London cost guide

Extension costs in London (2026): real prices by postcode

Updated October 2026Prices include VAT and fees

Quick answerA 20m² single storey rear extension in London typically costs £71,000 to £88,500 including VAT, with inner postcodes at the top of that range. London sits well above the rest of the UK because labour rates are higher, sites are tight, and parking, skips and deliveries all cost more and take longer.

Typical prices in inner London

London London, Inner Londonindex 1.38

Single storey rear extension20 m² (5m × 4m)£71,000 to £88,500£3,940/m²
Kitchen extension with bifolds24 m² (6m × 4m), mid spec£93,000 to £115,500£4,310/m²
Double storey rear extension40 m² over two floors£114,500 to £142,500£3,180/m²
Dormer loft conversion2 bedrooms + en-suite£63,500 to £81,000
Velux loft conversion2 rooms£45,500 to £58,000
Garage conversion15 m² single garage£26,000 to £32,500£1,940/m²

All prices include 20% VAT, professional fees and statutory planning fees. Kitchen extension includes a mid-range kitchen, bifolds and a roof lantern.

Price my exact project

Typical prices in outer London

outer London Outer London, Outer Londonindex 1.24

Single storey rear extension20 m² (5m × 4m)£64,000 to £79,500£3,550/m²
Kitchen extension with bifolds24 m² (6m × 4m), mid spec£84,000 to £104,500£3,890/m²
Double storey rear extension40 m² over two floors£103,000 to £128,000£2,860/m²
Dormer loft conversion2 bedrooms + en-suite£57,500 to £72,500
Velux loft conversion2 rooms£41,000 to £52,000
Garage conversion15 m² single garage£23,500 to £29,500£1,740/m²

All prices include 20% VAT, professional fees and statutory planning fees. Kitchen extension includes a mid-range kitchen, bifolds and a roof lantern.

Building in London

London has the widest spread of building costs in the UK. A side return on a Victorian terrace in Walthamstow and a basement-level kitchen extension in Fulham can both be called an extension, but they are priced very differently. Our London figures split the capital into inner and outer postcode areas, then adjust again for the pockets where builders consistently charge more. Most London projects are on terraced or semi-detached houses with shared walls, so party wall costs and neighbour notice periods are part of the budget far more often than elsewhere.

What moves the price in London

Access and logistics

Many London jobs have no side access, so every block, bag of plaster and barrow of spoil goes through the house. Controlled parking zones mean paying for bay suspensions and skip licences from the borough, and some streets only allow deliveries at set times. All of this adds labour days that a suburban job outside London simply doesn't have.

Shared walls and neighbours

Terraces and semis make up most of London's housing, so a rear or side return extension usually touches a party wall. That often means a party wall surveyor for each neighbour, plus foundations designed around next door's footings. Budget time for the notice period before work starts, not just the surveyor's fee.

Labour market

Trades in London charge more per day, and good builders are often booked months ahead. Higher overheads for vans, parking, congestion charges and insurance feed into every quote. The effect is strongest in central and west London postcodes and eases towards the outer boroughs.

Planning and building control in London

London follows the same English rules as the rest of the country: many single storey rear extensions can go ahead under permitted development, and all extensions need Building Regulations approval. The difference is how often those rights are restricted. Large parts of inner London sit in conservation areas, and many boroughs use Article 4 directions to remove permitted development rights, especially for roof alterations and front changes. Check your borough's planning pages before assuming you can build without an application.

Prices across London

A 20m² single storey rear extension and a two-bedroom dormer loft with an en-suite, priced for each example postcode. All figures include VAT and fees.

Postcode	Area	Single storey, 20m²	Dormer loft	Index
N1	North London	£71,000 to £88,500	£63,500 to £81,000	1.38
SW11	South West London	£74,500 to £93,000	£67,000 to £85,000	1.45
BR1	Bromley	£64,000 to £79,500	£57,500 to £72,500	1.24

Cost index for every postcode area in London

Our index against the West Midlands base of 1.00. Higher means dearer. Enter a full postcode in the checker for district-level detail where we have it.

Area	Main town	Zone	Index
E	East London	Inner London	1.34
EC	Central London (City)	Inner London	1.49
N	North London	Inner London	1.38
NW	North West London	Inner London	1.42
SE	South East London	Inner London	1.34
SW	South West London	Inner London	1.45
W	West London	Inner London	1.46
WC	Central London (West End)	Inner London	1.49
BR	Bromley	Outer London	1.24
CR	Croydon	Outer London	1.20
EN	Enfield	Outer London	1.23
HA	Harrow	Outer London	1.26
IG	Ilford	Outer London	1.20
KT	Kingston upon Thames	Outer London	1.30
RM	Romford	Outer London	1.18
SM	Sutton	Outer London	1.23
TW	Twickenham	Outer London	1.30
UB	Southall and Uxbridge	Outer London	1.20

London: common questions

How much does a single storey extension cost in London?

A 20m² single storey rear extension in London typically costs £71,000 to £88,500 including VAT, or roughly £3,940 per square metre. Inner London postcodes such as SW, W and NW sit at the higher end, outer boroughs such as Bromley, Croydon and Romford lower down.

How much is a loft conversion in London?

A dormer loft conversion with two bedrooms and an en-suite typically costs £63,500 to £81,000 including VAT in London. A simpler Velux conversion with two rooms is around £45,500 to £58,000. Mansard conversions, common on London terraces where the council allows them, cost more because the whole rear roof slope is rebuilt.

Do I need planning permission for an extension in London?

Not always. Many single storey rear extensions qualify as permitted development, but conservation areas and Article 4 directions are common in London and can remove those rights. Your borough council's planning team, or a lawful development certificate, will confirm what applies to your house.

Why does an extension in London cost so much more than in the Midlands?

The materials are similar, but labour, access and logistics are not. London builders pay more for staff, parking and insurance, and tight terraced sites take longer to work on. Party wall costs are also more common because most houses share at least one wall.