Guide · 19 October 2026

Building costs and house prices in Bromley

Bromley is London’s largest borough by area, and its Local Plan says open countryside protected as Green Belt makes up more than half of it, with most residents living in the built-up northern part. The same document picks out tree-lined roads and houses with gardens as a distinctive feature of many of its residential areas. That shapes the work people can do. Compared with inner London there are fewer flat conversions and more houses with room beside or behind them, which is where side extensions, rooms over garages, lofts and large rear extensions come in.

The Census 2021 accommodation-type table (TS044, via Nomis) backs this up. Bromley had 135,827 households, and 18.1% of them lived in a detached house, the highest share of any London borough and three times the London figure of 6.1%. Another 29.9% lived in a semi (London: 18.6%) and 20.6% in a terrace. Only 23.5% lived in a purpose-built flat, against 40.3% across London, and 5.8% in a converted or shared house. In all, about 69% of Bromley households had a whole house to themselves.

Bromley house prices in July 2026

The most recent UK House Price Index from HM Land Registry and the ONS covers July 2026 (provisional), and gives Bromley an average price of £511,670. That is 3.1% down on July 2025, close to London’s fall of 3.3%, and 0.6% down on June. Bromley ranks 21st of London’s 33 local authority areas on average price, about £38,000 below the London average of £550,037. Prices have drifted lower for most of the past year and sit around 3% below the borough’s peak of £529,819 in December 2022. First-time buyers paid £391,216 on average.

Look along each row and every type of home in Bromley averages less than the London figure for the same type: roughly £100,000 less for a detached house, £71,000 less for a semi, £159,000 less for a terrace and £122,000 less for a flat. The overall average is only £38,000 below London’s partly because so many Bromley homes are houses rather than flats. Flats also fell furthest over the year. All of these figures come from the HPI full data file for July 2026; they are borough-wide averages that will be revised in later releases, and they can’t tell you what a particular house is worth.

Is it cheaper to move or to extend?

On July’s averages, stepping up from a terrace to a semi in Bromley cost about £169,000, and from a semi to a detached house about £414,000. Moving from a flat to a terrace added around £181,000. Those gaps leave out stamp duty, solicitors, surveys and removals, which all add to the cost of moving.

There are no published building costs for Bromley alone, so the figures below are national ballparks. Checkatrade’s house extension cost guide, last updated in June 2026 and checked by estimators who are members of RICS and the CIOB, gives these UK ranges excluding VAT:

• £1,800–£3,000 per m² for a finished single-storey extension, so £60,000–£84,000 for 30m²
• £45,000–£75,000 for a 25m² first-floor extension, for example over a garage
• £108,000–£180,000 for a 60m² two-storey extension
• £50,000–£95,000 for a 30m² loft conversion
• £100,000–£160,000 for a 40m² basement
• £8,500–£20,000 for a 15m² garage conversion

Checkatrade notes that its figures aren’t location-based and that builders in London and the South East usually charge more, so expect Bromley quotes to come in above them. Even allowing for that, a two-storey extension is a fraction of the £414,000 jump from a semi to a detached house. The terrace-to-semi gap of £169,000 is closer to what a big project could cost, but a loft or a single-storey rear extension still sits well below it. Building on doesn’t turn a semi into a detached house, and nobody can promise what the work will add when you sell, so use these numbers to check a budget rather than to predict a return.

Permitted development: what you can do without an application

Under the national rules explained on the Planning Portal, a single-storey rear extension can usually go 3 metres beyond the original back wall of a semi or terrace, or 4 metres for a detached house, without planning permission. The prior approval route raises those limits to 6 and 8 metres. A single-storey side extension can be up to 4 metres tall and up to half the width of the original house, and an extension of more than one storey can go back 3 metres if it stays at least 7 metres from the rear boundary. The loft conversion guidance allows up to 50 cubic metres of extra roof space on a detached or semi-detached house and 40 cubic metres on a terrace, as long as nothing projects beyond the front roof slope.

These rights don’t apply to flats and maisonettes, and they are cut back in conservation areas, where side extensions, rear extensions of more than one storey and roof extensions all need permission. Green Belt is not one of the designations that removes householder permitted development rights, but it matters a great deal once you need to apply, as the next section explains.

Bromley’s own rules: side space, design and the Green Belt

When an extension does need planning permission, Bromley judges it against its Local Plan, adopted in January 2019. Three policies come up again and again for householders:

• Policy 6, residential extensions: the scale, form and materials should respect the original house and the street, gaps between buildings should be kept where they add to an area’s character, and dormers should suit the roof and avoid prominent slopes unless dormers are already typical locally. The supporting text says flat-roofed side extensions of two or more storeys on houses with traditional roofs will normally be resisted unless well set back.
• Policy 8, side space: for anything of two or more storeys, the council will normally expect at least 1 metre between the building and the side boundary for its full height and length, and more where the street already has wider gaps. This is the policy that most often decides whether a first-floor extension over a side garage is possible, so measure the gap before you pay for drawings.
• Policy 51, Green Belt and Metropolitan Open Land: extensions to houses in these areas will only be permitted if the net increase in floor area is no more than 10% of the original house, measured externally. “Original” means the house as it stood on 1 July 1948, or as first built if later, so earlier extensions count against the allowance.

