Budget
£36,500
- Basic single-storey footprint increase with standard glazing
- Straightforward finishes
House Extension Costs in South East England
Estimates derived from UK trade benchmark data and regional labour indices, updated May 2026. Methodology →
House Extension in South East England often tracks above the national midpoint: commuter-belt demand and busy trades both nudge prices up. These numbers grow out of our UK guide, with that regional picture baked in.
In South East England, commuter-belt demand and trade availability usually keep quotes above the UK midpoint. For the full UK-wide baseline, compare with House Extension Cost UK.
The South East is the UK's busiest extension market — commuter-belt families extending instead of paying stamp duty to move — and quotes reflect a seller's market for good builders. Permitted development covers more schemes than in London, but the South Downs National Park, the protected landscapes (Chilterns, Surrey Hills, Kent Downs and High Weald) and the Metropolitan Green Belt catch many village plots that look unconstrained on paper.
Ground conditions vary more than most owners expect: Wealden clay moves seasonally and regularly triggers deeper foundations or engineered solutions on trees-nearby plots, while chalk generally digs and drains well but can hide dissolution features that need investigation. A soil-aware local builder prices this on day one; a cheap quote that assumes standard strip foundations is the classic South East extension overrun.
Timing is a real cost lever in this region. The busiest builders quote high in spring when demand peaks and order books fill for the year; the same firms often sharpen prices for autumn and winter starts on schemes where the heavy external work can be sequenced early. It is also normal here for quotes to carry short validity periods, because busy firms reprice as their order books and materials costs move — ask how long a price holds before you compare offers.
Two ways to take action on extension costs
Pick the path that fits where you are — running early numbers, or pressure-testing a quote you've already got.
Typical South East England house extension budgets
Three planning tiers for house extension in South East England, with scope and a representative figure for each. Run your own numbers in the calculator for a tailored range.
Mid-rangeMost common
£67,000
- Kitchen-diner extension with rooflights
- Good insulation
- Moderate internal reconfiguration
Premium
£190,500
- Complex steelwork
- Premium glazing
- Bespoke joinery
Typical regional cost ranges
| Item | Cost Range |
|---|---|
| Single-storey rear (small, 15 m²) | £22,500 – £45,000 |
| Single-storey rear (medium, 25 m²) | £39,000 – £73,000 |
| Single-storey build (per m²) | £1,350 – £3,150 |
| Double-storey (25 m² total) | £50,500 – £78,500 |
| Double-storey (40 m² total) | £67,000 – £106,500 |
Indicative range: £1,350–£3,350 per m².
At the mid-range, house extension in South East England benchmarks around £56,000 — around 12% above the UK average. The same project benchmarks around 9% higher in London (£61,000). Next door, London comes in around £61,000 and South West England comes in around £52,500.
How house extension costs vary across South East England
South East England is not one price. Across the postcode areas we track, Slough quotes typically run 13% higher than Medway for the same spec — these are the benchmarks by area:
| Area | Postcodes | vs UK average | Typical mid-range | Budget–premium span |
|---|---|---|---|---|
| Slough | SL | +18% | £59,000 | £23,500–£141,500 |
| Guildford | GU | +16% | £58,000 | £23,000–£139,000 |
| Oxford | OX | +16% | £58,000 | £23,000–£139,000 |
| Crawley | RH | +14% | £57,000 | £23,000–£137,000 |
| Dartford | DA | +14% | £57,000 | £23,000–£137,000 |
| High Wycombe | HP | +14% | £57,000 | £23,000–£137,000 |
| Tunbridge Wells | TN | +10% | £55,000 | £22,000–£132,000 |
| Milton Keynes | MK | +8% | £54,000 | £21,500–£129,500 |
| Portsmouth | PO | +8% | £54,000 | £21,500–£129,500 |
| Southampton | SO | +8% | £54,000 | £21,500–£129,500 |
| Canterbury | CT | +4% | £52,000 | £21,000–£125,000 |
| Medway | ME | +4% | £52,000 | £21,000–£125,000 |
Plus 2 more postcode areas between these ends of the range. Run the calculator with your postcode for a range tuned to your area.
Mini extension cost calculator
Three quick inputs and we'll email you an indicative range. Run the full calculator for a postcode-adjusted estimate.
Checking a South East England house extension quote?
What a fair house extension quote should itemise doesn't change by region — only the prices do. The full checklist, red flags and scripts live in our UK guide, benchmarked against the South East England figures above:
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Other renovation costs in South East England
All South East England renovation costsFrequently asked questions
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