1 Introduction

The Brighton and Hove City Plan contains planning policies that are used to determine planning applications for new development. Planning policies set out how development proposals can be supported to make sure good quality development is achieved. The City Plan is available on the Council’s website, and relevant policies should be consulted before making a planning application for any extension or alteration. It may also be helpful to look up your address using the Council’s on-line map to see if there are any area-specific constraints relevant to the property.

Supplementary Planning Documents (SPDs) are produced to provide additional guidance, information or clarification on how the requirements of local planning policies can be met. SPDs do not carry as much weight as the City Plan policies but can be useful, additional guidance in preparing and assessing planning applications.

Any extension or alteration to a property requires careful thought in terms of planning and design in order to ensure it has a good fit with the existing environment.

It is also useful to discuss initial ideas for an extension or an alteration to a property with neighbours. All planning applications are subject to public consultation, so it is best to iron out any neighbour concerns at an early stage, however, agreement with the neighbour does not imply the application will be automatically approved.

It may be helpful to consider appointing an accredited professional to assist in drawing up the scheme or the planning application. The Royal Town Planning Institute (RTPI), Royal Institute of British Architects (RIBA), the Royal Institution of Chartered Surveyors (RICS) and Charted Institute of Building (CIOB) all provide details on their website of all accredited professionals.

A checklist at Appendix 1 of this document provides guidance on what documents, plans, photographs and details should be submitted as part of a planning application.

How your application will be assessed

In determining planning applications the Council will make an assessment against adopted local and national planning policies, whilst having regard to other material considerations including this SPD. There are three main considerations outlined by planning policy that relate to extensions and alterations:

  • Achieving high-quality design;
  • Neighbourly development; and
  • Delivering Sustainability.

Further details on each of the considerations above are outlined within this Supplementary Planning Document. If the proposed works constitute significant changes to the property, consider engaging with the Council prior to submitting the planning application by applying for Pre-application advice. (Please see the Council’s website for further information on applying for Pre-application advice including what fees and documentation are required.)

Using this SPD

This document offers guidance on how to comply with relevant planning policies and achieve the best possible extension or alteration. When developing a proposal, it is important to balance your own needs with the needs and rights of neighbours and also consider what is best for the wider community. This guide has been structured to help to achieve this balance. The document is set out as follows:

  • It begins by stating the need to understand the local character of Brighton and Hove and how acceptable extensions and alterations may differ depending on where they are (Section 2);
  • It then outlines some general design principles applicable to all alterations and extensions (Section 3), before giving more detailed, project specific guidance and standards (Section 4);
  • This document also sets out additional guidance on extensions and alterations involving listed buildings or those set within a Conservation Area (section 5). Applicants considering such proposals are encouraged to engage with and seek early advice from the Council’s Heritage team through the pre-application service or review the information on the Heritage pages of then Council’s website.

This guide ends with advice on further information to be submitted to assist the application and a glossary explaining the meaning of technical terms used.

Permitted Development Rights

Some extensions and alterations may not require planning permission. This is known as ‘Permitted Development’. Permitted development rights are detailed in the Town and Country Planning (General Permitted Development) Order 2015 (as amended). The permitted development rights have changed over time and they can sometimes be quite complicated to interpret.n Permitted development rights usually do not apply to: residential buildings which are not single dwelling houses, flats, listed buildings, or where there are planning conditions in place specifically removing permitted development rights relating to planning permissions. If the property is within a Conservation Area or an Article 4 designation, the ‘permitted development’ rights of the property will be affected. It will be useful to look at the guidance on permitted development rights available at the Planning Portal website.

This SPD is also a useful tool to achieve a high quality of design from extensions and alterations that fall within permitted development.

2 Understanding Local Context

Understanding the local context will help proposals for extensions and alterations to take account of the important qualities and characteristics of the neighbourhoods or streets which help define them.

The city contains many residential areas and neighbourhoods each with their own distinctive identity and characteristics. The particular challenges for extensions and alterations therefore vary across different townscape types within neighbourhoods or streets, as do the opportunities. Streets, for example, are often characterised by a common design based upon the repetition of an architectural style and/or a setting which establishes a distinctive building rhythm.

It is acknowledged that some areas can accommodate change more easily by virtue of being more diverse in character compared to others. Some areas, due to their elevated position, may be more sensitive than others. This document recommends examining in detail the local context for any proposed development and relating the new extension/alteration to its surroundings.

