Merton Extensions 2026: Planning Guide, Costs & Permitted Development

Merton: What Kind of Borough Is It?

Merton is a south-west London borough covering a wide sweep of property types. Wimbledon — particularly Wimbledon Village and the streets around it — contains some of south London's most desirable Victorian and Edwardian detached houses and villas, many sitting in substantial plots with well-established gardens. The Village itself has an almost village-centre character, with older cottages and larger houses intermixed on winding roads above the common.

Raynes Park and Wimbledon Chase are dominated by inter-war and 1930s semis — bay-fronted, pebble-dashed or rendered, with generous rear gardens and side passages. These are among the most popular extension candidates in the borough: the plots are large enough to absorb a rear extension without sacrificing too much garden, and the absence of conservation area restrictions in many streets means permitted development rights often apply.

Merton Park and Colliers Wood retain rows of yellow London stock brick Victorian and Edwardian terraces — compact, tightly arranged streets where rear extensions and loft conversions are the primary way to add space. South Wimbledon has a similar character: dense terraced housing stock developed in the late Victorian period, now heavily owner-occupied and increasingly undergoing extension.

Mitcham and Morden offer greater variety — 1930s council-built housing alongside Victorian terraces, with a more suburban and mixed-tenure character. Costs in Mitcham and Morden sit at the lower end of the Merton range, while Wimbledon Village properties attract a premium for both property values and construction quality expectations.

Merton Local Plan and Extensions Policy

Merton's Local Plan is the primary planning policy document for the borough, replacing the former Core Planning Strategy (2011) and Sites and Policies Plan (2014). The plan runs until 2038 and sets out the policy framework against which all planning applications — including householder extensions — are assessed.

For residential extensions, the key supporting document is the Residential Extensions Supplementary Planning Guidance and the Urban Design SPD, which together provide detailed design criteria for extensions across the borough. These are read alongside the Local Plan policies when applications are assessed by Merton's planning officers.

Core design principles for Merton extensions

• Subordinate scale: Extensions must be subservient to the original building in height, mass, and width — particularly for side and rear extensions visible from the street
• Materials compatibility: In conservation areas, materials must be sympathetic to the original building. In Merton Park, this means matching yellow stock brick and maintaining the character of the Innes estate
• Neighbour amenity: Extensions must not cause unacceptable loss of daylight, sunlight, or privacy to adjoining properties — the 45-degree rule applies as a guide
• Street character: Front extensions and side returns visible from the road must respect the established building line and the character of the surrounding properties
• Garden retention: Adequate rear garden space should be retained. Merton officers will resist extensions that leave an inadequate garden for the property type

Conservation Areas and Article 4 Directions in Merton

Merton has a number of designated conservation areas covering historically significant parts of the borough. Within conservation areas, properties lose some permitted development rights by default — in particular, the right to clad external walls and to alter the appearance of the roof. More significantly, Merton has two old-style Article 4 directions confirmed by the Secretary of State in the John Innes Merton Park and Wilton Crescent conservation areas. These go considerably further in restricting what can be done without planning permission.

John Innes Merton Park Conservation Area

The John Innes Merton Park Conservation Area was designated in 1987 and covers the historic estate developed by John Innes in the late nineteenth and early twentieth centuries. It is one of the most distinctive planned residential areas in south London — tree-lined avenues, front gardens bounded by holly hedges, and a variety of high-quality Arts and Crafts and Edwardian houses. There are 145 listed buildings within the conservation area.

The Article 4 direction here (Article 4(2) directions No. 1 and No. 2, approved July 2007) removes permitted development rights for a wide range of external alterations, including extensions that would otherwise be permissible. One direction specifically requires planning permission for new dropped kerbs and crossovers — designed to protect the characteristic holly hedge boundaries and grass verges that define the area. If your property is in Merton Park, you should assume that almost any extension will require a full planning application.

