Lewisham Extension Guide 2026: Planning Permission, Costs & Conservation Areas

Lewisham: What Kind of Borough Is It?

Lewisham sits in south-east London and covers a varied mix of housing stock. Brockley, Forest Hill, and Honor Oak are dominated by Victorian and Edwardian terraces — long rows of two- and three-storey properties with original stock brick facades, slate roofs, and rear gardens backing onto each other. These streets are among the most photographically consistent in south London and are why Brockley holds one of the largest conservation areas in the borough.

Lee and Grove Park shift to 1930s semis and inter-war housing — more suburban in character, with larger plots and more permissive planning conditions. Blackheath, straddling the boundary with Greenwich, has Georgian and early Victorian townhouses and villas set around the Heath, with a distinctly grander character than the terraced streets to the west.

This variety matters when planning an extension. The rules — and the design expectations — differ substantially between a Victorian terrace in Brockley and a 1930s semi in Grove Park. Knowing which regime applies to your property is the first step.

Lewisham Local Plan and Extensions Policy

The Lewisham Local Plan 2020–2040, adopted in July 2025, is now the primary planning document for the borough. It replaces the previous Core Strategy (2011) and Development Management Local Plan (2014). All planning applications are now assessed against this updated plan.

For householder extensions, the key supporting document is the Alterations and Extensions Supplementary Planning Document (SPD). Adopted in 2019 and read alongside the new Local Plan, this document sets out the design principles Lewisham applies to all residential extensions, whether permitted development or planning permission is required.

Core design principles from the Lewisham SPD

• Subordinate scale: Extensions should be visually subordinate to the original building — in height, width, and massing
• Matching or complementary materials: Particularly important in conservation areas, where materials must respect the original building fabric
• Neighbour amenity: Extensions must not cause unacceptable loss of light, outlook, or privacy to adjoining properties
• Street character: Front and side extensions visible from the street should respect the established building line and character of the terrace or road

Conservation Areas and Article 4 Directions

Lewisham has a significant number of designated conservation areas. In several of them, the council has applied Article 4 directions that remove permitted development rights. This means external alterations visible from the street — including rear extensions in some cases — require planning permission rather than proceeding under permitted development.

Brockley Conservation Area

The Brockley Conservation Area is one of the largest in the borough, designated in 1973 and covering a wide swathe of Victorian terraced streets. An Article 4 direction was made for Brockley in 2006, specifically to control small-scale but cumulatively damaging changes — the replacement of sash windows with uPVC, the removal of front boundary walls, and alterations to roofing materials that erode the uniform character of the terraces.

The dominant building material is yellow London stock brick, with Welsh slate roofs. Extensions in this area are expected to use materials that complement this palette — reclaimed or matching stock brick for rear extensions, or high-quality contemporary materials (dark metal, timber cladding) that contrast deliberately without undermining the heritage character. Lewisham officers take this seriously: pre-application advice is strongly recommended before submitting any extension in Brockley.

Blackheath Conservation Area

The Blackheath Conservation Area was designated in 1968 — the first conservation area in London. It straddles the Lewisham and Greenwich boundary, with approximately three quarters falling within Lewisham and one quarter in Greenwich. Extensions in the Lewisham portion are determined by Lewisham Council; properties in Greenwich fall under Greenwich's planning department.

Blackheath has a grander, more formal character than Brockley — Georgian and Victorian villas set around the Heath, with consistent fenestration patterns, proportions, and materials. Extensions here face strict design scrutiny. Rear extensions must be subordinate and must not disrupt the roofline or massing of the original building when viewed from public spaces.

Other Conservation Areas in Lewisham

Permitted Development in Lewisham

Where Article 4 directions do not apply — primarily in the more suburban areas of Lee, Grove Park, and parts of Catford and Lewisham town — the standard national permitted development rules for householders apply.

The Planning Process in Lewisham

Standard householder planning applications in Lewisham are decided within 8 weeks. Major applications take up to 13 weeks. Planning committee meetings are held every two weeks, though the majority of householder extensions are decided by officers under delegated powers and do not go to committee.

Pre-application advice

Lewisham offers a pre-application advice service for homeowners. The Duty Planner Standard Service costs £136.18 (inc. VAT) from April 2025 and covers a face-to-face session with a planning officer. A follow-up query by email costs £68.09 (inc. VAT). For more complex cases, the Duty Planner Complex Service is £241.34 (inc. VAT).

Pre-application advice is strongly advisable for extensions in Brockley and Blackheath conservation areas. Officers will indicate what materials, scale, and design approach they are likely to support, which significantly reduces the risk of refusal.

