London Extension Costs 2026: The Complete Price Guide
Real extension prices for 2026 based on current builder quotes and completed projects. From single-storey rears to basement conversions, here is what you will actually pay in London.
Quick Answer
In 2026, London extensions cost £3,200-£4,600 per m². Single-storey rear: £60k-135k, loft conversion: £52k-100k, two-storey: £110k-290k. Prices are up 3-4% from 2025 due to labour cost inflation.
£3,200-£4,600
Per m² Cost
£60k-£135k
Single Storey
£110k-£290k
Two Storey
Check your specific property constraints
Free Property Check2026 Construction Market Overview
Construction costs in London have risen approximately 3-4% from 2025 to 2026. This follows the pattern of steady increases since 2022, driven primarily by labour costs rather than materials.
Key 2026 trend: Labour costs are up 7% year-on-year, with skilled tradespeople in high demand. Material costs have stabilised but remain elevated. Builder capacity is still constrained, meaning lead times of 3-6 months are common for reputable contractors.
What is Driving 2026 Prices?
- Labour inflation: Skilled tradespeople wages continue rising above general inflation
- Building Regs 2025: Updated Part L insulation requirements add 2-3% to build costs
- Capacity constraints: Good builders are booked 3-6 months ahead
- Materials stable: Most materials flat, but metals 6-10% above 2024 lows
Check if you need planning permission
Free instant estimate based on your property, location, and project size. Updated with 2026 pricing.
Cost Per Square Metre in 2026
London extension costs in 2026 range from £3,200 to £4,600 per m² depending on specification and complexity.
| Specification Level | Cost/m² (2026) | What is Included |
|---|---|---|
| Budget | £3,200 - £3,600 | Standard materials, basic finishes, painted walls |
| Mid-Range | £3,600 - £4,200 | Quality finishes, engineered flooring, good lighting |
| High-End | £4,200 - £4,600 | Premium materials, underfloor heating, smart home features |
| Premium | £4,600+ | Architect-designed, bespoke joinery, high-spec glazing |
Important: These m² rates cover construction only. Add 10-15% for professional fees (architect, structural engineer), plus your kitchen/bathroom fit-out, plus 10% contingency. See our guide to hidden costs of London extensions for a full breakdown.
Extension Costs by Type (2026)
Single-Storey Rear Extension
The most popular extension type in London. A rear extension creates open-plan kitchen-diners or larger living spaces.
Two-Storey Rear Extension
A two-storey extension adds both ground floor space and an extra bedroom or bathroom above. Best value per m² but requires planning permission.
Loft Conversion
No foundation costs make a loft conversion excellent value. Converts unused roof space into bedroom(s) with en-suite.
Side Return Extension
A side return extension fills the narrow alley beside terraced houses. Widens the kitchen significantly for a modern open-plan layout.
Wrap-Around (Side + Rear)
A wrap-around extension combines side return with rear extension for maximum ground floor space. Popular with Victorian terraces.
Basement Extension
A basement extension is the most expensive per m² but creates significant space without reducing garden. Complex engineering required.
Not sure if you need planning permission? Our AI can check your property in 2 minutes.
Check now — it's freeWhat is Included (and What is Not)
Typically Included
- Foundations and groundworks
- Walls, roof, and structure
- Windows and external doors
- First-fix electrics and plumbing
- Plastering and decoration
- Basic floor finish
Usually Extra
- Kitchen units and appliances
- Architect fees (8-12%)
- Structural engineer (£1.5k-3k)
- Party wall agreements (£1k-3k)
- Planning fees (£258-500)
- Landscaping and paving
Costs by London Area (2026)
Extension costs vary by area due to local builder rates, access constraints, and parking zone requirements:
| Area | Cost Variation | Notes |
|---|---|---|
| Prime Central | +15-25% | Kensington, Chelsea, Westminster - premium builder rates |
| Inner London | +5-15% | Islington, Hackney, Camden - access challenges, parking |
| South London | Baseline | Lewisham, Greenwich, Southwark - average costs |
| Outer London | -5-10% | Bromley, Croydon, Barnet - better access, lower rates |
| Conservation Areas | +5-10% | Higher design standards, matching materials required |
Free AI Assistant
Ask anything about your extension
How to Budget Your Extension
The Real Total Cost Formula
Here is how to calculate a realistic budget for your 2026 London extension:
Example: 25m² Single-Storey Extension (2026)
Frequently Asked Questions
How much does a house extension cost in London in 2026?
In 2026, London house extensions typically cost £3,200-£4,600 per m². A single-storey rear extension costs £60,000-£135,000, a loft conversion £52,000-£100,000, and a two-storey extension £110,000-£290,000. Prices increased approximately 3-4% from 2025 due to labour cost inflation.
What is the cost per square metre for an extension in London 2026?
London extension costs per m² in 2026 range from £3,200 for basic single-storey builds to £4,600+ for high-specification finishes. Two-storey extensions cost £3,400-£4,200/m² due to additional structural requirements.
How much has construction cost increased in London for 2026?
Construction costs in London have risen approximately 3-4% from 2025 to 2026. This is primarily driven by labour cost inflation (up 7% year-on-year) and capacity constraints in the construction sector.
What is the cheapest type of extension in London?
The most cost-effective extension per m² is a single-storey rear extension at £3,200-£3,800/m². However, for total project cost, a small side return (8-12m²) or a loft conversion can offer better value for the space gained.
Should I get multiple quotes for my London extension?
Yes, always get 3-4 quotes from reputable builders. In London's 2026 market, quotes can vary by 20-30% for the same project. Compare like-for-like specifications and check what is included.
Summary: 2026 Extension Costs
London extension costs in 2026 have increased 3-4% from 2025, driven primarily by labour cost inflation. For a typical mid-range project, budget:
- Single-storey rear: £95,000-£130,000 all-in
- Loft conversion: £65,000-£95,000 all-in
- Two-storey: £165,000-£250,000 all-in
Start with accurate pricing before commissioning designs. Use our free cost calculator to get a personalised estimate based on your property type, location, and project requirements.
Ready to start?
Get your extension estimate in 2 minutes
Find out exactly how much your London extension will cost. Our AI assistant provides instant, personalised quotes based on current market rates.
Or email hello@mayfairstudio.co.uk · 07405 920944