Some areas of the city have been designated as conservation areas due to their special architectural or historic interest. Some individual buildings have been deemed so important that they have been statutorily listed. It is useful to check whether the property being extended is within a conservation area or is a listed building before making any plans for changes. A street directory of all conservation areas within the City can be found at on our website. This is particularly important as conservation areas may have special planning controls that apply. In all cases stricter policies special planning controls that apply. In all cases stricter policies apply to any alterations. Additional considerations relating to conservation areas, listed buildings and locally listed buildings are set out later in this document.

High density Victorian terrace in the Hanover area of Brighton

High density Victorian terrace in the Hanover area of Brighton

Detached single dwellings in the Hangleton area of Hove

Detached single dwellings in the Hangleton area of Hove

Semi-detached properties in West Hove

Semi-detached properties in West Hove

3 General Principles

This section outlines general principles for achieving a good design and therefore a well-designed extension or alteration.

A. Achieving High Quality Design

It is important that extensions and alterations should have an attractive design and complement the character and appearance of the original property and, where relevant, the group of buildings of which it forms a part.

  • In general achieving high-quality design is about ensuring that an extension or alteration has regard to the host building and its surroundings in terms of scale, mass, height, siting, character, choice of materials and spacing;
  • An extension should be appropriately positioned, scaled and materially finished such that it would relate sympathetically to the architectural character of the building and the wider area;
  • As a rule of thumb new extensions should be subservient to the original property. One way of achieving this is, for example, by stepping the extension back (or in) from building lines to create a clearer distinction between the form of the original building and the extension. An appropriate extension should not impose or intrude upon the original or neighbouring dwelling;
  • A relationship with the streetscene needs to be carefully considered. Building line, pattern, roof lines, pitch and shapes of roofs, views and orientation are all important considerations. For example, new extensions should respect the symmetry of semi-detached pairs and be comfortably accommodated within the terrace of which it forms a part;
  • The front elevation and other parts of the property visible from the street are normally more sensitive to change than other parts of the property that are not visible. Corner properties, due to their higher visibility from the street require more attention in designing an appropriate extension.
  • Sometimes it may be more appropriate to design an extension using a sensitive but contemporary design with contrasting materials such that the extension is clearly identifiable from the original building. In such cases the design and materials used should still be of the highest quality and demonstrate a strong response to the original building.

In Conservation Areas and where high quality historic buildings require extensions, it may be more appropriate to generally seek to introduce or retain the prevailing architectural features and character of the area. Where original architectural details to the property have been lost, these should be reinstated to enhance the character of the property and the wider streetscene. In most cases, new windows, doors and other details such as choice of materials should reflect the design and alignment of the existing fenestration of the building. More detailed guidance is available for properties in Conservation Areas in Section 5 of this document.

B Neighbourly Development

Neighbours have the right to enjoy their home without intrusion from inappropriate development at adjoining properties. Extensions and alterations will be expected to be designed to be respectful of neighbours’ privacy, daylight and outlook. Proposals should avoid loss of daylight or overshadowing of adjoining properties. In particular loss of light to main windows serving principal rooms (such as living rooms, bedrooms and kitchens) will be an important consideration.

Proposals should:

  • Avoid direct overlooking into neighbouring habitable rooms (including kitchens) and the private outdoor amenity spaces. Garden spaces that are closest to the property are the most sensitive areas;
  • Ensure the extension does not appear overbearing by keeping the overall bulk minimal so that the extension does not appear visually dominating or intrusive to an adjacent property;
  • Where relevant, respond to topography and land level changes in their design to minimise their impact upon adjacent properties;
  • Balconies and roof terraces should be discreetly located to avoid overlooking and noise disturbance to adjacent properties;
  • Consider the scale, massing, height and the size of the extension including its positioning generally to ensure the new extension has a good fit with adjacent properties.

If you are intending on building or fixing anything directly on or close to the boundary of your property you are advised to refer to the Party Wall Act (which is a separate piece of legislation, not relevant to Planning and is a private civil matter), which relates to issue around land ownership and maintenance.

Rear extension: Fraher Findlay Architects – responding to topography

Rear extension: Fraher Findlay Architects – responding to topography

C Delivering Sustainability

Extensions and alterations should be designed and constructed to deliver sustainable development which respects the environment. They are an opportunity to incorporate renewable energy sources and to potentially provide some urban greening to the property and to contribute to reducing Carbon emissions.

