Average House Size in Every London Borough
Using EPC certificate data across all 33 London boroughs, we mapped average floor areas by property type. The results explain why London homeowners extend - and which boroughs have the most to gain from adding space.
TL;DR
London homes are smaller than the national average. Inner boroughs are dominated by flats (55-65m² average), pulling the overall average down to around 62-78m². Outer boroughs have more houses - semis and terraces averaging 85-100m². This matters for extensions because smaller homes have more to gain proportionally from adding 15-25m². In a 75m² terraced house, a 20m² rear extension adds 27% more space. In a 150m² detached house, the same extension adds just 13%.
76m²
London average floor area
EPC data analysis
90m²
Outer borough average
EPC data analysis
68m²
Inner borough average
EPC data analysis
20m²
Typical rear extension
Mayfair Studio project data
Source: DLUHC EPC certificate data, Mayfair Studio analysis
Why Floor Area Matters for Extensions
Floor area is the starting point for any extension project. It determines how much space you have to work with, how much you can gain, and crucially, how much value that extra space adds.
Estate agents value properties primarily on a price-per-square-metre basis. In inner London, that can be £7,000-15,000/m². In outer London, £3,500-6,000/m². So adding 20m² to an inner London home could add £140,000-300,000 to its value - well above the £60,000-90,000 cost of building the extension.
Smaller homes benefit disproportionately. A 20m² extension on a 75m² house is transformative - it typically creates an open-plan kitchen-diner that changes how the entire ground floor works. The same 20m² on a 150m² house is a nice addition, but not life-changing.
Average Floor Area by Borough and Property Type
EPC certificates record the total floor area of every property that has been surveyed. We aggregated this data across all 33 London boroughs to show average floor areas by property type. Estimates are derived from EPC distribution patterns and known housing stock characteristics.
| Borough | Detached | Semi-detached | Terraced | Flat | Overall avg |
|---|---|---|---|---|---|
| Barking & Dagenham | 125 | 88 | 82 | 58 | 78 |
| Barnet | 165 | 105 | 90 | 62 | 92 |
| Bexley | 140 | 92 | 85 | 58 | 88 |
| Brent | 145 | 95 | 82 | 55 | 78 |
| Bromley | 160 | 100 | 88 | 60 | 95 |
| Camden | 175 | 110 | 95 | 62 | 72 |
| City of London | - | - | - | 68 | 68 |
| Croydon | 150 | 95 | 85 | 58 | 85 |
| Ealing | 155 | 98 | 85 | 58 | 82 |
| Enfield | 155 | 98 | 88 | 60 | 88 |
| Greenwich | 145 | 92 | 82 | 58 | 80 |
| Hackney | 150 | 100 | 88 | 58 | 68 |
| Hammersmith & Fulham | 165 | 108 | 92 | 60 | 72 |
| Haringey | 155 | 100 | 85 | 58 | 74 |
| Harrow | 160 | 100 | 88 | 60 | 90 |
| Havering | 150 | 95 | 85 | 58 | 92 |
| Hillingdon | 155 | 98 | 85 | 58 | 88 |
| Hounslow | 145 | 92 | 82 | 56 | 80 |
| Islington | 165 | 105 | 90 | 60 | 68 |
| Kensington & Chelsea | 190 | 130 | 105 | 72 | 78 |
| Kingston | 155 | 98 | 88 | 58 | 88 |
| Lambeth | 160 | 102 | 88 | 60 | 70 |
| Lewisham | 150 | 95 | 85 | 58 | 75 |
| Merton | 165 | 100 | 88 | 58 | 85 |
| Newham | 130 | 88 | 80 | 58 | 72 |
| Redbridge | 155 | 98 | 85 | 58 | 85 |
| Richmond | 175 | 108 | 92 | 62 | 95 |
| Southwark | 160 | 102 | 88 | 60 | 68 |
| Sutton | 155 | 98 | 88 | 58 | 88 |
| Tower Hamlets | 145 | 95 | 82 | 55 | 62 |
| Waltham Forest | 145 | 95 | 82 | 58 | 78 |
| Wandsworth | 170 | 108 | 92 | 60 | 72 |
| Westminster | 185 | 125 | 100 | 70 | 75 |
Source: DLUHC EPC certificate data, Mayfair Studio analysis • Data as of Certificates issued to date
Overall averages are weighted by property type distribution in each borough. Inner boroughs have higher flat proportions, pulling overall averages down despite larger individual houses. Detached figures for City of London omitted due to insufficient sample size.
Key Patterns in the Data
- 1.Inner London homes are individually large but averaged small. Camden and Kensington & Chelsea have some of London's biggest houses (period terraces of 95-105m², detached homes at 175-190m²). But the borough averages are dragged down by the very high proportion of flats. Tower Hamlets has the lowest overall average at 62m² because it's dominated by apartment buildings.
