Building Costs in the South East 2026: Regional Price Guide
How much does building work cost in South East England in 2026? Extensions from £32,000 to £145,000, with county-level breakdowns and trade-by-trade detail.
The South East of England sits in an awkward pricing sweet spot - not quite London money, but well above the national average. If you're planning building work in Kent, Surrey, Sussex, Hampshire, Berkshire, Buckinghamshire, Oxfordshire, or Hertfordshire, you need South East numbers, not UK-wide averages.
In 2026, a single-storey rear extension in the South East costs £2,200–£3,800 per square metre (m²) - compared to a national average of £2,000–£3,300/m². For a typical 4m × 5m (20m²) extension with standard finishes, that's £44,000–£76,000 all-in. Not as steep as London, but enough to make the difference between a project that works financially and one that doesn't.
Quick cost summary
For South East England (excluding Greater London):
Extensions
| Size | Budget spec | Standard spec | High spec |
|---|---|---|---|
| 3m × 4m (12m²) | £32,000–£38,000 | £38,000–£46,000 | £50,000–£64,000 |
| 4m × 5m (20m²) | £44,000–£56,000 | £58,000–£76,000 | £78,000–£100,000 |
| 5m × 6m (30m²) | £66,000–£82,000 | £82,000–£105,000 | £108,000–£145,000 |
Other common projects
| Project | Budget | Standard | High spec |
|---|---|---|---|
| Loft conversion (dormer) | £38,000–£50,000 | £50,000–£64,000 | £64,000–£80,000 |
| Kitchen refurbishment | £12,000–£18,000 | £18,000–£30,000 | £30,000–£55,000 |
| Bathroom renovation | £6,000–£9,000 | £9,000–£15,000 | £15,000–£28,000 |
| New build garage | £18,000–£25,000 | £25,000–£35,000 | £35,000–£50,000 |
These are all-in costs including labour, materials, and VAT. They don't include professional fees (architect, structural engineer) or planning application costs.
Costs based on BCIS regional benchmarks (South East England) and MyBuildAlly quote analysis, Q1 2026. Your actual costs will vary based on specification, access, and local labour rates.
How the South East compares
The South East commands a ×1.05–1.15 multiplier over the national average. That's the second-highest region in the UK, behind only London.
| Region | Factor vs national avg |
|---|---|
| Greater London | ×1.15–1.30 |
| South East | ×1.05–1.15 |
| South West | ×0.95–1.05 |
| Midlands | ×0.90–1.00 |
| North West | ×0.85–0.95 |
| North East | ×0.80–0.90 |
But it's not the same everywhere. There's a gradient from the edges of London outward:
| Area | Typical premium | Why |
|---|---|---|
| Surrey (Guildford, Woking, Reigate) | ×1.12–1.18 | Proximity to London, very high property values |
| Hertfordshire (St Albans, Watford) | ×1.10–1.15 | Strong London commuter demand |
| Berkshire (Reading, Windsor) | ×1.08–1.14 | High property values, affluent demographic |
| Kent (Sevenoaks, Tunbridge Wells) | ×1.06–1.12 | Commuter belt, pockets of very high values |
| Buckinghamshire (Beaconsfield, Amersham) | ×1.10–1.16 | Chilterns AONB (protected landscape), expensive postcodes |
| Hampshire (Winchester, Farnham) | ×1.04–1.10 | Further from London, moderating influence |
| Sussex (Brighton, Chichester) | ×1.04–1.10 | Coastal premium in some areas, lower inland |
| Oxfordshire (Oxford, Henley) | ×1.06–1.12 | University city premium, Chilterns proximity |
Why the South East costs more
Three things push South East prices above the national average:
Labour drain to London. Skilled tradespeople can earn 25–35% more working in London. Many South East builders lose their best workers to London-rate contracts, which means fewer are available locally - and that pushes day rates up.
High demand, limited supply. The South East has some of the UK's highest property values, so more homeowners can justify - and afford - extension projects. Builders are busy, lead times are long (3–6 months is typical for a good one), and there's less pressure to compete on price.
Property values justify the spend. A £60,000 extension that adds £80,000 of value makes financial sense. In the South East, the value-add from extra space is higher than the national average, so homeowners are more willing to invest - and builders price accordingly.