  • Consider design that helps to promote and enhance biodiversity. Subject to the character of the area, methods of achieving this might include the use of green/living roofs, green walls, planting, and garden landscaping. Extensions and alterations should actively seek to incorporate new methods to support local wildlife, including installation of bee bricks, bat and swift boxes where appropriate and feasible and in accordance with local guidance;
  • It is a good practice to check any building before the extension or alteration work commences to establish if there are any active swift nests within the building and whether they need replacement or relocating. Further Council guidance is available regarding orientation and number of bricks/boxes suitable for different scales of development;
  • Established trees, hedges and other natural features should be preserved, replaced/relocated or their loss appropriately mitigated. Any adverse impact on neighbouring trees should be avoided. Trees in Conservation Areas and those with Tree Preservation Order (TPO) are subject to additional protection;
  • Extensions and alterations should be energy efficient and incorporate renewable energy sources
  • All new paving, driveways and patio areas should be constructed from permeable materials or incorporate sustainable urban drainage techniques to reduce surface water run-off.

Useful References:

City Plan Part 1 Policy 10 CP10 Biodiversity, Brighton & Hove City Council, 2016 · Supplementary Planning Document (SPD11) – Nature Conservation and Development, Brighton and Hove City Council, 2010

A box for swifts to nest in and a brick with holes available for bees to shelter

Examples of the many types of integrated bee and swift habitats

A biosolar roof - combining solar energy with biodiverse green roof habitat

A biosolar roof - combining solar energy with biodiverse green roof habitat

4 Detailed Guidance

The detailed guidance set out below is not exhaustive or definitive. Its purpose is to guide the design of new extensions/alterations to enable a better fit with the host building as well as minimise any visual intrusion on the street scene or character including avoiding harm to neighbours’ amenity. Variations to these guidelines may be acceptable where it can be demonstrated that no harm is caused to existing neighbouring amenity or to the character of the local area. Innovative and contemporary solutions that enhance a sense of scale, proportion and place are encouraged.

Rear extensions

The Council will seek to ensure that rear extensions are of a suitable scale to remain subservient to the character and appearance of the main property and are sensitively designed. Particular care is needed if the property is located at the end of a terrace or is a corner property as an extension to the rear is likely to be visible from the street. The following guidance should be followed where relevant:

  • Rear extensions should generally be subservient to the host property, however, for properties with a very large overall plot size larger extensions can sometimes be considered appropriate;
  • Rear extensions should not have an overbearing impact or cause adjacent properties to be excessively overshadowed or enclosed. The bulk of the extension alongside the shared boundary should therefore be kept to a minimum;
  • All rear extensions should comply with the 45 degree rule (see Appendix 3). This rule ensures there will not be an unacceptable loss of daylight to the neighbouring properties;
  • Rear extensions must not overhang neighbouring properties and should not replace the boundary wall/fence (unless the adjacent property has an existing extension themselves and the loss of the wall is required for better maintenance purposes);
  • In the majority of cases rear extensions (both single and two storey) should not extend beyond the main side walls of the building (including all projections/wings);
  • The ridge of the pitched roof of a single storey rear extension should sit lower than the cill of the first floor windows;
  • Flat roofs can be suitable for single storey rear extensions particularly where they integrate well with the host building;
  • Two storey rear extensions should generally have a roof form which reflects that of the host building. A pitched roof extension should normally be set lower than the main ridge of the roof;
  • Where side-facing windows are required for light, they should generally be high level, permanently fixed shut or obscurely glazed to prevent the overlooking of neighbouring properties.
  • Materials used in the extension should be sympathetic to the character of the area and the property being extended;
  • Rear extensions should ensure that a suitable amount of rear garden/amenity area is retained.

Lean-to rear extension: Archangels Architects, Brighton & Hove

Lean-to rear extension: Archangels Architects, Brighton & Hove

Two storey rear extension: LW Architects, Brighton & Hove

Two storey rear extension: LW Architects, Brighton & Hove

Side extensions

Spacing between buildings helps to define the character of an area. Side extensions therefore should ensure that rhythm of spacing between buildings is maintained in order to minimise the potential ‘terracing’ effect. In terms of semi-detached and terraced properties, the proposed extension should avoid unbalancing the attached properties.

