupt a clear and legible building line along the adjoining highway and/or break up the existing sense of enclosure along the street.
Note: All design principles are applicable to all scales of development unless otherwise specified; *minor applications, **major applications