Trade-by-trade breakdown for the South East
Groundworks and foundations - 15–20%
Ground conditions across the South East are mixed. The chalk downs of Kent and Sussex generally provide solid ground to build on, but clay pockets (especially in the Weald and parts of Surrey) need deeper foundations - which means more digging and a bigger bill.
| Foundation type | Cost per linear metre | When it's needed |
|---|---|---|
| Strip foundation (concrete trenches dug along your walls) | £150–£240 | Chalk or gravel subsoil, no trees nearby |
| Deep strip | £220–£360 | Clay soil, tree influence |
| Piled foundation (deep concrete columns drilled into the ground) | £350–£600 | Very poor or soft ground, significant tree proximity |
If you're building on clay in Surrey or the western Weald, expect foundations at the deeper (and pricier) end. On chalk in the North or South Downs, standard strip foundations are usually fine.
Budget: £4,500–£12,000 for a 20m² extension.
Structural shell - 25–30%
The structural costs in the South East are broadly in line with the national average - it's the same bricks, blocks, and steel. The premium comes from labour rates for bricklayers and roofers, which sit 8–15% above national averages.
Large glazing elements - bi-fold doors (the large folding glass doors that open up the back of your house), sliding doors, structural glass - are popular in the South East, where garden views tend to be a selling point. A 4m bi-fold run costs £4,000–£8,000 depending on the system. For a full breakdown of extension costs by component, see our kitchen extension cost guide.
Budget: £12,000–£28,000 for a 20m² extension.
First fix - 15–18%
First fix is the plumbing, electrics, and plastering that happen before your kitchen or bathroom goes in. The South East sits roughly 10% above the national average for these trades.
| Trade | National day rate | South East day rate |
|---|---|---|
| Electrician | £200–£300 | £230–£340 |
| Plumber | £200–£300 | £220–£330 |
| Plasterer | £180–£260 | £200–£290 |
Underfloor heating is increasingly popular in the South East - at £55–£80/m² for wet systems, it's a modest add at first fix stage. If your extension includes new plumbing, our guide on what to check in a plumber's quote covers the key line items and red flags.
Budget: £7,000–£14,000 for a 20m² extension.
Fit-out - 20–30%
This is where your choices really drive the total cost. The structural shell of a budget extension and a premium one differ by maybe 15%. The fit-out can differ by 300%.
| Component | Budget | Mid-range | Premium |
|---|---|---|---|
| Kitchen units (supply only) | £3,000–£5,500 | £6,000–£13,000 | £16,000–£32,000+ |
| Worktops | £500–£1,400 | £1,800–£3,500 | £4,000–£9,000 |
| Appliances | £1,800–£3,200 | £3,500–£6,500 | £7,000–£16,000+ |
| Flooring (per m²) | £25–£50 | £50–£100 | £100–£220 |
Second fix and decoration - 10–15%
Second fix is the finishing touches - final connections for sockets, switches, and taps, plus tiling, painting, and snagging (the walkthrough where you spot anything that needs fixing). Allow £3,500–£6,000 for a standard 20m² extension in the South East.
Planning and building regulations in the South East
Permitted development
Permitted development is your automatic right to make certain changes without applying for planning permission. The standard rules apply across the South East:
- Single-storey rear: Up to 3m depth (attached) or 4m (detached)
- Height limit: 4m maximum (3m within 2m of a boundary)
- Garden coverage: Extensions plus outbuildings can't cover more than 50% of the original garden
- Materials: Must match or be sympathetic to the existing house
Where the South East gets restrictive
Green Belt. Large areas of the South East fall within the Metropolitan Green Belt - the ring of protected land around London. Green Belt status doesn't prevent extensions outright, but it limits what you can do. Extensions mustn't be too large relative to the original building (the official term is "disproportionate additions"). In practice, this means planning officers look more carefully at size and design - and what counts as "too large" varies between councils, so check yours early.
Areas of Outstanding Natural Beauty (AONBs). An AONB is a protected landscape where planning rules are tighter. The South East has several major ones:
- Surrey Hills - covers a significant chunk of Surrey
- Kent Downs - runs from the M25 to the coast near Dover
- Chilterns - stretches into Buckinghamshire, Hertfordshire, and Oxfordshire
- High Weald - spans Kent, Sussex, and Surrey
- South Downs National Park - the entire ridge from Winchester to Eastbourne
In AONBs and national parks, permitted development rights are more restricted. Dormer loft conversions (the box-shaped extensions you see poking out of roofs), cladding changes, and outbuildings over a certain size all need planning permission.
Conservation areas. A conservation area is a protected zone where the council controls what you can change about your property's appearance. Market towns across the South East - Tunbridge Wells, Henley, Chichester, Farnham, St Albans - have extensive conservation areas. Side extensions, front alterations, and demolition within conservation areas typically need planning consent.