  • The following guidance should be followed where relevant: Side extensions should be set back from the front elevation appropriately in order to ensure a subordinate appearance (and set down from the roof ridge in the case of a two storey side extension). The setback and setdown helps to avoid the terracing effect and enables the extension to be read as subservient to the original building;
  • Side extensions should complement the original property. The width of a side extension should respect the width of the original property and the overall plot size in which it is located to avoid it appearing over-extended;
  • The design, detailing, and materials used in the extension, including window position/pattern, sizes, proportions, style and method of opening, should complement those of the main building;
  • The incorporation of a roof form which matches the character and materials of the host property and surrounding area will often be considered to be most acceptable;
  • The residential amenity of adjoining residents will be a particularly important consideration when assessing side extensions. Flank windows should not allow overlooking and may have to be permanently fixed shut and fitted with obscure glazing (or obscure glazed blocks) and kept to a minimum. Windows, roof eaves, gutters or downpipes should be avoided on party walls for planning purposes so that extensions do not intrude on neighbouring properties or restrict their future extension;
  • For detached properties appropriate set-in should be provided between the site boundary and the extension retaining a proportionate amount of space. Where the property is located in a more spacious plot, a greater separation may be more appropriate to complement the character of the area;
  • Infill extensions should not have an overbearing impact or cause adjacent properties to be excessively overshadowed or enclosed. The bulk of the extension alongside the shared boundary should therefore be kept to a minimum, and as close to 2 m in height as reasonably possible on the boundary;
  • Infill extensions must not overhang neighbouring properties and should not replace the boundary wall/fence (unless the adjacent property has an existing extension themselves and the loss of the wall is required for better maintenance purposes);
  • Corner properties should ensure an active and attractive street frontage. Corner plot side extensions should also respect the building lines to both streets, and be set within existing boundary treatments.

Front extensions (Including porches)

Extensions to the front of buildings will normally be highly visible in the streetscene therefore particular care should be taken to ensure they do not detract from the appearance of the property, or the general character of the street. Particular regard should be given to the materials, detailing, prevailing building lines and fenestration of front extensions to ensure they relate well to the original building and the streetscene.

  • The following guidance should be followed where relevant: All front extensions should respect the building line to the street, particularly where a strongly defined building line forms an important character of the area;
  • A front extension should not dominate the existing façade or any important architectural feature that already exists in the original building;
  • The roof pitch of the extension should complement the pitch of the original building so that the extension blends with the character of the building.
  • A small porch is generally acceptable on most building types provided it does not compete with other architectural features on the building and is of the right scale and proportion;
  • Even an extension that is subservient in size can add an incongruous shape or form that is out of character with the front elevation of the property or the surrounding area. Careful attention should be given to the style as well as the size and proportion of any front extension.

An example of a two storey front extension

An example of a two storey front extension

An example of a discreet porch extension

Roof alterations

The rhythm and continuity of the rooflines to buildings are often a key visible element within a streetscene therefore any poorly designed or excessively bulky additions can have a significantly harmful impact on both the appearance of the property and the continuity of a streetscape. In addition, consider the following guidance:

  • Extensions involving roof alterations should ensure that they would not result in an imbalance between the semi-detached pair or in a small terrace. A well-designed alteration that returns symmetry to the pair may be acceptable
  • Additional storeys or raised roofs may be permitted on detached properties where they respect the scale, continuity, roofline and general appearance of the streetscene, including its topography;
  • Roof extensions that alter the basic shape of the roof are likely to have an impact on the streetscene. Such alterations should reflect the character of roof forms in the surrounding area.

Dormer windows

A dormer is a window that is typically set vertically on a sloping roof. The dormer has its own roof, which may be flat, arched, hipped, gabled, or ornamented. Dormers can add elegance and appeal to the property, but they can also end up making the property look out of proportion, so the design should be carefully considered in line with following guidance:

  • Dormer extensions are expected to avoid appearing unduly bulky or visually harmful, and should not materially disrupt the rhythm and continuity of the prevailing roofline in the area;
  • The most appropriate roof design of a dormer (gabled/hipped/flat/eyebrow) will vary depending upon the character of the host property and surrounding area;
  • Where a terrace or group was built with dormers, these original features should not be removed or altered. Where a terrace or group was originally designed without dormers, but over the years a majority of the buildings now have them, new dormers may be acceptable provided their scale, design and positioning is sympathetic to the continuity of the terrace/group;
  • Generally, the cladding, glazing, framing and any ornamentation on the dormer window should match the existing property.

Rear and side dormer windows

Dormer windows on the rear roof slope will normally have limited or no impact on the streetscene, however, they should clearly be a subordinate addition to the roof set appropriately in the roof space to avoid looking disproportionate to the property.