John Innes Wilton Crescent Conservation Area

The John Innes Wilton Crescent Conservation Area, designated in 1984 and covering the area north of Kingston Road, was developed slightly earlier than the main Merton Park estate. It has a similar character — leafy streets, generous front gardens, and a mix of late Victorian and Edwardian houses. The Article 4 direction (Article 4(2) direction No. 2, confirmed by the Secretary of State in February 1990) removes permitted development rights for external alterations visible from the street.

There are 50 listed buildings within the Wilton Crescent area. Extensions in either John Innes conservation area require planning permission, and Merton planning officers will scrutinise proposals carefully for their impact on the character and appearance of the area. Pre-application advice is strongly recommended.

Wimbledon Conservation Areas

Wimbledon has several designated conservation areas covering its most historic streets. The Wimbledon Village Conservation Area runs from the borough boundary in the north to Parkside and Church Road in the south, and includes Wimbledon Common, Cannizaro Park, the High Street, and St Mary's Church. Properties here range from early cottages to large Victorian and Edwardian villas.

West Wimbledon, Wimbledon Broadway, and Wimbledon Chase are also covered by conservation area designations in parts. Extensions in these areas — particularly those affecting the front or side elevation — are subject to greater scrutiny on design quality and material choices. Rear extensions that are not visible from public viewpoints generally have a more straightforward path through the planning process, provided they are well designed.

Mitcham Conservation Area

The Mitcham Conservation Area covers a large and historically complex part of Mitcham town centre and the surrounding historic village area. It extends from Seely Road in the north through Phipps Bridge and down to Wandle Road in the south, and includes Cricket Green, Fair Green, and the Figges Marsh and Gorringe Park area. The area reflects Mitcham's long history as a market garden and coaching town.

Extensions in the Mitcham Conservation Area are assessed against the character appraisal for the area. The dominant building stock is a mix of Georgian and Victorian cottages and terraces, with some later inter-war housing. Materials in the historic core are typically yellow stock brick or render, with clay tile or slate roofs.

Other Conservation Areas in Merton

Permitted Development in Merton

Outside of conservation areas and Article 4 direction zones — primarily in Raynes Park, Wimbledon Chase, parts of Morden, and much of south and east Mitcham — the standard national permitted development rights for householders apply. These allow certain extensions to be built without a full planning application.

The Planning Process in Merton

Standard householder planning applications in Merton are decided within 8 weeks. More complex applications, including those in conservation areas or involving listed buildings, may take up to 13 weeks. Most householder extensions are decided by officers under delegated authority — they do not go to planning committee unless they are controversial or the officer recommends refusal.

Note that Merton Council has flagged short delays to processing of some applications received in early 2026 due to an IT system upgrade. If your application is time-sensitive, factor this into your programme and contact the planning department to confirm current processing times.

Pre-application advice

Merton offers a pre-application advice service for homeowners. The standard householder pre-application service costs £250 including VAT, which covers a one-hour virtual meeting with a planning officer. Additional time is charged at £180 per hour pro-rata. For more complex proposals — including conservation area extensions and those involving listed buildings — budget for a more extended engagement.

Merton also offers a fast track service for applicants who want a quicker decision. This involves payment of an additional fee on top of the standard application fee and provides a dedicated case officer and a target decision date of 6 weeks for householder applications.

Pre-application advice is strongly recommended for extensions in Merton Park, Wilton Crescent, Wimbledon Village, and Mitcham conservation areas. Officers can indicate the scale, materials, and design approach that is likely to be supported before you commit to full design drawings, significantly reducing the risk of refusal or requests for amendments.

Application fees (2026)

• Householder application: £258 (England, from December 2023)
• Prior approval (large rear extension): £120
• Listed building consent: No fee (fee-exempt)
• Pre-application advice (householder): £250 including VAT (1-hour meeting)

Design Requirements by Area

Merton Park: the John Innes estate character

Merton Park is unlike almost anywhere else in south London. The John Innes estate was designed as a coherent whole — varied in its architecture but unified by trees, hedges, and a consistent quality of materials. The dominant building type is Edwardian and Arts and Crafts detached and semi-detached houses, typically in red or yellow London stock brick with tile-hung gables, timber casement windows, and front gardens screened by holly hedges.

