Guide · 18 October 2026

Building costs and house prices in Brent

Brent is really two boroughs when it comes to homes. In the south-east, around Kilburn, Queens Park, Willesden and Kensal Rise, you find long Victorian and Edwardian streets, many of them split into flats decades ago. Further north and west, in places like Kingsbury, Kenton, Preston and Sudbury, the railway brought what the council’s heritage pages call suburban “Metroland” building between the wars: semis with bays, gables and front gardens that have often been paved for parking. What you can add to a house, and how hard the council will look at it, depends a lot on which of the two you live in.

The Census 2021 accommodation-type table (TS044, via Nomis) shows the mix. Of Brent’s 118,612 households, 22.3% lived in a semi-detached house, above the London figure of 18.6%. Only 14.9% lived in a terrace (London: 21.3%) and 6.0% in a detached house. Purpose-built flats housed 38.0%, and a further 16.5% lived in part of a converted or shared house, well above the London share of 11.1%. So fewer than half of Brent households, about 43%, have a whole house of their own to extend.

Brent house prices in July 2026

The latest UK House Price Index, for July 2026 (provisional) from HM Land Registry and the ONS, puts the average Brent home at £546,135. That is 2.6% lower than a year before, a slightly smaller fall than London’s 3.3%, and leaves Brent 16th of the 33 London local authority areas on price, close to the London average of £550,037. The borough’s average fell to £537,116 in February 2026, then edged back, with a 1.2% rise in July. It is still about 9% below the September 2022 high of £599,334. First-time buyers paid £473,234 on average in July.

The table shows an unusual pattern. Every kind of house costs more in Brent than the London average for that type, a semi by roughly £106,000, yet the average flat costs about £45,000 less, and flat prices have fallen fastest. The figures come from the HPI full data file for July 2026. They are borough-wide averages, mixing Kilburn conversions with Kingsbury semis, so they describe the market rather than value any one home, and the latest months are usually revised.

Moving up or building out?

On those averages, going from a terrace to a semi in Brent meant paying about £130,000 more in July 2026, and going from a semi to a detached house about £496,000 more. Moving from a flat to a terraced house added about £321,000. Any move also brings stamp duty, legal fees and removal costs on top.

No published source gives building costs for Brent itself, so the figures below are national. Checkatrade’s house extension cost guide (updated June 2026, figures checked by estimators who are RICS and CIOB members) gives UK ballparks, excluding VAT, of about:

• £1,800–£3,000 per m² for a finished extension, or £60,000–£84,000 for a 30m² single-storey one
• £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

The same guide says builders in London and the South East usually charge more than its figures, so treat them as a floor for Brent rather than a quote. Even so, the comparison is clear at the top end: a loft or a ground-floor extension on a semi costs a fraction of the near-£500,000 step up to a detached house. Between a terrace and a semi the margin is thinner, and a large two-storey project could cost about as much as the £130,000 price gap. An extension doesn’t change what type of house you own, and nobody can promise what it adds to a sale price, so use these sums to test a budget, not to forecast a profit.

What permitted development allows

Many house extensions need no planning application. The Planning Portal’s extension rules allow a single-storey rear extension of up to 3 metres beyond the original rear wall of a semi or terrace (4 metres for a detached house), or up to 6 and 8 metres through the prior approval process. A single-storey side extension can be up to 4 metres high and half the width of the original house. Extensions of more than one storey can go back 3 metres, but must stay at least 7 metres from the rear boundary. For lofts, the loft conversion rules allow up to 40 cubic metres of extra roof space on a terrace and 50 cubic metres on other houses, with nothing projecting beyond the front roof slope.

Two groups miss out. Flats and maisonettes have no householder permitted development rights, and Brent’s guidance says homes in a house converted into flats will normally need planning permission for most external changes. That covers a large share of the borough. In conservation areas, side extensions, rear extensions of more than one storey and loft additions all need permission, and the larger prior approval route isn’t available.

Brent’s own guidance on extensions

When an application is needed, Brent judges it against its Residential Extensions and Alterations SPD, adopted on 16 January 2025 to replace the 2018 version. The council says it will also apply this guidance to prior approval cases. Some of its main numbers:

• Single-storey rear: up to 6 metres deep on a terrace or semi and 8 metres on a detached house, but never more than half the length of the garden.
• Two-storey rear: no deeper than 3 metres (4 metres if detached), and kept within a 45-degree line taken from the nearest rear windows of the neighbours.
• Side extensions: no wider than two-thirds of the original house. At two storeys, the first floor and roof must be set back at least 0.5 metres from the front wall, and the roof should match the house.
• Roofs: rear dormers can run the full width of the original roof if set at least 0.2 metres up from the eaves, and a hipped roof can be converted to a gable if the result suits the street.

