Guide · 29 October 2026

Building costs and house prices in Hammersmith and Fulham

Hammersmith and Fulham is a long, narrow borough that runs from the canal at Old Oak down to the Thames at Fulham and Sands End, and most of its houses are Victorian and Edwardian terraces packed close together. Many of those terraces were split into flats long ago, so the person asking “should we extend?” here is often the owner of a whole house, while the neighbour through the wall owns one floor of one. Both questions are covered below, but they lead to very different answers.

The Census 2021 accommodation-type table (TS044, via Nomis) shows how unusual the mix is. Of 81,243 households, 48.1% lived in a purpose-built block of flats and 24.5% in a flat inside a converted or shared house. That second figure is more than double London’s 11.1%, and only Camden has a higher share. Terraced houses held 18.8% of households, semis 4.7% and detached houses just 1.1%, so about one household in four lives in a whole house, against 46% across London.

What homes cost in Hammersmith and Fulham in August 2026

The UK House Price Index from HM Land Registry and the ONS, published on 21 October 2026, puts the borough’s average price for August 2026 at £754,825. These figures are provisional. That is 5.1% lower than a year earlier, one of the steeper falls in London, although prices rose 1.6% on July. The London average was £554,430 (down 2.2%), so a typical home here costs about £200,000 more than the capital’s average and the borough ranks 5th of 33 on price. Prices peaked at £889,834 in March 2023 and are now about 15% below that. First-time buyers paid £643,534 on average, and buyers who had owned before paid £929,765.

The average terrace costs well over a million pounds, and only Kensington and Chelsea, Westminster and Camden have a dearer one. Flats took the biggest fall, which matters in a borough where most people live in one. The detached and semi figures need care: with so few of these houses, only a handful sell, and the HPI models these figures rather than averaging actual sales. Land Registry counted 107 sales of all types in the borough in June 2026, the latest month with a count. The figures come from the HPI full data file and the ONS local house prices page for Hammersmith and Fulham. They are borough-wide, will be revised, and can’t value any particular home.

Move to a bigger home, or build?

On August’s averages, going from a flat to a terraced house meant finding about £593,000 more, and going from a terrace to a semi about £372,000 more. The semi-to-detached step was about £219,000, though it rests on very few sales. Stamp duty, legal fees, surveys and removals sit on top of each gap, and at these prices stamp duty alone can be a five- or six-figure sum.

No one publishes building costs for this borough alone, so the costs below are national. Checkatrade’s house extension cost guide (updated June 2026, with estimates checked by RICS and CIOB members) gives these UK ranges, excluding VAT:

• £1,800–£3,000 per m² for a finished single-storey extension
• £30,000–£42,000 for a small (15m²) rear extension to a mid-terrace house
• £108,000–£180,000 for a two-storey extension of 60m²
• £50,000–£95,000 for a 30m² loft conversion
• £100,000–£160,000 for a 40m² basement
• £350–£950 for architectural drawings

Checkatrade says its figures aren’t based on location and that London and the South East usually cost more, so expect local quotes above these ranges, plus VAT. Even so, a side infill or a loft on a terrace here would normally cost a small fraction of the £372,000 needed to trade up to a semi. That sum is why so many owners stay and build. Flat owners face a harder choice. Flats have no permitted development rights, almost any work outside the flat’s own walls needs planning permission, and a leaseholder will usually need the freeholder’s written consent. For many, moving is the only practical way to gain much more space. Don’t count on getting the building cost back when you sell. Judge the work on whether it gives you the room you need.

Permitted development: the national starting point

For houses, the Planning Portal’s extension guidance sets out what can be built without applying. A single-storey rear extension can go 3 metres beyond the original back wall of a terrace or semi (4 metres for a detached house), or 6 and 8 metres under the prior approval scheme, where the council asks the neighbours first. A single-storey side extension can be up to 4 metres high and half the width of the original house. The loft conversion guidance allows up to 40 cubic metres of extra roof space on a terrace and 50 cubic metres on other houses, with nothing projecting from the roof slope that faces the road.

Two things narrow those rights here. Roughly half the borough is conservation area, where permitted development doesn’t cover side extensions, rear extensions of more than one storey or roof enlargements such as dormers. Many streets also have Article 4 directions that remove more rights (see below). If your plans do fit within permitted development, apply for a Lawful Development Certificate so a future buyer’s solicitor can see the work was lawful. Building regulations approval is needed whichever route you take.