Extensions in Merton Park are scrutinised for their impact on the individual building and on the character of the conservation area as a whole. Rear extensions in matching brick, set behind the building line and subordinate in height, fare well. Contemporary designs in steel and glass at the rear can be approved where they are clearly of high quality and do not affect key views. Anything affecting the front elevation — including porch extensions or side garages facing the street — is highly likely to require planning permission and faces significant scrutiny.

Wimbledon Village: setting and materials

Wimbledon Village has an exceptionally varied building stock — from modest Victorian cottages to large Edwardian and inter-war detached houses. Extensions here are assessed against the conservation area character appraisal and Merton's design guidance. The key considerations are scale (extensions must not overwhelm the original building), materials (matching or sensitively contrasting), and impact on views from the Common and adjacent public space.

Rear extensions in Wimbledon Village are generally the most viable route. Well-designed single-storey rear extensions with large glazed openings are regularly approved, particularly where materials are of high quality and the extension does not increase ridge height. Two-storey rear additions face a higher bar and require careful attention to scale and massing relative to the existing building.

Raynes Park and Wimbledon Chase: 1930s semis

Outside the conservation areas, Raynes Park and Wimbledon Chase offer the most straightforward planning environment in Merton. The largely 1930s semi-detached stock — bay-fronted, with side passages and generous rear gardens — is well-suited to rear extensions. Permitted development rights apply in many streets, meaning single-storey rear extensions up to 3m deep on semis (or 6m prior approval) can often proceed without full planning permission.

Side return extensions, loft conversions, and two-storey rear additions are popular in this area and regularly approved where they meet Merton's design criteria. The larger plots associated with 1930s development mean that garden retention is rarely a problem for single-storey extensions.

Colliers Wood and South Wimbledon: Victorian terraces

Colliers Wood and South Wimbledon are characterised by yellow London stock brick Victorian terraces — compact, tightly spaced, with narrow side passages and modest rear gardens. Extension options here are more constrained than in the suburban semis of Raynes Park, but rear extensions and loft conversions are consistently popular and achievable.

Side return extensions that infill the narrow passage between the terrace and the boundary wall are a common project type, creating L-shaped ground floors that significantly open up kitchen and living space. These are generally well-received by Merton officers where they are set back from the rear building line and do not affect the street elevation.

Extension Costs in Merton 2026

All costs below are inclusive of VAT at 20% and reflect 2026 market rates for south-west London contractors. Merton sits in a mid-to-upper cost band for London — typically 5–10% higher than outer south-east boroughs but similar to Wandsworth and Kingston. Wimbledon Village properties attract the highest rates, reflecting both the premium property values and the higher quality of finish expected. Conservation area work adds 10–15% to accommodate premium materials and specialist brickwork.

Additional professional and statutory costs

• Architect or architectural designer: £4,500–£14,000 (typically 8–12% of build cost; higher for Wimbledon Village projects)
• Structural engineer: £1,500–£3,500
• Planning application fee: £258 (householder)
• Party wall surveyor: £1,500–£3,000 per adjoining owner (essential for terraced properties in Colliers Wood and South Wimbledon)
• Building Control: £800–£2,000 depending on project scale
• Pre-application advice (Merton Council): £250 including VAT (standard householder service)

Common Extension Types by Neighbourhood

Wimbledon Village and West Wimbledon: high-quality rear extensions

The larger detached and semi-detached houses in Wimbledon Village and West Wimbledon lend themselves to ambitious rear extensions — both single and two-storey. Kitchen-dining extensions with full-width bifold or sliding glazed doors opening onto the garden are the dominant typology. Given the property values in this area, build quality expectations are high: architects are almost always employed, and clients typically specify high-end finishes including Crittall-style steel glazing, natural stone flooring, and kitchen joinery exceeding £50,000 on its own.

