Extensions in London Conservation Areas: What You Can and Can't Build

**What is a conservation area?**

A conservation area is a designated area where the local planning authority (the London Borough) has decided that the character and appearance of the built environment is sufficiently special to warrant additional protection. In London, conservation areas protect a wide range of environments — Georgian and Victorian terraced streets (Islington, Hackney, Kensington); inter-war suburban areas (parts of Barnet, Richmond, Bromley); industrial heritage areas (parts of Bermondsey, Wapping); and post-war planned estates. The character that is protected varies significantly between areas.

**How to check if your property is in a conservation area**: The simplest way is to search the local London Borough's planning interactive map (most London boroughs have a GIS mapping tool on their website that shows all designated areas including conservation areas, Article 4 Directions, listed buildings, TPO trees, and flood zones). The property search on the local authority's planning portal will also show designation status. The title deeds do not normally record conservation area status — the local authority's records are the authoritative source.

**What changes for extensions in a conservation area**:

*Permitted development (PD) rights — most remain*: Many permitted development rights that apply to residential properties apply equally in conservation areas. Extensions that would be permitted development outside a conservation area are often still permitted development within one. However, there are important exceptions:

*What is RESTRICTED in conservation areas (PD rights removed or limited)*:

1. *Side extensions*: In conservation areas, the construction of any side extension is NOT permitted development — a full planning application is required for ANY side extension, regardless of size. This is one of the most significant differences from properties outside conservation areas.

2. *Cladding the exterior*: In conservation areas, changing the materials of the exterior of the main house or any outbuilding is NOT permitted development — a planning application is required to change facing materials, rendering, cladding, or tile hanging on the principal elevation.

3. *Roof alterations — front-facing dormers*: In conservation areas, any alteration to the roof that is visible from the highway in front of the property requires planning permission. This means: a front-facing dormer (which would be PD elsewhere) is NOT PD in a conservation area. Rear dormers are still PD in most London conservation areas (subject to standard PD conditions — within 40m³ for terraced, 50m³ for other house types, not higher than the highest part of the roof, must use similar materials).

4. *Outbuildings and garden buildings visible from a highway*: Some outbuilding PD restrictions are tightened in conservation areas.

*What is the SAME as outside a conservation area (generally)*:

1. *Rear extensions*: Single-storey rear extensions remain PD in conservation areas, subject to the same depth limits (up to 3m for terraced/semi, 4m for detached from the original rear wall under standard PD; up to 6m or 8m under the prior approval Neighbour Consultation Scheme). The materials condition (similar in appearance) applies.

2. *Rear dormers*: As noted above, rear dormers are generally still PD in conservation areas subject to the standard volume and height conditions.

3. *Rooflights*: Rooflights on the rear slope of the roof are PD in conservation areas (subject to not projecting more than 150mm above the plane of the roof and not being higher than the ridge). Rooflights on the front slope visible from the highway require planning permission in conservation areas.

4. *Small porches*: Porches up to 3m² and not higher than 3m remain PD in conservation areas.

**Article 4 Directions — where even more PD rights are removed in London conservation areas**:

• Many London boroughs have additionally applied Article 4 Directions to properties in conservation areas, which remove further permitted development rights. The most commonly removed right under Article 4 in London conservation areas is:
• •*Class A extensions (rear extensions)*: Some boroughs remove PD rights for even small rear extensions in conservation areas, requiring planning permission for ALL rear extensions regardless of size
• •*Class B and C roof alterations*: Some boroughs remove PD rights for all roof alterations (including rear dormers and rooflights) in conservation areas
• •*C3 → C4 change of use*: Many boroughs with high HMO concentrations apply Article 4 to remove PD change of use rights in conservation areas

*Examples of London boroughs with extensive Article 4 coverage in conservation areas*: Kensington and Chelsea, City of Westminster, Islington, Hammersmith and Fulham, Camden.

The only way to confirm which PD rights apply to a specific property in a London conservation area is to check the specific borough's Article 4 Direction mapping for that conservation area. What applies in one conservation area in one borough may not apply in another conservation area in a neighbouring borough.

**How London conservation area officers assess extension proposals**:

When a planning application for an extension in a conservation area is assessed, the conservation area officer (and the planning case officer) applies the following tests:

1. *Does the proposal preserve or enhance the character and appearance of the conservation area?* This is the statutory test under section 72 of the Planning (Listed Buildings and Conservation Areas) Act 1990. The proposal must not cause 'harm' to the character or appearance of the conservation area — either through poor design, inappropriate scale, or use of materials that do not harmonise with the existing character.

2. *Is the proposal subservient to the original building?* Conservation area officers typically want extensions to read as subordinate to the host building — smaller in scale, set back from the principal facade, and designed so they do not visually dominate the original property. This is sometimes called the 'subservience principle'.

3. *Are the materials appropriate?* Materials should either match or harmonise with the original building. In London's Victorian terrace conservation areas, this means London stock brick (yellow/buff), red brick (in East London Victorian streets), or render matching the original. Modern materials (zinc, aluminium cladding, dark timber) can be acceptable if the design justification is strong — but they are harder to get through in traditional areas.

4. *Is the roofline and form appropriate?* Flat roof extensions to the rear are generally well-accepted in London conservation areas for single-storey extensions (provided they are not visible from the street). Pitched roof extensions that match the original pitch and ridge height are also generally supported. Contemporary flat-roofed or mono-pitch extensions visible from the street can be contentious.