Even when work falls within permitted development, a Lawful Development Certificate from the council is useful evidence for a future buyer, and extensions and loft conversions still need building regulations approval.

Conservation areas, residential character areas and Article 4 directions

Bromley Council’s conservation areas page lists 47 conservation areas, from Chislehurst, Shortlands and Park Langley to village centres such as Downe, Cudham and Farnborough. The newest are Shortlands Village (2021) and The Covert and The Thrifts in Petts Wood (2022), and the national planning data service holds the same 47 council records. The council adopted new appraisals and management plans for five of them in June 2025.

Bromley also has a local designation that many buyers haven’t heard of: Areas of Special Residential Character. Policy 44 of the Local Plan names 13 of them, including Petts Wood, Park Langley, Bickley, Bromley Common, Chelsfield Park and The Knoll, and expects new development to respect their character. Several carry Article 4 directions that take away permitted development rights:

• Since 15 March 2022, directions covering most of these areas have removed the right to add storeys to a house, and to build new homes on top of existing buildings. In Petts Wood, the right to add storeys was removed earlier, by a direction confirmed in July 2021.
• Since 19 July 2022, a further direction for the Petts Wood Area of Special Residential Character has removed permitted development rights for roof enlargements and other roof alterations, so a dormer or hip-to-gable loft there needs planning permission. The Chislehurst Road Conservation Area in Petts Wood has lost the right to make other roof alterations.

Other directions cover individual conservation areas, such as Barnmead Road and Chancery Lane in Beckenham, Alexandra Cottages in Penge and The Chenies in Petts Wood, as well as some farmland and several protected views. Across the whole borough except the Biggin Hill and Darwin wards, a non-immediate HMO direction means turning a family house into a small house in multiple occupation needs permission; Biggin Hill and Darwin have their own immediate direction. The council’s list and the national Article 4 dataset both give the full set, so check the map for your own road before you commission drawings.

Basements and flood risk

The Planning Portal says a new basement is likely to need planning permission, and digging next to a neighbour’s foundations brings in the party wall process. In Bromley the bigger question is often water. The Local Plan explains that the borough sits in the catchments of the Ravensbourne and the Cray, both of which rise within Bromley. Defences and culverts have greatly reduced river flooding in the built-up areas, but surface water flooding is still a problem in places. Check the government flood map for planning for your address, and raise surface water with your designer before planning anything below ground.

Party walls

About half of Bromley households live in a semi or a terrace, so work on a shared wall is common. Steels into a party wall, a new wall on the boundary, or a foundation dug near a neighbour’s house can all need notice under the Party Wall etc. Act 1996. The excavation rules can apply to detached houses too: GOV.UK’s guidance covers a “3/6 metre notice” for digging near and below a neighbour’s foundations, as well as notices for party walls and new boundary walls, with example letters. If a neighbour disagrees, surveyors agree an award setting out how the work will be done. Talking to them before the paperwork arrives usually makes things easier.

Checking a builder

Treat cold callers with suspicion, especially anyone who turns up because they’ve seen scaffolding nearby, asks for a big cash deposit or gives a single round figure with no breakdown. A reliable firm will put the job in writing, link payments to stages of finished work, show proof of insurance and recent projects, and tell you who will sign off the building regulations, whether that is the council or a registered building control approver.

You can find registered tradespeople on TrustMark, work through Citizens Advice’s pre-work checklist, and report a rogue trader to your local Trading Standards office.

Figures change: get quotes before you decide

House prices here are UK HPI averages for July 2026; they are provisional and will be revised, and the August 2026 figures are due on 21 October 2026. Building costs are Checkatrade’s national figures, updated in June 2026, not Bromley quotes, and London work often costs more. Household figures are from Census 2021 (census day 21 March 2021). Planning details are taken from Bromley Council’s Local Plan and Article 4 pages as they stood when we checked them, and can change. Check the rules for your own address, and get at least three itemised quotes based on proper drawings before you decide whether to build or move.

Sources: UK House Price Index England: July 2026 (GOV.UK); UK HPI data downloads, July 2026 (full file, Bromley E09000006); ONS local house prices: Bromley; Census 2021 TS044 accommodation type (Nomis); Checkatrade: house extension costs; Planning Portal: extensions; Planning Portal: loft conversions; Planning Portal: basements; Bromley Local Plan (January 2019); Bromley Council: building control; Bromley Council: conservation areas; Bromley Council: Article 4 direction areas; Bromley Council: Article 4 directions on upward extensions; Bromley Council: Article 4 directions on roof alterations; Bromley Council: HMO Article 4 directions; Planning Data: Bromley conservation areas; Planning Data: Bromley Article 4 directions; GOV.UK flood map for planning; GOV.UK: Party Wall etc. Act guidance; TrustMark; Citizens Advice: before building work; GOV.UK: find local Trading Standards. Data checked 19 October 2026.