Application fees (2026)

• Householder application: £258 (England, from December 2023)
• Prior approval (large rear extension): £120
• Listed building consent: No charge (fee-exempt)

Design Requirements by Area

Brockley: Victorian terrace design

Extensions in Brockley are assessed against the conservation area character appraisal and the Lewisham Alterations and Extensions SPD. The appraisal identifies yellow London stock brick as the predominant material, with Welsh slate roofs and stucco detailing. Successful extensions here typically take one of two approaches: matching stock brick with traditional-profile roof tiles for a seamless addition, or a clearly contemporary rear extension with high-quality contrasting materials — dark steel, frameless glazing, or charred timber — that reads as a deliberate new addition without competing with the original facade.

Lewisham officers are generally supportive of good contemporary design at the rear, where it is not visible from the street. Extensions visible from the front or side of a conservation area property face considerably higher scrutiny.

Blackheath: formal Georgian and Victorian character

Blackheath requires extensions to respect the formal proportions of the original buildings. Heights must be kept below the eaves line; extensions should not alter the silhouette of the building when viewed from the Heath or surrounding streets. The joint character of the area — shared with Greenwich — means that proposals affecting the boundary zone may be viewed in the context of both boroughs' conservation area policies.

Forest Hill and Ladywell

Forest Hill Conservation Area covers a diverse mix of building types. Article 4 directions apply across the whole area. Extensions here are expected to respect the character of the local streetscape — Edwardian bay-fronted semis on one road, Victorian terraces on another. Ladywell, with its tight Victorian terracing, typically sees rear extensions and loft conversions rather than side extensions, given the constrained plot widths.

Extension Costs in Lewisham 2026

All costs below are inclusive of VAT at 20% and reflect 2026 market rates for south-east London contractors. Lewisham sits in a mid-range cost band for London — typically 5–10% lower than central zones such as Camden or Kensington, but higher than outer south-east suburbs. Conservation area work typically adds 10–15% to accommodate premium materials and additional detailing.

Additional professional and statutory costs

• Architect or architectural designer: £4,000–£12,000 (typically 8–12% of build cost)
• Structural engineer: £1,500–£3,500
• Planning application fee: £258 (householder)
• Party wall surveyor: £1,500–£3,000 per adjoining owner (shared walls common in terraces)
• Building Control: £800–£2,000 depending on project scale
• Pre-application advice (Lewisham): £136–£241 depending on service level

Common Extension Types by Area

Brockley and Honor Oak: Victorian rear extensions and lofts

The long, narrow terraced properties in Brockley and Honor Oak lend themselves naturally to rear extensions and loft conversions. A single-storey rear extension extending the kitchen-dining room into the garden is the most common project type, typically 3–4m deep, with a flat or lean-to roof and a large rear glazed opening. Dormer loft conversions adding a bedroom and bathroom above are the second most frequent project. Side return extensions — infilling the narrow alley between the house and boundary wall — are also common where the side passage runs the full depth of the ground floor.

Blackheath: strict rear extension design

Extensions in Blackheath are almost always to the rear — the formal front elevations of Georgian and Victorian properties are not candidates for alteration. Rear extensions are typically single-storey with flat or shallow-pitched roofs, set below the original eaves line. Officers are attentive to materials: render or brick that reads sympathetically against the original rear elevation is preferred over highly contemporary finishes in the most sensitive settings. However, good contemporary design can be approved where it is clearly of high quality.

Forest Hill: side returns and rear extensions

Forest Hill has a mix of Victorian terraces and larger Edwardian semis, many with side passages. Side return extensions that wrap around the rear are common and popular, creating L-shaped ground floors that open up kitchen and living space dramatically. These typically require planning permission within the conservation area. The full Article 4 direction here means even small rear extensions that would otherwise be permitted development need an application.

Lee and Grove Park: 1930s semis

Outside the conservation areas, Lee and Grove Park offer more flexibility. The larger plots associated with 1930s semis typically allow for more substantial rear extensions, and the absence of Article 4 directions in many streets here means permitted development rights often apply. Single-storey rear extensions up to 6m deep may proceed without planning permission on detached properties, subject to the standard height and materials conditions.

Planning Tips for Lewisham Extensions

• Brockley conservation area: use pre-application advice. Given the Article 4 direction and the strong character appraisal for the area, submitting without pre-app guidance risks a refusal on materials or scale. A £136 duty planner session can save months of delays.
• Blackheath: check which borough applies. If your property is in the Greenwich portion of the Blackheath Conservation Area, your application goes to Greenwich Council, not Lewisham. The conservation area policies are similar but the officers and fee schedules differ.
• Never assume permitted development. Even outside the named conservation areas, there are streets in Lewisham with local Article 4 directions or TPOs. Use Lewisham's online planning map or our free checker to verify your specific address before starting design.
• Party wall notices are essential for terraced properties. Lewisham's Victorian terraces invariably have shared party walls. You must serve notice on adjoining owners before beginning any excavation or structural work. Allow 2–4 months for this process if neighbours appoint their own surveyor.
• The new Local Plan (adopted July 2025) now takes precedence. If you received pre-application advice before July 2025, it is worth checking whether the new plan has changed any relevant policies before submitting your application.