Guide · 17 October 2026

Building costs and house prices in Bexley

Bexley is semi-detached country. Drive through Welling, Bexleyheath or Sidcup and you pass street after street of 1930s semis with bay windows, hipped roofs and a driveway down the side, many of them already carrying a loft dormer or a converted garage. Those houses were built with room to grow, which is why so many owners here weigh up adding a bedroom against moving a few roads over for one.

The figures back up the first impression. In the Census 2021 accommodation-type table (ONS TS044), 44.2% of Bexley’s 95,298 households lived in a semi-detached house. That is the highest share of any London borough and more than double the London-wide figure of 18.6%. Another 23.6% lived in a terrace and 7.4% in a detached house, so about three households in four live in a house rather than a flat. Purpose-built flats made up 21.3%.

What homes cost in Bexley now

The UK House Price Index for July 2026 (provisional), compiled by HM Land Registry with the ONS, puts Bexley’s average price at £413,343, up 2.0% on a year earlier. That runs against the London trend: the capital’s average was £550,037 and down 3.3% over the same year. Bexley came 30th of the 33 London local authority areas on price that month, making it the fourth cheapest.

The past year has been fairly flat. The borough average was £405,286 in July 2025, peaked at £415,780 in November, dipped to £402,720 in February 2026 and then rose again, with a 1.7% jump in July alone. First-time buyers paid an average of £361,301 in July 2026.

These averages come from the HPI full data file for July 2026. They cover the whole borough, from riverside flats in Erith to large houses near Old Bexley, so treat them as a picture of the market rather than a valuation of your home. Recent months are provisional and usually get revised.

Is it cheaper to buy the space or build it?

In July 2026 an average Bexley semi cost about £118,000 more than an average terrace, and an average detached house about £202,000 more than a semi. Stepping up from a flat to a terraced house added about £171,000.

For build costs there is no Bexley-specific published figure, so we use national ones. Checkatrade’s house extension cost guide, checked by estimators who are RICS and CIOB members and last updated in June 2026, gives these UK-wide ballparks, excluding VAT:

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

Checkatrade notes that builders in London and the South East usually charge more than these national figures, so expect a Bexley quote toward the upper end of each range, or above it.

Here the sums are closer than in pricier boroughs. A 60m² two-storey side extension on a semi could cost about as much as the £118,000 gap between a terrace and a semi, or more, so for someone in a terrace, moving up may cost no more than building. For a family already in a semi, the next step is a detached house at roughly £202,000 more, plus stamp duty, legal fees and removals, and there a loft, a garage conversion or a rear extension usually costs much less. Bear in mind that an extension doesn’t turn a semi into a detached house in a buyer’s eyes, and the value it adds when you sell isn’t guaranteed. Use these numbers to check a budget, not to predict a sale price.

What Bexley’s houses lend themselves to

Lofts in hipped roofs. A hip-to-gable conversion with a rear dormer is the standard upgrade for a 1930s semi. Under permitted development, you can add up to 50 cubic metres of roof space to a semi or detached house (40 cubic metres for a terrace) without a planning application, provided nothing extends beyond the front roof slope and the house isn’t in a conservation area.

Garage conversions. Many houses here have an attached or side garage. The Planning Portal’s garage conversion guidance says planning permission isn’t usually needed if the work is internal and doesn’t enlarge the building. Some estates had those rights removed by a planning condition, though, so check your property’s planning history first. Building regulations approval is still required.

Side and two-storey extensions. A side driveway leaves room for a single-storey side extension or a two-storey side addition. Under permitted development a single-storey side extension can be up to 4 metres high and half the width of the original house. Anything more than one storey at the side needs full planning permission.

Rear extensions. Without a full application, a single-storey rear extension can usually go 3 metres beyond the original back wall of a semi or terrace (4 metres on a detached house), or up to 6 and 8 metres under the prior approval route. The Planning Portal’s extension rules list the other limits, including the 50% plot coverage cap and the 7-metre rear boundary rule for two-storey rear extensions.

Basements. With gardens and lofts to use instead, digging down is uncommon in Bexley. If you’re thinking about it, read the Planning Portal basement guidance and allow for structural engineers, waterproofing and party wall costs on top of the build. Homes in the north of the borough near the Thames, or close to the River Cray or the Shuttle, should also check the government flood map for planning before planning any ground-floor or below-ground rooms.

Conservation areas and Article 4 in Bexley

The council’s conservation and heritage page lists 23 conservation areas, along with over 150 listed buildings and around 400 locally listed ones. The conservation areas range from Old Bexley and North Cray Village to Christ Church, The Green and The Oval in Sidcup, Lesney Park Road in Erith, Red House Lane in Bexleyheath and Woolwich Road in Upper Belvedere. In any of them, loft rights under permitted development don’t apply, side extensions need permission, and you should expect closer scrutiny of materials and windows.

Four conservation areas also have Article 4(2) directions that bring smaller changes under council control: Brook Street, Old Bexley, Old Forge Way and Red House Lane. The Article 4 directions page links to each one. In Old Forge Way, for example, the direction covers attic rooms, window changes, rendering and roof alterations. The same page lists a borough-wide Article 4 direction, in force since 24 September 2017, which means turning a family house into a small HMO (house in multiple occupation) needs planning permission.

If your plans do fit permitted development, it’s still worth applying to the council for a Lawful Development Certificate, because a buyer’s solicitor will ask for proof later. Building regulations approval is needed for extensions and loft conversions whatever the planning position.

Party walls

Almost every semi and terrace in Bexley shares a wall with the house next door, and a loft conversion usually means putting steels into it. That, building on the boundary, or digging foundations close to a neighbour’s house generally means serving notice under the Party Wall etc. Act 1996. GOV.UK’s party wall guidance sets out the notice periods: at least two months for work on the party wall itself and one month for excavation or a new wall on the boundary. A conversation over the fence before the paperwork arrives often avoids each side appointing its own surveyor.

How to avoid a rogue builder

Loft and extension work on suburban semis attracts doorstep traders. Walk away from anyone who turns up uninvited with a special offer, asks for a large cash deposit, has no fixed business address, or gives a single figure without breaking it down against drawings. A reputable builder will show you recent jobs nearby, put the price and stage payments in a written contract, prove their insurance, and tell you who is signing off building control.

You can look up registered firms on TrustMark, the government-endorsed quality scheme, work through Citizens Advice’s checklist before anyone starts, and report a problem trader to Trading Standards.

Figures change: get quotes before you decide

House prices here are UK HPI averages for July 2026, which are provisional and will be revised. Build costs are Checkatrade’s national ballpark figures as updated in June 2026, not Bexley quotes, and London work often costs more. Household figures are from Census 2021 (21 March 2021). Conservation area and Article 4 details come from Bexley Council and can change. Check the rules for your own address, and get at least three itemised quotes against proper drawings before you commit.

Sources: UK House Price Index England: July 2026 (GOV.UK); UK HPI data downloads, July 2026 (full file, Bexley E09000004); ONS local house prices: Bexley; Census 2021 TS044 accommodation type (ONS); Checkatrade: house extension costs; Planning Portal: loft conversions; Planning Portal: garage conversions; Planning Portal: extensions; Planning Portal: basements; GOV.UK flood map for planning; Bexley Council: conservation and heritage; Bexley Council: Article 4 directions; Planning Data: Bexley conservation areas; GOV.UK: Party Wall etc. Act guidance; TrustMark; Citizens Advice: before building work. Data checked 17 October 2026.