Extension Costs UK 2026: Complete Price Guide
Every Extension Type Priced, from Single-Storey Rear to Double-Storey Wraparound
Quick Answer
A single-storey rear extension in the UK costs £25,000 to £50,000 on average. Two-storey extensions cost £40,000 to £90,000. The biggest cost factors are size (£1,500 to £2,500 per m2), your region (London adds 25-35%), and the spec level you choose.
House extensions are one of the most popular home improvement projects in the UK, and for good reason. Adding space to your home is often more cost-effective than moving, especially once you factor in stamp duty, estate agent fees, and the upheaval of relocation.
The challenge is that extension costs vary enormously. A straightforward single-storey rear extension might cost £25,000 in the North of England or £55,000 in London for essentially the same specification. Understanding what drives these differences helps you plan a realistic budget and have better conversations with your builder.
This guide breaks down real 2026 UK extension prices by type, region, and spec level, so you know what to expect before getting quotes.
In This Guide
- Extension costs by type: rear, side return, wraparound, and two-storey
- Regional price differences across the UK
- Detailed cost breakdown by construction stage
- Planning permission and building regulations guidance
- How to budget effectively and avoid common surprises
- Whether an extension adds value to your property
Extension Costs by Type
The type and size of extension you build is the single biggest factor in total cost. A small rear extension adding a kitchen-diner is a very different project from a double-storey wraparound. Here are 2026 prices across three spec levels.
| Extension Type | Budget | Mid Range | Premium |
|---|---|---|---|
| Small Rear (3-4m) | £20,000 to £30,000 | £30,000 to £45,000 | £45,000 to £65,000 |
| Medium Rear (4-6m) | £30,000 to £45,000 | £45,000 to £65,000 | £65,000 to £90,000 |
| Large Rear (6-8m) | £45,000 to £60,000 | £60,000 to £85,000 | £85,000 to £120,000+ |
| Side Return | £25,000 to £35,000 | £35,000 to £50,000 | £50,000 to £70,000 |
| Wraparound (rear + side) | £50,000 to £70,000 | £70,000 to £100,000 | £100,000 to £150,000+ |
| Two-Storey Rear | £40,000 to £60,000 | £60,000 to £90,000 | £90,000 to £130,000+ |
Prices include build costs, professional fees, and VAT. London and South East prices are typically 25% to 35% higher than the figures shown.
Regional Price Differences
Location has a significant impact on extension costs. Labour rates vary by up to 40% across the UK, and London commands the highest prices. Material costs are more consistent nationally, but labour is the dominant factor.
| Region | Cost per m2 | Small Rear Avg | Two-Storey Avg |
|---|---|---|---|
| London | £2,200 to £3,000 | £40,000 to £55,000 | £65,000 to £100,000 |
| South East | £1,800 to £2,500 | £35,000 to £48,000 | £55,000 to £85,000 |
| South West | £1,600 to £2,200 | £30,000 to £42,000 | £50,000 to £75,000 |
| Midlands | £1,500 to £2,000 | £28,000 to £38,000 | £45,000 to £70,000 |
| North England | £1,400 to £1,900 | £25,000 to £35,000 | £40,000 to £65,000 |
| Scotland | £1,500 to £2,100 | £28,000 to £40,000 | £45,000 to £72,000 |
| Wales | £1,400 to £1,900 | £25,000 to £36,000 | £42,000 to £65,000 |
Why Such Variation?
- Labour rates: London builders charge 30% to 40% more than those in the North due to higher living and business costs
- Land values: In higher-value areas, homeowners invest in better specifications, which pushes average prices up
- Demand: Areas with high renovation demand (London, South East) have less builder availability, increasing prices
What Affects the Price? Full Cost Breakdown
Understanding where your money goes helps you make informed decisions about where to invest and where to save. Here is a breakdown by construction stage for a typical single-storey rear extension.
Planning Permission & Building Regulations
Know Before You Start
Permitted Development: Most single-storey rear extensions up to 4m (or 6m with prior notification for detached houses) fall under Permitted Development and do not need planning permission. Two-storey extensions, side extensions closer than 2m to a boundary, and anything in conservation areas typically do need planning.
Building Regulations: Building regulations approval is required for ALL extensions regardless of planning permission status. Budget £500 to £1,000 for building control fees.
Party Wall: If your extension is near a neighbour's property, you may also need a Party Wall Agreement. This costs £800 to £2,000 per neighbour for the surveyor.
Usually Permitted Development
- Single-storey rear up to 4m (attached house)
- Single-storey rear up to 6m (detached, with prior notification)
- Max height 4m for single-storey
- Not forward of the principal elevation
Usually Needs Planning
- Two-storey extensions
- Side extensions within 2m of boundary
- Properties in conservation areas
- Listed buildings (also needs listed building consent)
- Extensions covering more than 50% of garden
How to Budget for Your Extension
Extensions are significant investments. These practical tips will help you budget effectively and avoid the most common financial surprises.
Get 3 Quotes Minimum
Provide each builder with the same specification so quotes are comparable. A detailed spec avoids misunderstandings later.
Add 10% to 15% Contingency
Unexpected costs are almost guaranteed. Ground conditions, structural issues discovered during work, and material price changes are the most common surprises.
Budget Professional Fees Separately
Architect, structural engineer, and building control add 8% to 12% to the build cost. These are not included in most builder quotes.
Plan for Hidden Costs
Skip hire (£250 to £400), temporary kitchen if extending kitchen (£50/week), landscaping restoration (£1,000 to £3,000), and utility reconnections.
Staged Payments Are Normal
Typical schedule: 10% at start, then staged payments at foundations, first floor, roof-on, first fix, and completion. Never pay more than the value of work completed.
Hidden Costs to Remember
Does an Extension Add Value?
Return on Investment
A well-designed extension typically adds 5% to 15% to your property's value, though this depends on your area, the quality of the build, and whether you have maximised the planning potential.
A single-storey rear extension adding a kitchen-diner is one of the best ROI projects. It creates the open-plan living space that most buyers now expect, and the cost is often recouped in full when you sell.
However, over-extending (using most of your garden) can actually reduce value. Buyers value outdoor space, so leaving a usable garden is important. Similarly, exceeding the ceiling price for your street means you may not recoup the full investment.
Best ROI
Kitchen-diner rear extension
+8% to 15%Good ROI
Extra bedroom (two-storey)
+5% to 12%Variable ROI
Large wraparound extension
+3% to 10%Key Takeaways
Calculate Your Extension Budget
Use our free renovation calculator to get a personalised estimate based on your location, extension type, and specification.
Try the CalculatorRelated Guides
Kitchen Renovation Costs UK
Detailed pricing guide for kitchen renovations by size and quality.
Building Regulations Explained
Everything you need to know about building regs for your project.
Do I Need Planning Permission?
Find out if your project needs planning permission or falls under PD.
How to Budget for Your Renovation
Practical budgeting framework for any home improvement project.
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