As a rule rear dormers should be appropriately set in from the side, set down from the ridge and set up from the eaves so as not to appear as an additional storey or appear “top heavy”. In addition, further consideration should be given to ensure that:

  • Rear dormer windows do not appear above the ridge line of the dwelling;
  • Rear dormer windows are generally well-proportioned to the roof space and do not appear overly dominant. Where two or more dormers are proposed they should be evenly aligned and spaced within the roofspace;
  • Rear dormer windows should normally align with the windows below, however, in certain cases it may be preferable for dormers to be positioned on the centre line of the building;
  • Materials of the window frames, roofing and cladding should match or relate well to those of the existing roof or the property; 
  • Well-designed side dormers are acceptable where they do not compromise the character of the building or the street and/or the privacy of a neighbouring property.

Front dormer windows

Dormer windows on the front roof slope will have a greater impact on the streetscene. Front dormer windows should be sensitively designed to respond to their prominent setting. Depending on the character of the street, front dormers may be acceptable, and where acceptable they will generally be limited to a single dormer extension. Exception may be made in some areas of the City where front dormer windows are a common feature and where the size of the property can comfortably accommodate more than one dormer.

Front dormers should be:

  • Set-back appropriately from the eaves of the main building;
  • Set-down down appropriately from the ridge;
  • Designed with a roof and materials to complement the host property.

Normally it is expected that dormer positioning will align well with the windows below. As in the case of rear dormers in certain cases it may be preferable for dormers to be positioned on the centre line of the building or the centre line of the space between the windows below.

Balconies and roof terraces

Balconies and roof terraces can provide valuable and welcome amenity space for properties; however, in many cases they can significantly affect a neighbour’s privacy and create a sense of overlooking, particularly if they are located where it is possible to look into gardens or windows that previously enjoyed privacy. The presence of balconies and roof terraces may also result in noise disturbance, particularly to nearby windows, and can also be harmful to the appearance of a building. Careful consideration needs to be given to the location and design of a balcony or a terrace including any associated balustrades

Balconies and roof terraces at the front and rear of the building including any other prominent locations visible from the street are only acceptable where they do not harm the appearance of the building and streetscene.

The urban character of certain parts of Brighton and Hove means some properties already overlook one another. Balconies and roof terraces that create new overlooking or make existing situations much worse are unlikely to be approved. In such cases screening can provide the required privacy to all parties but their detailing and size must also be appropriate to the character of the building and area.


The construction of outbuildings in rear gardens and other undeveloped areas can often have an impact upon the amenity, biodiversity and character of an area.

The siting, location, scale, materials and design of the outbuilding should have a minimal visual impact on, and be comfortably accommodated within the host garden. The maximum size of the outbuilding (or number of outbuildings) will usually be determined by the location and the size of the garden area.

  • Irrespective of the size of the outbuilding proposed, the open character and outlook of the rear garden should be maintained;
  • Outbuildings will normally be restricted to a single-storey so that they do not harm the amenity of neighbouring homes and gardens. The maximum permitted height will normally be determined by the impact on residential amenity and the proximity of the outbuilding to the neighbouring boundaries, on both sides and to the rear.
  • The intended use of the outbuilding will be a consideration so as to ensure the development respects the use and character of an area.

New and replacement windows

The character of a property can be enhanced by the alteration or addition of new windows or doors that align with the style and character of the original. Good quality window design and placement can contribute to the general appearance of buildings, help maintain the rhythm of the streetscene, particularly on large blocks of flats and more traditional building forms where the continuity of fenestration is a key element. New and replacement windows should:

  • Complement the appearance and character of an existing building / terrace, closely matching original details, frame styles and materials where possible.
  • Align well with the existing windows in terms of size, design, rhythm and pattern of openings in terms of window positioning, and orientation;

In most cases windows positioned to match the symmetry of those in the existing building help maintain the aesthetics and character of the building.


The size, design and siting of rooflights should not significantly change the appearance of the building externally and should not introduce detrimental visual elements into the streetscene.

  • Roof lights (particularly to street elevations) should be kept as few as possible and should relate well to the scale and proportions of the elevation below, including aligning with windows or centering on the spaces between them where appropriate;
  • Where two or more rooflights are proposed they should be evenly aligned and spaced within the roofspace;

Irregular rooflight sizes and positioning should be avoided, and in particular will be resisted on street elevations.