For a Metroland semi, that typically means a hip-to-gable loft with a rear dormer, a side extension that stops short of the full width, and a rear extension sized to your garden.

Basements and flood risk

Brent has a separate Basement SPD (adopted June 2017). It says a new basement should be no wider than the original house, should go no more than 3 metres beyond the back of the property and should be only one storey deep. It must also be reached from inside the house, because the council won’t accept a basement as a separate dwelling. Front lightwells, where allowed, are limited to 800mm or half the front garden’s depth, whichever is less. The document notes that parts of the borough flood from the River Brent and its tributaries, so check the government flood map for planning early. The Planning Portal says digging a new basement is likely to need planning permission, and on a terrace or semi it will usually bring in the party wall process too.

Conservation areas and Article 4 directions

Brent Council’s listed buildings and conservation areas page lists 22 conservation areas, from Mapesbury, Queens Park, Kensal Rise and Willesden Green in the south to Barn Hill, Northwick Circle, Sudbury Court and Roe Green Village further north. Its Article 4 page says all of the borough’s residential conservation areas are covered by Article 4 directions. The national planning data service still shows 23, because it includes Sudbury Cottages, which the council took off its list on 28 May 2024.

The directions can go further than people expect. Mapesbury’s non-immediate Article 4 direction, in force since 1 September 2025, brings almost every outside change under council control: extensions other than single-storey rear ones within the width of the house, roof alterations, porches, outbuildings, paving the front garden, chimneys, front walls and gates, most exterior painting, and solar panels anywhere but the rear roof slope. Non-immediate directions were also confirmed in 2025 for Brondesbury, Kensal Rise, Queens Park and Willesden Green. Check your own area’s direction and design guide before you get drawings done.

Away from conservation areas, a Article 4 direction on HMOs, in force since 1 November 2022, means you need planning permission to turn a family house into a small house in multiple occupation. It covers the whole borough apart from the Old Oak and Park Royal Development Corporation area and the growth areas listed in the notice. In that part of Park Royal, the development corporation rather than Brent is the planning authority. Even when work counts as permitted development, a Lawful Development Certificate from the council gives you proof for a future buyer, and building regulations approval is still needed for extensions and loft conversions.

Party walls

Semis share one wall and terraces share two, and Brent’s Victorian conversions often have neighbours above and below as well. Cutting steels into a shared wall, building on the boundary or digging foundations near a neighbour’s house usually means serving notice under the Party Wall etc. Act 1996. GOV.UK’s guidance gives the minimum notice: two months for work on a party wall, one month for a new wall on the line or for excavation nearby. If a neighbour dissents, surveyors draw up an award, so talking to them before the letters go out tends to save time and fees.

Checking a builder

Be wary of anyone who knocks on your door after spotting a skip or scaffold up the road, wants a large deposit in cash, has no fixed address or quotes a single price with no breakdown. A sound firm will give you a written contract with staged payments tied to finished work, show you insurance documents and recent jobs, and tell you whether council building control or a registered building control approver will sign off the work.

You can search for registered tradespeople on TrustMark, go through Citizens Advice’s checklist before work starts, and report a rogue trader to your local Trading Standards office.

Figures change: get quotes before you decide

Prices in this guide are UK HPI averages for July 2026, which are provisional and will be revised. Build costs are Checkatrade’s national figures as updated in June 2026, not Brent quotes, and London work often costs more. Household figures are from Census 2021 (21 March 2021). Planning details come from Brent Council documents current 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 commit to building or moving.

Sources: UK House Price Index England: July 2026 (GOV.UK); UK HPI data downloads, July 2026 (full file, Brent E09000005); ONS local house prices: Brent; Census 2021 TS044 accommodation type (Nomis); Checkatrade: house extension costs; Planning Portal: extensions; Planning Portal: loft conversions; Planning Portal: basements; Brent Council: Residential Extensions and Alterations SPD (2025); Brent Council: Basement SPD (2017); GOV.UK flood map for planning; Brent Council: listed buildings and conservation areas; Brent Council: Article 4 directions; Brent Council: Mapesbury non-immediate Article 4 direction; Brent Council: HMO Article 4 notice; Planning Data: Brent conservation areas; Planning Data: Brent Article 4 directions; GOV.UK: Party Wall etc. Act guidance; TrustMark; Citizens Advice: before building work; GOV.UK: find local Trading Standards. Data checked 18 October 2026.