Chislehurst plots make a basement viable across Bromley

Which Bromley postcodes does this basement extension service cover?

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

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

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

• West Wickham (BR4) — a basement extension in West Wickham starts from 1930s semi-detached, and West Wickham reads as 1930s semi-detached. 1930s houses were built without cellars in BR4. Bromley Council assesses West Wickham basement extensions against its own West Wickham character guidance, and the location plan we draw for West Wickham references West Wickham station.
• Biggin Hill (TN16) — a basement extension in Biggin Hill starts from 1930s semi-detached, and Biggin Hill reads as 1930s semi-detached, rural fringe. 1930s houses were built without cellars in TN16. Bromley Council assesses Biggin Hill basement extensions against its own Biggin Hill character guidance, and the location plan we draw for Biggin Hill references Biggin Hill Airport.
• Keston (BR2) — a basement extension in Keston starts from edwardian villas, 1930s semi-detached, and Keston reads as Edwardian and 1930s village. Edwardian houses rarely have a usable cellar in BR2. Bromley Council assesses Keston basement extensions against its own Keston character guidance, and the location plan we draw for Keston references Keston Ponds.
• Penge (SE20) — a basement extension in Penge starts from victorian and edwardian terraces, and Penge reads as Victorian and Edwardian terraces. Victorian cellars here convert without planning permission when the footprint and external appearance are unchanged in SE20. Bromley Council assesses Penge basement extensions against its own Penge character guidance, and the location plan we draw for Penge references Penge East station.
• Bromley (BR1, BR2) — Victorian and Edwardian centre defines Bromley, where victorian terraces, edwardian villas, post-war flats set what a basement extension can do. Victorian cellars here convert without planning permission when the footprint and external appearance are unchanged across BR1. Any Bromley basement extension is validated by Bromley Council, with Bromley High Street the usual Bromley reference point on the site plan.
• Beckenham (BR3) — basement extension work in Beckenham means edwardian villas, 1930s semi-detached. Beckenham is Edwardian villas, 1930s semi-detached. Edwardian houses rarely have a usable cellar throughout BR3. Bromley Council decides the Beckenham application, and Beckenham Junction anchors the Beckenham location plan.
• Chislehurst (BR7) — basement extension work in Chislehurst means 1930s detached, edwardian villas. Chislehurst is Large 1930s detached, conservation. Edwardian houses rarely have a usable cellar throughout BR7. Bromley Council decides the Chislehurst application, and Chislehurst Caves anchors the Chislehurst location plan.

How do conservation areas and Article 4 affect a basement extension in Bromley?

Conservation areas covering Bromley: Bromley Council runs 48, and Keston, Bickley, Bromley Town are the ones Bromley owners meet most. A basement extension inside a Bromley conservation area loses permitted development, so the Bromley submission is a householder application at £548 decided in 8 weeks — not a £249 prior approval decided in 6 weeks. In Chislehurst a basement extension is judged on the street elevation first.

Article 4 and your Bromley basement extension: Bromley Council has made no borough-wide direction, so permitted development for a basement extension in Bromley generally survives outside Bromley conservation areas and listed curtilages. A Lawful Development Certificate at £274 is how a SE20 owner records that a basement extension was lawful.

Bromley housing stock: Large 1930s detached and semi-detached in Chislehurst and Bickley; Edwardian in Beckenham; Victorian in Bromley town; Metropolitan Green Belt covers significant rural-fringe land. Largest London borough by area; substantial Green Belt; conservation areas in most town centres; generally permissive elsewhere. Read that before choosing a basement extension route in Bromley — construction, not postcode, sets what is achievable.

What happens if a Bromley property sits on a boundary?

• Croydon — adjoining Bromley, with 24 conservation areas centred on CR0. A basement extension on the far side of the Bromley line is determined by Croydon Council, so the Bromley quote for basement extensions is checked against Croydon guidance before it is issued.
• Southwark — adjoining Bromley, with 43 conservation areas centred on SE1. A basement extension on the far side of the Bromley line is determined by Southwark Council, so the Bromley quote for basement extensions is checked against Southwark guidance before it is issued.
• Lewisham — the Lewisham boundary runs against Bromley, so a basement extension a street from Bromley is decided by Lewisham Council instead. Lewisham runs 30 conservation areas across SE3 and its neighbours, which is why basement extensions priced for Bromley are re-checked against Lewisham policy whenever the Bromley address sits on that edge.
• Greenwich — cross the Bromley boundary and Greenwich Council takes the basement extension instead, applying 20 conservation areas of its own around SE3. We re-price basement extensions at the Bromley edge because Greenwich policy and Bromley policy rarely align on basement extension depth.

Sources for this Bromley 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.