Minor alterations

Boundary walls, hedges and fences

Garden walls, fences, railings and hedges are all important elements in the streetscene. They provide the distinction between the private space and the public space of the pavement and street.

Differing boundary treatments along a street can result in a cluttered, disordered appearance. This effect is particularly noticeable in streets of terraced or semi-detached houses. Alteration of front boundary walls and fences will need to:

  • Be constructed from materials in sympathy with the building or surrounding area;
  • Respect the height of other enclosures in the street so to not appear unduly conspicuous and out of character;
  • Consider well maintained planting as an attractive and green solution for a new boundary; Safeguard pedestrian and vehicular safety.

The design and height of boundary walls (including pillars), railings and gates should relate to the character of the street/surrounding area, particularly if of a uniform character. Details such as railed sections and pillars can reduce the visual impact of a high wall. The removal of a front boundary wall or hedge and the development of the front garden into a forecourt for parking will be resisted where it would have an adverse impact on visual amenity or the character of the streetscene.

Satellite dishes, cables, ducts and pipework

Satellite dishes and aerials including cables, ducts and pipeworks can add visual clutter and detract from the appearance of a building and streetscene if located in a prominently visible position. It is therefore important to ensure that:

  • Satellite dishes and aerials are sited in the most unobtrusive position possible and not be located on walls, chimneys or roofs visible from the street;
  • The number of dishes should be reduced where possible to avoid the visual clutter;

All cables, ducts and pipework should run internally or up the rear wall in discrete positions and be coloured/painted to match the background wall. Flues, ventilation units and other services that appear as 'add-on' elements will not normally be accepted in elevations visible from streets.

5 Extensions and alterations in historic buildings and conservation areas

Some additional considerations relating to Conservation Areas, listed buildings and locally listed buildings are set out below but proposals should also take account of the policy guidance in SPD09 on Architectural Features.

Listed Buildings

Brighton & Hove has over 3,400 listed buildings which are of special architectural or historic interest. Where a building has been listed, it is listed in its entirety, which means that both the exterior and the interior are protected. The listing includes any object or structure fixed to the building (such as railings or boundary walls), and any object or structure within the curtilage of the building, which although not fixed to the building, forms part of the land and has done so since before 1 July 1948. Formal ‘Listed Building Consent’ is required from the Council for any works that would affect a building’s special character, alongside an application for planning permission (if required). A directory of all Listed Buildings within the City can be found at http://www.brighton-hove.gov.uk/index.cfm?request=c1001398. It is worth noting that:

  • The detailed advice in this guide is not intended for listed buildings. Applications for works to listed buildings will always be treated on a case-by-case basis outside of the general guidance contained within this document, as the acceptability of such schemes is strongly dependent upon the individual character, form, layout and detailing of the building;
  • In general, proposals for extensions and/or alterations to listed buildings will be expected to demonstrate that the significance of the building has been understood and conserved, and will be expected to show an exceptional level of design quality and detailing. 

Conservation Areas, Buildings of Local Interest

Many buildings within Brighton & Hove are located within Conservation Areas and/or have been identified as buildings of local interest. A street directory of all Conservation Areas within the City can be found at http://www.brighton- hove.gov.uk/index.cfm?request=c1001585. Any proposal for extension or alteration therefore must seek to preserve or enhance, and not cause harm to, the special character or appearance of the area. Proposals for extensions and alterations that affect historic buildings and those in Conservation Areas are expected to demonstrate

  • A clear understanding of the importance of the historic street pattern, building form, layout, design and materials of these buildings and areas;
  • A high level of design and detailing that would preserve or enhance their significance for future generations.
  • Adherence to the Conservation Area Character Statement for that area (if one is in place) which sets out the significance of a Conservation Area including what makes it special.

Side, rear and front extensions in a conservation area

Extensions and alterations to Buildings of Local Interest and buildings within conservation areas should be completed to a high design standard, with materials and detailing matching those of the host building. The council will expect the submission of material samples and design details where appropriate, for approval as part of the application. In addition consider following guidance:

  • Side extensions and rear infill extensions will not be acceptable where they would result in the loss of symmetry of a historic building, symmetrical pair or group of historic buildings, or result in excessive disruption or loss of the original plan form of the building;
  • The roof form and pitch of an extension should normally reflect the host building’s roof form and pitch, when visible from the street, and be clearly read as a subordinate addition to the building;
  • In some cases historic buildings with pitched roofs have flat roofed rear extensions and where this is typical of a terrace or group it may well be acceptable to follow this precedent;
  • Front extensions are unacceptable in principle to historic buildings within a Conservation Area and the original front façade should be retained generally unaltered;
  • Porches are not acceptable unless it can be shown that the building was originally intended to have one, whilst unnecessary clutter from new flues, pipes and cables will not be permitted on street elevations;
  • In general a more flexible approach will be taken in respect of rear elevations that are not publicly visible, particularly where the rear of a terrace or group has been subject to past incremental alteration that has eroded its significance;
  • Modern design approaches and finishes may be acceptable where it can be demonstrated the scale and exceptional design quality of the extension would enable the special character of the host building or the area to be most appropriately conserved. For example, a modern, lightweight approach can be appropriate for infill extensions where this would enable the original building form to be more clearly distinguished.

Extension of a listed building: Landivar Architects, Patcham, Brighton

Extension of a listed building: Landivar Architects, Patcham, Brighton

Roof Extensions and Alterations

On historic buildings the roof is often the ‘crowning glory’ and an integral part of the overall design. Alterations to the shape or form of the roof, the use of unsympathetic materials and the loss of original features can all have a serious effect on the appearance and character of historic areas. The additional following guidance applies:

  • Roof extensions, including dormers, respect the particular architectural character of the building and should be carefully related to it. Not all roof spaces will be suitable for extension/alteration to provide additional accommodation; for example those with shallow or limited roof pitches;
  • The original form, shape and fabric of the main roof are not to be altered and its ridge height is not to be raised. Exceptions to this may only be considered where the roof is not a visible feature of the building and its alteration would not harm the integrity of the wider area.
  • Alteration of a pitched roof to form a roof terrace is normally not acceptable;
  • Where a street has developed with buildings of varying height and scale, and where a varied roof-line is an important aspect of its character, this should be respected, and any tendency to level up buildings to a uniform height will be resisted;
  • Original or historic decorative features at roof level, including dormers, party wall upstands, ridge tiles and lantern lights should always be retained, and where appropriate, re-instated.

Dormer Windows and Rooflights

Traditional dormers or rooflights were located to provide a small amount of daylight and ventilation to the loft or attic rooms, or to provide access onto a valley roof for maintenance purposes. Larger ones were sometimes used to light a stairwell. Lantern lights were often also used where more light was required to stairwells and other areas. Historically, rooflights were small and confined to rear roof slopes or hidden valleys. Where significant amounts of daylight are needed for rooms in the roof space, a dormer window is often a more architecturally and historically appropriate solution, but

  • Front dormers will not be considered appropriate unless typical of the street;
  • Inset dormer windows will usually be acceptable on the rear roof slopes, but only rarely on the front or side;
  • All dormer windows should be finished with moulded eaves, cornices and timber fascias. Rooflights will usually be acceptable on rear roof slopes, and on occasion, the sides;
  • Front rooflights are rarely acceptable unless typical of the street;
  • All rooflights should be ‘conservation rooflights’ (double or single glazed) which lie flat in the roofs.

Rooflights on a listed building's conservatory

Listed building extension: PCMS Design, South Oxfordshire

New and Replacement Windows

On historic buildings windows contribute to the character of the building through their design, materials and workmanship. Any proposal for new or replacement windows should note that:

  • Plastic or aluminium replacement windows will not be acceptable on elevations visible from the street where the original windows were designed to be timber;
  • In cases where such windows already exist and need to be replaced the council will seek the re-instatement of appropriate timber windows;
  • In many cases timber windows can acceptably incorporate double glazing. Further guidance on fenestration within historic buildings can be found within SPD09 Architectural Features, and this will be used to guide decision making

Replacement windows on a listed building: ABIR Architects, Lewes

Replacement windows on a listed building: ABIR Architects, Lewes

6 Appendices

Appendix 1: Planning Application Requirements

Upon receipt of an application for planning permission, officers will undertake an initial consideration of the proposed development. It is important that the information provided to the Council clearly demonstrates how the extension or alteration to the property is being proposed. Mandatory requirements The following documents are mandatory requirements for most planning applications including householder planning applications and must be provided with your application at the point it is made:

  1. Application Form
  2. Application Fee
  3. Location Plan (1:1250 or 1:2500)
  4. Site / Block Plan (1:100/200/500) (Must show the proposed extension in relation to existing buildings on and adjoining the site, areas and boundaries of site, including detail of access points, trees and hard-surfacing)
  5. Existing Floor Plans, Roof Plans & Elevations (1:50/100)
  6. Proposed Floor Plans, Roof Plans & Elevations (1:50/100)
  7. Sections & Site Levels (1:50/100) Further information on all of the above can be found on the Council’s website.