Planning application costs
| Item | Cost |
|---|---|
| Householder planning application | £258 |
| Architectural drawings | £1,200–£3,500 |
| Structural engineer | £400–£1,200 |
| Bat survey (if re-roofing or in rural area) | £300–£600 |
| Tree survey (if protected trees affected) | £350–£700 |
| Design and access statement | Usually included in architect fees |
Building regulations approval (the council inspection that makes sure your build meets safety standards) is mandatory for any extension: budget £500–£1,000. For a full walkthrough of the planning process and what counts as permitted development, see our planning permission guide for 2026.
Finding a builder in the South East
The South East has a healthy pool of building contractors, but the best are typically booked 3–5 months ahead. Starting your search early gives you better options and more competitive pricing.
Get at least three fixed-price quotes. Not estimates, not ballpark figures - detailed written quotes with a clear scope of works. If you're not sure what should be in a quote, read our guide on what a builder's quote should include.
Check their patch. Builders who work locally know the local planning authority, have established relationships with building inspectors, and understand the ground conditions. A builder from three counties away might be cheaper on paper but slower in practice.
Verify credentials. Federation of Master Builders membership, NICEIC (the national register of approved electricians) registration for electrical work, Gas Safe (the official register of qualified gas engineers) for any gas installations, and public liability insurance of at least £2 million. Once work begins, use our guide on how to check your builder's work to know what to inspect at each stage.
Use MyBuildAlly's free cost calculator to get a baseline before comparing quotes. If you know that a 20m² extension in your postcode should cost £58,000–£76,000, you can immediately spot a builder who's coming in at £42,000 (what's missing from the scope?) or £95,000 (are they pricing you out because they're too busy?).
What to watch for in the South East
The London overflow effect
Some South East builders charge London rates even though their overheads are lower. This happens most in Surrey, north Kent, and south Hertfordshire - the areas closest to London where builders can argue they're turning down London work to take yours.
Compare quotes carefully. A builder in Guildford quoting the same per-m² rate as one in Wandsworth is probably overcharging - their skip hire, parking, and access costs are genuinely lower.
Rural access issues
Countryside properties in the Weald, Chilterns, and Downs can have narrow lanes, weight-restricted bridges, and limited turning space. Ready-mix concrete lorries need a minimum 3.5m lane width and solid ground to park on. If your access is tight, expect surcharges for smaller deliveries or pump-truck hire (£400–£800 per visit) - and those visits add up quickly on a full build.
Protected species
If you're building in a rural area or near woodland, ecological surveys may be needed before planning permission is granted. Bat surveys (£300–£600) are the most common, but great crested newt and badger surveys can also be required. Here's the catch: these are seasonal - bat surveys can only be done May to September. Miss the window and you could be waiting six months before you can even apply for planning. Check early.
Flint and local materials
In parts of Kent, Sussex, and Hampshire, planning authorities may require you to use local materials - particularly flint facing (the knapped stone you see on older houses in these areas). Flint work is a specialist skill, and flint-faced walls cost 40–60% more than standard brick. If your house has flint elevations and the extension is visible from a public road, budget accordingly - and make sure your builder has actually done flint work before.
Septic tanks and drainage
Properties not connected to mains drainage (more common in the rural South East than you'd think) will need their septic system reviewed if you're adding bathrooms or increasing the household capacity. Upgrading a septic tank to a modern treatment plant runs £5,000–£10,000 - and you'll need to factor it into your budget from the start, not discover it halfway through the build.
How does this compare to London?
The South East offers genuine savings over London - typically 10–20% less for comparable work. You avoid congestion charges, skip permits are cheaper (or free), site access is usually easier, and party wall issues (the legal process you go through when building near a shared wall with your neighbour) are less frequent.
For a direct comparison with London prices, see our London extension cost guide. If you're weighing up whether to move further out or extend your current South East home, the cost differential matters.
Is your quote fair for the South East?
Three quotes for the same project in the South East can easily span a £15,000–£25,000 range. Some variation is normal - it reflects different labour rates, material choices, subcontractor relationships, and how busy the builder is.
The question isn't just whether the price is high or low. It's whether the scope is complete, the spec is clear, and the price is fair for what's included. That's where MyBuildAlly helps. Upload your builder's quote and we'll benchmark it against South East data, flag missing items, and highlight anything that looks off.
Sources
- BCIS Average Building Prices - regional cost benchmarks for South East England, Q1 2026
- Spon's Architects' and Builders' Price Book 2026 - material and labour rate reference
- Planning Portal - permitted development rules, Green Belt, and AONB restrictions
- FMB (Federation of Master Builders) - trade accreditation standards
- Analysis of residential construction quotes submitted to MyBuildAlly, January–March 2026