House Extension Cost UK 2026: Real Prices, Every Zone, Every Level
A cheap quote is not always a fair quote. Before you sign anything, know what a genuine extension actually costs — labour, materials, compliance and VAT included, nothing hidden.
Types of Extension Covered on This Page
- Rear extension — single storey
- Rear extension — double storey
- Side return extension
- Wrap-around extension
- Garage conversion
- Outbuilding / garden room
All prices below are calculated per square metre (£/m²), because extension cost scales with floor area, not with a fixed “average UK price” that ignores your actual project size.
Four Price Levels, Four Sub-Levels Each
Every price band below has four sub-levels, because “Standard” can mean very different things depending on finish, glazing, and structural complexity.
| Level | Sub-level | Base UK price (£/m²) | What it means |
|---|---|---|---|
| Budget | 1 | £1,450 | Entry-level materials, local contractor, minimal spec |
| Budget | 2 | £1,650 | Slightly improved finish, still basic |
| Budget | 3 | £1,850 | Upper budget — most common “cheap quote” range |
| Budget | 4 | £2,100 | Top of budget tier |
| Standard | 1 | £2,250 | Mid-market entry, typical UK contractor |
| Standard | 2 | £2,450 | Good materials, standard glazing |
| Standard | 3 | £2,650 | Most common choice for family extensions |
| Standard | 4 | £2,850 | Upper standard, better fittings |
| Premium | 1 | £3,000 | Quality materials, experienced contractor |
| Premium | 2 | £3,250 | Full compliance, upgraded structural work |
| Premium | 3 | £3,500 | Higher-spec glazing and finishes |
| Premium | 4 | £3,750 | Top of premium tier |
| Luxury | 1 | £4,000 | Architect-led, top specification |
| Luxury | 2 | £4,300 | Full project management |
| Luxury | 3 | £4,700 | Bespoke design elements |
| Luxury | 4 | £5,200+ | High-end residential, no compromises |
Source: DEH & P Extension & Loft Conversion Price Guide, June 2026. These are UK-average base prices before regional adjustment — see zone multipliers below.
Regional Zone Multipliers
The same extension costs a different amount depending on where you live. Multiply the base price above by your zone’s multiplier:
| Zone | Multiplier | Covers |
|---|---|---|
| London Zone 1–2 | ×1.5 – 1.8 | Mayfair, Chelsea, Kensington, Westminster |
| London Zone 3–4 | ×1.3 – 1.5 | Clapham, Fulham, Hackney, Battersea |
| London Zone 5–6 | ×1.1 – 1.3 | Croydon, Barnet, Bromley, Harrow |
| South East England | ×1.0 – 1.2 | Surrey, Kent, Hertfordshire |
| Rest of England | ×0.85 – 1.0 | Midlands, North, South West |
| Scotland / Wales | ×0.80 – 0.95 | Regional adjustment applied |
Worked example: A 30m² single-storey rear extension, Budget level 3, in London Zone 3–4: £1,850/m² × ~1.4 zone multiplier ≈ £2,600/m² × 30m² = £78,000
For your exact postcode and size, use the calculator tool on this site — it applies your precise zone automatically.
What’s Included at Every Level
- Labour and materials for the structural build
- Standard compliance costs (building regulations)
- VAT (20%, included in all figures above)
- Contingency: 5% (Budget) / 10% (Standard) / 15% (Premium) / 20% (Luxury)
What’s NOT Included
- Kitchen or bathroom fit-out inside the new space (priced separately)
- Furniture, appliances, decoration
- Site-specific costs: difficult access, existing structural issues found on survey
- Architect / planning consultant fees — add +12% if you want a dedicated architect managing the project (recommended for double-storey and side-return extensions)
Planning Permission & Building Control
- Rear extension (single storey, within permitted development limits): may not need planning permission, but always needs Building Control sign-off
- Rear extension (double storey) and side return: planning permission almost always required
- Wrap-around: planning permission required — combines rear and side, exceeds most permitted development allowances
- Garage conversion: usually permitted development, but check if garage is attached and whether it affects parking requirements locally
Confirm with your local planning authority before committing — permitted development rules vary by property and by council.
Impact on Property Value
A well-executed rear extension typically adds more to property value than it costs, particularly in London zones where extra floor space is at a premium. A poorly executed one — wrong style for the street, no planning permission, corners cut on structural work — can actively reduce value at resale. See our full Property Value Impact guide for zone-by-zone figures.
Hidden Costs to Budget For
Common items that appear once work starts and aren’t in the base extension price:
- Structural steel (RSJ) if removing a load-bearing wall to open into the extension
- Drainage relocation if the extension sits over existing pipework
- Party wall agreement costs if you share a boundary wall with a neighbour
- Temporary roof/weatherproofing during build in wet months
All figures are indicative estimates for budgeting purposes only. Actual costs depend on site conditions, structural survey, planning requirements and contractor pricing. Always obtain at least three written quotes. Costs last reviewed: June 2026. Next review: September 2026.
Want your exact number? Use the free cost calculator on this site — enter your postcode and project size for a precise, zone-adjusted estimate in seconds.