the South East cost guide

Extension costs in the South East (2026): local prices by area

Updated October 2026Prices include VAT and fees

Quick answerA 20m² single storey rear extension in the South East typically costs £59,500 to £71,000 including VAT. Prices run below London but above most of England, because builders here work in the London commuter belt and price against it, especially in Surrey, Berkshire and Oxfordshire.

Typical prices in the South East

the South East the South East, South Eastindex 1.13

Single storey rear extension20 m² (5m × 4m)£59,500 to £71,000£3,240/m²
Kitchen extension with bifolds24 m² (6m × 4m), mid spec£78,500 to £94,000£3,570/m²
Double storey rear extension40 m² over two floors£96,000 to £114,500£2,600/m²
Dormer loft conversion2 bedrooms + en-suite£53,500 to £65,000
Velux loft conversion2 rooms£38,500 to £46,500
Garage conversion15 m² single garage£22,000 to £26,000£1,590/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

Building in the South East

The South East covers very different markets, from Surrey villages to Medway towns and the south coast. What links them is the pull of London: trades who could work in the capital charge accordingly, and demand for extensions is strong because moving house is expensive. Our figures adjust area by area, so Guildford and Reading price higher than Portsmouth, Canterbury or Chatham. Detached and semi-detached houses with gardens are more common here than in London, so larger rear and wraparound extensions are popular.

What moves the price in the South East

Commuter belt pricing

Towns within easy reach of London, such as Guildford, Redhill, Reading and Slough, carry some of the capital's labour costs. Builders often split their time between London and the home counties and quote to match. Further from London, on the Kent and Hampshire coast, prices ease noticeably.

Larger plots, larger projects

More houses here have the space for big rear extensions, double storey additions and garage conversions. Larger footprints bring down the cost per square metre slightly, but they also mean bigger foundations, steelwork and glazing, so the total climbs quickly.

Ground conditions

Parts of the region sit on clay that shrinks and swells, particularly where there are mature trees nearby. Building control may ask for deeper foundations in these spots, which adds to groundwork costs. Chalk and sandy areas tend to be simpler to build on.

Planning and building control in the South East

English permitted development rules apply, so many single storey rear extensions can be built without a planning application, and the larger home extension prior approval route allows deeper extensions in some cases. Much of the region is green belt or within national landscapes and conservation areas, where rights are often reduced. All extensions need Building Regulations approval through the council or an approved inspector. Check with your district council before committing to a design.

Prices across the South East

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
RG1	Reading	£61,500 to £73,500	£55,000 to £67,000	1.16
GU1	Guildford	£63,500 to £76,000	£57,000 to £69,500	1.21
BN1	Brighton	£60,500 to £72,500	£54,500 to £66,500	1.15

Cost index for every postcode area in the South East

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	Index
BN	Brighton	1.15
CT	Canterbury	1.07
DA	Dartford	1.14
GU	Guildford	1.21
ME	Medway	1.07
MK	Milton Keynes	1.10
OX	Oxford	1.18
PO	Portsmouth	1.10
RG	Reading	1.16
RH	Redhill	1.19
SL	Slough	1.18
SO	Southampton	1.12
TN	Tonbridge	1.15

the South East: common questions

How much does an extension cost in the South East?

A 20m² single storey rear extension in the South East typically costs £59,500 to £71,000 including VAT. A larger 24m² kitchen extension with bifolds and a roof lantern is usually around £78,500 to £94,000. Surrey and Berkshire price at the top of the region, coastal Kent and Hampshire lower.

Is a double storey extension worth it in the South East?

Often, because house prices are high and adding a bedroom adds real value. A double storey rear extension with 40m² over two floors typically costs £96,000 to £114,500 including VAT, which works out cheaper per square metre than building two single storey spaces.

Does green belt stop me extending?

Not usually, but it limits how much you can add. Green belt policy tends to restrict extensions that are disproportionate to the original house, so councils look at the total added over time. A planning consultant or the council's pre-application service can tell you what is likely to be accepted.

How long does an extension take in the South East?

Plan for around two months of drawings and approvals, then 10 to 16 weeks on site for a single storey extension. Good builders in the commuter belt are often booked several months ahead, so start conversations early.