Raynes Park and Wimbledon Chase: side and rear extensions on semis

The 1930s semis of Raynes Park and Wimbledon Chase are well-suited to both rear extensions and loft conversions. The standard rear extension project here adds 3–4m to the back of the house to extend the kitchen-dining area into the garden. Many properties in these streets retain their original side passages, making side return infills viable. Loft conversions adding one or two bedrooms are the second most common project — the hipped roofs on many 1930s semis are frequently converted to gable ends as part of the works.

Colliers Wood and South Wimbledon: Victorian terrace rear extensions

The Victorian terraces of Colliers Wood and South Wimbledon see the most side return extensions and loft conversions in Merton. A typical project in these streets adds a single-storey side return extension to extend the ground floor kitchen-dining room, combined with a dormer loft conversion to create one or two additional bedrooms. These two projects combined typically cost £110,000–£160,000 and can add very significant value in a neighbourhood where properties were historically undervalued but are now attracting strong buyer interest.

Merton Park: careful conservation area design

Merton Park extensions are a specialist area. The strong conservation area protections mean that design quality is paramount — both in terms of planning approval likelihood and in preserving the character of the estate that makes these properties so desirable. Successful extensions here tend to be single-storey rear additions in matching brick or carefully considered contemporary materials, set clearly behind the building line and not affecting the front or side elevations visible from the tree-lined avenues. Budget additional time for pre-application advice and the planning process, and appoint an architect familiar with Merton's conservation area policies.

Mitcham and Morden: value-focused extensions

Mitcham and Morden offer the most accessible entry point for extensions in Merton from a cost perspective. Property values here are lower than Wimbledon and Merton Park, but there is strong demand from buyers for extended properties with good kitchen-dining space. The planning environment outside the Mitcham conservation area is generally straightforward, and permitted development rights apply in many streets. A well-executed rear extension or loft conversion here can add disproportionate value relative to build cost.

Planning Tips for Merton Extensions

• Merton Park: treat this as a conservation area project from the outset. With 145 listed buildings and comprehensive Article 4 directions, extensions in Merton Park almost always require planning permission. The £250 pre-application advice meeting is well worth the investment before committing to a design approach. Officers here are knowledgeable about the estate character and will give clear steer on what is and is not likely to be supported.
• Check for TPOs before any design work near trees. Tree Preservation Orders are particularly common in Wimbledon Village, Merton Park, and along the Wandle. Work affecting roots or canopy within three times the tree's trunk radius typically requires consent. Merton's tree officers can advise — but it is better to identify constraints before your architect finalises the layout.
• Party walls are essential for Colliers Wood and South Wimbledon terraces. Merton's Victorian terraces have shared party walls on both sides. You must serve notice on both adjoining owners before starting any excavation or structural work. If both neighbours appoint their own surveyors, this process can take 3–4 months and cost £3,000–£6,000. Factor this into your timeline and budget from the beginning.
• Wimbledon Village: appoint an architect with conservation area experience. Not all architects are equally comfortable with the requirements of conservation area design. In Wimbledon Village, a strong heritage and design narrative in the planning submission significantly improves the chances of approval — particularly for anything that is contemporary or unconventional in approach. Officers here are receptive to good modern design, but poorly presented proposals face a harder road.
• Consider Merton's fast track service for straightforward proposals. For well-prepared applications on properties outside conservation areas where the design is unambiguous, Merton's fast track service can reduce decision time to 6 weeks. This is particularly useful if you are working to a programme driven by school year timings, lease expiry, or another external deadline.
• Always verify permitted development status before starting work. Even outside the named conservation areas, Merton has streets with local designations or covenants that affect what can be built. Use Merton's planning map or our free AI checker to confirm the status of your address before committing to a design that assumes permitted development rights apply.