How the council judges extensions

Applications are decided against the London Plan and the council’s Local Plan, adopted on 28 February 2018, which covers alterations and extensions in policy DC4. The detail sits in the Planning Guidance Supplementary Planning Document (SPD), also adopted in February 2018. A replacement Local Plan is on its way: the council’s Cabinet approved the version for formal consultation on 6 July 2026, and its Cabinet report plans submission to the government in December 2026 and an examination from March 2027. Until it is adopted, the 2018 plan and SPD apply. The SPD points most likely to affect a house extension are these:

• Rear extensions. Permission is not normally granted for an extension more than 3.5 metres long (counting any earlier extension) beyond the back addition as originally built, one that comes within 4 metres of the rear boundary, or one that, with earlier extensions, covers more than half of the original open space at the back. These are stricter in places than permitted development, and the council encourages owners to follow them even where no application is needed.
• Daylight to neighbours. The council uses a 45-degree line, drawn from ground level at the boundary where the neighbour’s garden is under 9 metres deep, and from 2 metres up where it is deeper. A new extension shouldn’t break that line.
• Side infills. Where an extension fills the gap beside a back addition, the wall on the boundary should be no more than 2 metres high, with the roof sloping away at no more than 45 degrees. New windows should normally be at least 18 metres from windows of habitable rooms opposite.
• Roofs in conservation areas. The SPD’s conservation guidance says front roof extensions are generally unacceptable, rear ones must be sympathetic and original chimneys should stay. Hip-to-gable conversions can upset the symmetry of a group or terrace, so where hipped roofs are part of the original pattern, losing them will be resisted.

Conservation areas and Article 4

The council lists 44 conservation areas covering about half of the borough, with two more around Old Oak managed by the Old Oak and Park Royal Development Corporation, which handles planning there. In a conservation area you need permission for more types of work, and the design has to respect the street.

Article 4 directions go further. The council’s Article 4 page lists directions covering parts of Bishops Park, Brook Green, Central Fulham, Hammersmith Grove, Hurlingham, Parsons Green, Ravenscourt and Starch Green, St Peter’s Square, Walham Grove and others. Depending on the direction, they can bring front windows and doors, porches, front walls, roof coverings, roof extensions at the front and even painting the outside under planning control. The council publishes a list of the properties affected, so check your address before you order windows or draw a roof.

Basements, groundwater and the Thames

The Planning Portal says a new basement is likely to need planning permission. Local Plan policy DC11 sets firm limits: no further into the garden than half the depth of the house or half the depth of the garden, set back from the neighbours’ boundaries, normally one storey only, and at least a metre of soil over any part beneath a garden. Every application needs a Construction Method Statement from a qualified structural or civil engineer, including a construction traffic plan, and lightwells at the front or side must be discreet.

Flooding is the bigger local issue. The Local Plan says over 60% of the borough lies in the Environment Agency’s Flood Zones 2 and 3, protected by the Thames defences, and the SPD says most of the southern half of the borough is at high risk of groundwater flooding. Self-contained basement flats are not allowed in Flood Zone 3 where a breach of the defences could flood them quickly, unless there is a safe way out. Check your address on the government flood map for planning and ask your designer about waterproofing and pumped drainage before going any further.

Party walls in a borough of terraces

With terraces and converted houses everywhere, almost any loft, rear extension or basement here touches the Party Wall etc. Act 1996. Putting steel beams into a shared wall, building on the boundary or digging near a neighbour’s foundations all mean serving notice, and in a house split into flats the neighbours can include the flats above and below you. GOV.UK’s party wall guidance explains the notices and time limits. If a neighbour disagrees, one agreed surveyor or one for each side draws up an award on how the work will be done, normally at the cost of whoever is building. A friendly conversation before the paperwork arrives tends to save time and money.

How to avoid a rogue builder

Be wary of anyone who knocks on the door offering work, pushes you to decide on the spot, asks for a large payment in cash before starting or quotes a single round number. A good builder gives you an itemised quote and a written contract, takes payment in stages as work is completed, shows you their insurance and past jobs, and tells you who will handle building regulations sign-off.

Look for registered firms through TrustMark, work through Citizens Advice’s checklist before building work, and report rogue traders to your local Trading Standards office.

Figures change: get quotes before you decide

House prices here are UK HPI figures for August 2026, published 21 October 2026. They are provisional and will be revised, and the September 2026 figures are due on 18 November 2026. Building costs are Checkatrade’s national ranges, last updated June 2026. They are not local prices, and work in London usually costs more. Household figures are from Census 2021, taken on 21 March 2021. Planning details come from the council’s 2018 Local Plan, its February 2018 SPD and its web pages as they stood when we checked them on 29 October 2026, and they will change once the new Local Plan is adopted. Check the rules for your own address, and get at least three itemised quotes based on proper drawings before choosing between building and moving.

Sources: UK House Price Index England: August 2026 (GOV.UK); UK HPI data downloads, August 2026 (full file, Hammersmith and Fulham E09000013); ONS local house prices: Hammersmith and Fulham; Census 2021 TS044 accommodation type (Nomis); Checkatrade: house extension costs; Planning Portal: extensions; Planning Portal: loft conversions; Planning Portal: basements; Hammersmith & Fulham Council: Local Plan; Local Plan 2018 (PDF); Planning Guidance SPD (February 2018); Cabinet report: Local Plan Regulation 19 (July 2026); Hammersmith & Fulham Council: conservation areas; Hammersmith & Fulham Council: Article 4 directions; Properties affected by Article 4 directions (PDF); 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 29 October 2026.