Basement plans in Blackheath, Forest Hill and Hither Green

Which postcode districts around Lewisham do we cover for basement extension work?

Every Lewisham postcode district we draw in, the stock that dominates it and the authority that validates a basement extension there. Lewisham fees below are the statutory England rates for 2026, not basement extension estimates.

How does a basement extension differ street by street across Lewisham?

Roof pitch, wall build-up and plot depth change every few Lewisham streets, and each one changes what a basement extension can achieve at that address.

• Hither Green (SE13) — basement extension work in Hither Green means edwardian terraces, 1930s semi-detached. Hither Green is Edwardian terraces, 1930s semi-detached. Edwardian houses rarely have a usable cellar throughout SE13. Lewisham Council decides the Hither Green application, and Mountsfield Park anchors the Hither Green location plan.
• Sydenham (SE26) — Victorian villas, Edwardian terraces defines Sydenham, where victorian villas, edwardian terraces set what a basement extension can do. Victorian cellars here convert without planning permission when the footprint and external appearance are unchanged across SE26. Any Sydenham basement extension is validated by Lewisham Council, with Sydenham Wells Park the usual Sydenham reference point on the site plan.
• Brockley (SE4) — Victorian and Edwardian terraces defines Brockley, where victorian and edwardian terraces set what a basement extension can do. Victorian cellars here convert without planning permission when the footprint and external appearance are unchanged across SE4. Any Brockley basement extension is validated by Lewisham Council, with Brockley station the usual Brockley reference point on the site plan.
• Forest Hill (SE23) — basement extension work in Forest Hill means victorian villas, edwardian terraces. Forest Hill is Victorian villas, Edwardian terraces. Victorian cellars here convert without planning permission when the footprint and external appearance are unchanged throughout SE23. Lewisham Council decides the Forest Hill application, and Horniman Museum anchors the Forest Hill location plan.
• Honor Oak (SE23) — Victorian villas on the hill defines Honor Oak, where victorian villas, edwardian terraces set what a basement extension can do. Victorian cellars here convert without planning permission when the footprint and external appearance are unchanged across SE23. Any Honor Oak basement extension is validated by Lewisham Council, with One Tree Hill the usual Honor Oak reference point on the site plan.
• Lewisham (SE13) — basement extension work in Lewisham means victorian terraces, post-war flats. Lewisham is Victorian terraces, post-war centre. Victorian cellars here convert without planning permission when the footprint and external appearance are unchanged throughout SE13. Lewisham Council decides the Lewisham application, and Lewisham station anchors the Lewisham location plan.
• Blackheath (SE3) — a basement extension in Blackheath starts from georgian villas, victorian terraces, and Blackheath reads as Georgian and Victorian villas around the heath. Georgian houses here already have a vault and a lower-ground floor in SE3. Lewisham Council assesses Blackheath basement extensions against its own Blackheath character guidance, and the location plan we draw for Blackheath references Blackheath.

Does Lewisham planning policy restrict a basement extension?

Lewisham conservation designations: there are 30 across Lewisham Council, Hither Green, Lee Green, Blackheath among them. Designation costs a Lewisham owner the permitted-development route: a basement extension then needs a £548 householder application over 8 weeks, in place of the £249 prior approval route that takes 6 weeks. Hither Green is the Lewisham designation that most often changes a basement extension design.

Article 4 and your Lewisham basement extension: Lewisham Council has made no borough-wide direction, so permitted development for a basement extension in Lewisham generally survives outside Lewisham conservation areas and listed curtilages. A Lawful Development Certificate at £274 is how a SE4 owner records that a basement extension was lawful.

The building fabric around Lewisham: Victorian and Edwardian terraces across Brockley, Honor Oak, Forest Hill; 1930s semi-detached in Catford and Hither Green; post-war mixed in Deptford. Generally permissive planning compared to central boroughs; loft conversions and side-return extensions routinely approved under PD. A basement extension in Lewisham is scoped against that stock first.

Which neighbouring authorities border Lewisham?

• Southwark — adjoining Lewisham, with 43 conservation areas centred on SE1. A basement extension on the far side of the Lewisham line is determined by Southwark Council, so the Lewisham quote for basement extensions is checked against Southwark guidance before it is issued.
• Greenwich — adjoining Lewisham, with 20 conservation areas centred on SE3. A basement extension on the far side of the Lewisham line is determined by Greenwich Council, so the Lewisham quote for basement extensions is checked against Greenwich guidance before it is issued.
• Bromley — the Bromley boundary runs against Lewisham, so a basement extension a street from Lewisham is decided by Bromley Council instead. Bromley runs 48 conservation areas across BR1 and its neighbours, which is why basement extensions priced for Lewisham are re-checked against Bromley policy whenever the Lewisham address sits on that edge.
• Tower Hamlets — cross the Lewisham boundary and Tower Hamlets Council takes the basement extension instead, applying 58 conservation areas of its own around E1. We re-price basement extensions at the Lewisham edge because Tower Hamlets policy and Lewisham policy rarely align on basement extension depth.

Sources for this Lewisham basement extension page: borough policies maps and conservation-area registers (2025–26), Royal Mail postcode district boundaries, the Town and Country Planning (Fees for Applications) (England) Regulations, the Town and Country Planning (General Permitted Development) (England) Order 2015 as amended, and the Party Wall etc. Act 1996.