Desirable additional information

It will be helpful to officers if the following documents, drawings and photographs are submitted with the application (in addition to the mandatory requirements):

  1. Site Photographs;

    • A photograph showing the relevant elevation of the property being extended. (e.g. for a rear extension the photograph should be taken from the rear garden looking back towards the property showing both neighbouring properties);
    • A photograph showing the outlook from the proposed extension. (e.g. for a rear extension the photograph should be taken from the back door/ window/first floor window looking towards the back of your garden);
    • A photograph of any other relevant angles/elevations you consider to be helpful to officers in their initial consideration of your application.
  2. 3D Visualisation or Isometric Drawing. 3D drawing is usually not necessary but can be helpful in interpreting a complicated scheme.
  3. A brief written summary of any other matters you wish to draw to the attention of the planning officer.

Appendix 2: Glossary

Article 4 Direction

Direction removing some or all permitted development rights, for example within a Conservation Area or curtilage of a listed building. Article 4 directions are issued by local planning authorities.


The whole variety of life encompassing all genetics, species and ecosystem variations, including plans and animals.


A term relating to Conservation Areas or Listed Buildings but also to the appearance of any rural or urban location in terms of its landscape or the layout of streets and open spaces, often giving places their own distinct identity.

Conservation Area

Local authorities have the power to designate as conservation areas, any area of special architectural or historic interest. This means the planning authority has extra powers to control works and demolition of buildings to protect or improve the character or appearance of the area. Conservation Area Consent has been replaced by planning permission for relevant demolition in a conservation area.


Part of a roof that meets or overhangs the walls Flank window: A side window Gable: The vertical triangular end of a building from eaves to ridge

Hipped roof

Pitched roof where two roof planes meet at the ridge

Listed Building

A building of special architectural or historic interest. Listed buildings are graded I, II* or II with grade I being the highest. Listing includes the interior as well as the exterior of the building and may include buildings or permanent structures (e.g. wells within its curtilage)

Locally listed building

Locally important building valued for contribution to local scene but not meriting listed building status

Obscure glazed

Opaque glass reducing visibility


A term used to describe the impact where the effect is dominating


A term used to describe the effect when a development or building affords an outlook over adjoining land or property often causing loss of privacy


The effect of a development or building on the amount of natural light presently enjoyed by a neighbouring property resulting in a shadow being cast over that neighbouring property


Top line of the roof Terracing effect: A term used to describe the closing of gaps between houses by extending the houses sideways

Tree Preservation Order (TPO)

A mechanism for securing the preservation of single or groups of trees of acknowledged amenity value. A tree subject to a tree preservation order may not normally be topped, lopped or felled without the consent of the local planning authority

Appendix 3

When designing an extension it is important to consider the level of sunlight and daylight currently enjoyed by the neighbouring properties. Extensions that are poorly designed and sited can result in unacceptable impact on neighbour’s amenities. It is a common practice to use the 45-degree rule to measure such impact. The 45 degree rule is set out in the Building Research Establishment (BRE) document ‘Site Layout Planning for Daylight and Sunlight: A guide to good practice (2011) and is an accepted rule of thumb test to determine whether or not further detailed daylight and sunlight tests are required.

The primary concern of the 45-degree test is the level of light and unobstructed view from a habitable room window. Rooms such as bathrooms, halls, utilities and landings/stairs do not require this consideration. Whilst this test is more common to residential dwellings it is also suited to non-residential properties, where occupants have a reasonable expectation of daylight, for example schools, hospitals, hotels, offices and workshops.

The 45 degree test normally works for extensions that are perpendicular to a window in a neighbouring property. A centre line is marked on the plan of the neighbouring window that may be affected by the extension. A 45 degree angle is drawn from the outer most part of the extension toward the window. If the 45 degree line extends above or beyond the centre line of the window, there is a chance there will be an adverse effect on daylighting in the neighbouring property. If the 45 degree line does not extend beyond the centre point of the window, it would suggest the neighbouring property would continue to receive adequate natural daylight and would not be affected by the proposal.

Plan diagram showing footprint area in inside the 45 degree projections

Elevation diagram showing footprint area inside the 45 degree projections