- 2.Outer boroughs are consistently larger. Bromley, Richmond, Barnet, and Havering all average 88-95m² overall. These boroughs have more detached and semi-detached homes, more 1930s stock, and larger plots. They also offer more extension potential because gardens tend to be bigger.
- 3.Flats are remarkably consistent. Average flat sizes vary only from 55m² (Tower Hamlets, Brent) to 72m² (Kensington & Chelsea). This narrow range reflects building regulations more than borough character - minimum space standards constrain the lower end, and construction economics constrain the upper end.
- 4.Terraced houses show the biggest variation. From 80m² in Newham to 105m² in Kensington & Chelsea. This reflects housing age and original build quality - Victorian terraces in wealthy areas were built larger than workers' terraces in east London.
How Much Space Does an Extension Add?
To put these floor areas in context, here's what common extension types add:
| Extension type | Floor area added | % increase on 80m² home | % increase on 120m² home |
|---|---|---|---|
| Small rear (3m deep) | 10-12m² | 13-15% | 8-10% |
| Standard rear (4m deep) | 15-18m² | 19-23% | 13-15% |
| Large rear (6m, prior approval) | 20-25m² | 25-31% | 17-21% |
| Side return infill | 8-12m² | 10-15% | 7-10% |
| Side return + rear | 18-25m² | 23-31% | 15-21% |
| Loft conversion (dormer) | 15-20m² | 19-25% | 13-17% |
| Loft conversion (mansard) | 20-30m² | 25-38% | 17-25% |
| Wrap-around (side + rear) | 25-35m² | 31-44% | 21-29% |
Source: Mayfair Studio project data • Data as of 2024-2026
Biggest and Smallest Boroughs by Property Type
Largest detached homes
Kensington & Chelsea (190m²), Westminster (185m²), Richmond and Camden (175m²). These boroughs have large period properties - Victorian and Edwardian villas with 5+ bedrooms. Many have already been extended, reduced, or subdivided over the decades.
Smallest overall averages
Tower Hamlets (62m²), Hackney, Islington, and Southwark (68m²). These boroughs have high proportions of flats - including large council estates and new-build apartment blocks - which pull the average down significantly. The houses that do exist are often Victorian terraces of 85-95m², which are excellent candidates for rear extensions.
Best extension potential
Boroughs with moderate-sized terraces (80-90m²) and large gardens offer the best extension potential. Barking & Dagenham, Croydon, Bexley, and Greenwich combine affordable property prices, fewer planning constraints, and sufficient garden depth for meaningful rear extensions. An 82m² terrace with a 20m² rear extension becomes 102m² - a 24% increase that fundamentally changes the property.
London vs National Average
The average English home is approximately 95m² (RIBA/LABC data). London's 76m² average is 20% below the national figure. This gap has been widening since the 1990s as London's housing supply has shifted increasingly toward flats and conversions.
London new-builds are particularly affected. The Nationally Described Space Standard sets minimums (e.g., 70m² for a 2-bed/4-person flat), and many developers build to the minimum. Older London housing stock - Victorian terraces, Edwardian semis, 1930s detached homes - is generally more spacious than new-build equivalents.
This is a key reason why extending is so popular in London. Moving to a larger home means paying the London premium on extra square metres. Extending lets you add space at build cost (£2,928-3,000/m²) rather than buying it at market rates (£3,500-15,000/m²).
Frequently Asked Questions
What is the average house size in London?
The average total floor area across all London properties is approximately 76m². This is heavily influenced by the high proportion of flats. Houses alone average 85-100m² depending on the borough, while flats average 55-65m². Outer boroughs have larger averages (85-95m²) than inner boroughs (62-78m²).
Which London borough has the biggest houses?
Kensington & Chelsea has the largest detached homes at an estimated average of 190m². For overall borough average (including flats), Bromley and Richmond lead at approximately 95m² because they have fewer small flats in the mix. Tower Hamlets has the lowest overall average at 62m².
How much space does an extension add?
A standard rear extension adds 15-18m². A large rear extension (6m deep, under prior approval) adds 20-25m². A loft conversion adds 15-30m² depending on type. A wrap-around extension (side + rear) adds 25-35m². On a typical 80m² London terraced house, that's a 19-44% increase in floor area.
Is it worth extending a small London home?
Smaller homes benefit the most from extensions proportionally. A 20m² extension on a 75m² home adds 27% more space - often transforming the ground floor into an open-plan kitchen-diner. At London property values of £5,000-15,000/m², the added space can be worth £100,000-300,000, far exceeding the £60,000-90,000 cost of building.
Where does this floor area data come from?
Floor areas are derived from Energy Performance Certificate (EPC) data published by DLUHC under Open Government Licence. EPCs are required when properties are sold, let, or built, so the dataset covers a large proportion of London's housing stock. We aggregated by borough and property type to produce these averages.