**The 'visible from the street' test**:

A key practical consideration in London conservation area planning is visibility from the street (the 'public domain'). Extensions and alterations that are not visible from any street, highway, or public footpath are generally viewed much more favourably than those that are prominent in the street scene. A rear extension hidden by the house is unlikely to cause harm to the character of a conservation area even if it is larger or more modern in appearance than the host building.

**Materials guidance for London conservation area extensions**:

• *Brickwork*:
• •Match the original building's brick specification as closely as possible — London stock brick, red brick, yellow brick, or grey brick depending on the building period and location
• •Brick matching is challenging — order samples from brick reclamation yards (London has many specialist suppliers of period brick) before committing to a specification
• •Mortar should also match — colour, texture, joint profile (struck, flush, or raked as per original)
• •Conservation area officers often request brickwork sample panels on site before approving the full extension construction

• *Render and stucco*:
• •Where the original building has render or stucco, an extension in matching render is appropriate
• •Cement render is no longer acceptable in conservation areas where lime render was original — lime-based renders (NHL 3.5 or similar) are required by many conservation officers
• •Colour should match the existing render (or be agreed with the conservation officer)

• *Glazing*:
• •Aluminium or timber framing is acceptable in most London conservation areas
• •uPVC is generally NOT acceptable in conservation areas
• •Black aluminium framing is frequently requested by London conservation officers where the original building has black painted ironwork
• •If replacing windows in a conservation area (not just in an extension), original timber sash windows should generally be retained or replicated — modern casement windows do not match Victorian sash windows and are typically refused for principal elevations

• *Roofing*:
• •New pitched roof sections should use materials matching the original — plain clay tiles or natural slate in most London conservation areas; concrete tiles or synthetic slate are generally not acceptable where original materials are clay or natural slate
• •Flat roof extensions: visible flat roofs should use appropriate materials — mineral felt (with a decent finish) is generally accepted; standing-seam zinc or lead-look GRP can be acceptable where a more finished appearance is required

**Pre-application advice in London conservation area applications**:

For any extension in a London conservation area that requires planning permission, pre-application advice from the local authority is strongly recommended — and in some cases practically essential. London boroughs offer pre-application services for householder applications at costs ranging from £100–£500 per consultation.

• The benefits of pre-application advice in a conservation area context:
• •The conservation officer gives early guidance on whether the proposed design and materials are likely to be acceptable — identifying issues before the application is prepared (and before planning drawings are fully developed)
• •If pre-application advice supports the proposal, it is a strong positive indicator for the formal application (though it does not guarantee approval)
• •Pre-application advice from the conservation officer can be referenced in the Design and Access Statement / Heritage Statement that accompanies the formal application, demonstrating that the applicant engaged proactively with the authority's conservation concerns

**The Design and Access Statement (DAS) and Heritage Statement**:

For planning applications in conservation areas (even householder applications), a Heritage Statement or Design and Access Statement explaining how the proposal responds to the character and appearance of the conservation area is strongly recommended — and required in some London boroughs.

• A Heritage Statement for a conservation area extension typically covers:
• •Description of the conservation area and the property's contribution to its character
• •Analysis of the existing building and its significance
• •Description of the proposed extension — form, scale, materials, relationship to the original building
• •Analysis of the impact of the proposal on the character and appearance of the conservation area
• •Conclusion explaining how the proposal preserves or enhances the conservation area

*Who produces the Heritage Statement?* For complex conservation area applications (listed buildings, prominent sites, sensitive areas), a heritage consultant or conservation architect (AABC-registered) is appropriate. For standard householder applications (rear extension, rear dormer), the Heritage Statement can often be produced by the applicant's architect as part of the planning application package.

**The Conservation Area Appraisal — the planning authority's character document**:

• Every designated conservation area should have a Conservation Area Appraisal (CAA) and a Management Plan produced by the local authority. These documents define:
• •The special character and appearance that the conservation area protects
• •The positive elements of the area (building styles, period, materials, street patterns)
• •The negative elements (inappropriate alterations, poor-quality infill, missing features)
• •Design guidance for new development and alterations

The CAA is available from the local authority's planning department and is a critical reference document for any conservation area extension application. The proposal should be explicitly designed to respond to the CAA's character description — and the Heritage Statement should reference the CAA.

**Enforcement in conservation areas — what happens for unauthorised works**:

Carrying out works in a conservation area without the required planning permission is a planning breach. The local authority can serve an Enforcement Notice requiring the removal or reinstatement of unauthorised works. For conservation areas (as opposed to listed buildings), there is no criminal offence for unauthorised works to unlisted buildings — but enforcement can require demolition of an unauthorised extension or restoration of original materials.

For works that are genuinely within permitted development (or genuinely not requiring permission), there is no enforcement risk. But where the position is uncertain (especially in conservation areas with extensive Article 4 coverage), a Certificate of Lawfulness (for Proposed Development — CLOPUD) is the safe option. A CLOPUD application to the local authority confirms whether the specific works require permission or not — and provides a document that can be used in future conveyancing to demonstrate that the works were lawful.

Additional note: Conservation area status is distinct from listed building status. Unlisted buildings within a conservation area are subject to conservation area planning policy but are NOT subject to the additional protections of listed building consent. Works that affect the character of a listed building require Listed Building Consent regardless of conservation area status.