How Much Does a Single-Storey Extension Cost? [2026 UK Prices]
A single-storey extension is one of the most popular ways to add space and value to a UK home. Whether you're dreaming of a spacious kitchen-diner, a bright home office, or an extra living room, understanding the true cost before you start is essential.
According to Checkatrade and the Federation of Master Builders (FMB), the average construction cost for a single-storey extension in the UK in 2026 ranges from £1,800 to £2,800 per square metre. That means a typical 20 m² extension costs between £36,000 and £56,000 to build, with total project costs typically reaching £45,000 to £65,000 once you factor in VAT, planning fees, building regulations, and professional services.
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Table of Contents
- What is a Single-Storey Extension?
- Single-Storey Extension Cost Breakdown (2026)
- Cost by Location: London, South East, North & Scotland
- What Affects the Cost of a Single-Storey Extension?
- Additional Costs to Budget For
- How to Save Money on Your Single-Storey Extension
- Why Choose Suddeco for Your Extension?
- Frequently Asked Questions
What is a Single-Storey Extension?
A single-storey extension extends your home outward at ground level. Common configurations include:
- Rear extension: Built at the back of the house, often opening into the garden
- Side return extension: Filling in the alleyway at the side of a terraced or semi-detached house
- Wrap-around extension: Combining rear and side return for maximum space
- Front extension: Less common but useful for porches or enlarged entrances
Single-storey extensions are generally more affordable than double-storey options and often fall within permitted development rights, meaning you may not need full planning permission.
Related reading: How much does a double-storey extension cost?
Single-Storey Extension Cost Breakdown (2026)
The table below shows construction costs only. Total project costs including VAT, fees, and finishes are typically 25–35% higher.
| Size | Dimensions | Area (m²) | Low (£/m²) | Average (£/m²) | High (£/m²) | Build Cost (Low) | Build Cost (High) | Total Project Cost* |
|---|---|---|---|---|---|---|---|---|
| Small | 3 m × 4 m | 12 | £1,800 | £2,200 | £2,800 | £21,600 | £33,600 | £28,000–£42,000 |
| Medium | 4 m × 5 m | 20 | £1,800 | £2,200 | £2,800 | £36,000 | £56,000 | £45,000–£65,000 |
| Large | 5 m × 6 m | 30 | £1,800 | £2,200 | £2,800 | £54,000 | £84,000 | £65,000–£95,000 |
| Extra Large | 6 m × 8 m | 48 | £1,800 | £2,200 | £2,800 | £86,400 | £134,400 | £100,000–£150,000 |
*Total project cost includes construction, VAT (20%), planning fees, building regulations, professional fees, and standard finishes.
According to the HomeOwners Alliance, a typical 20 m² single-storey extension in the UK in 2026 will cost between £45,000 and £65,000 all-in, making it one of the most cost-effective ways to add significant living space.
Cost Per Square Metre Explained
The £1,800–£2,800/m² range reflects the difference between a basic finish and a high-specification build. At the lower end, you can expect standard brickwork, basic windows, and simple flooring. At the higher end, you'll get bi-fold doors, premium glazing, underfloor heating, and bespoke finishes.
Cost by Location: London, South East, North & Scotland
Construction costs vary significantly across the UK. Labour rates, material costs, and demand all play a role.
| Region | Premium / Discount | Cost per m² (2026) | Total Cost (20 m²) |
|---|---|---|---|
| London | +30–50% | £2,340–£4,200 | £50,000–£80,000 |
| South East | +20–30% | £2,160–£3,640 | £48,000–£72,000 |
| Midlands | –10–20% | £1,440–£2,520 | £38,000–£55,000 |
| North England | –10–20% | £1,440–£2,520 | £38,000–£55,000 |
| Scotland | –10–20% | £1,440–£2,520 | £38,000–£55,000 |
London commands the highest premiums due to labour shortages, access constraints, and higher material costs. If you're building in Kensington, Chelsea, or Westminster, expect to pay at the top end. For more affordable options, the Midlands and North offer excellent value, with quality builders available at lower rates.
What Affects the Cost of a Single-Storey Extension?
Several factors influence where your project falls within the £1,800–£2,800/m² range:
1. Size and Footprint
Larger extensions benefit from economies of scale, but the cost per square metre remains relatively consistent. The fixed costs (foundations, roofing, and services) are spread over a larger area.
2. Materials and Finishes
- Standard specification: White uPVC windows, laminate flooring, basic kitchen units → lower end of range
- High specification: Aluminium bi-fold doors, engineered wood flooring, bespoke kitchen → upper end
3. Location
As shown above, London and the South East are significantly more expensive than the North and Midlands.
4. Complexity and Access
Difficult access, restricted working space, or complex groundwork (e.g., sloping sites, poor soil) can push costs up by 10–20%.
5. Glazing and Doors
Bi-fold or sliding doors cost £1,500–£4,000 per linear metre installed. A 4-metre opening could add £6,000–£16,000 to your budget.
6. Roofing Type
- Flat roof with EPDM membrane: £80–£120/m²
- Pitched roof with tiles: £120–£180/m²
- Roof lantern: £1,000–£3,000 each
7. Kitchen or Bathroom Integration
Adding a kitchen (£5,000–£25,000) or bathroom (£3,000–£10,000) significantly increases costs.
8. Ground Conditions
Poor soil, high water tables, or nearby trees may require deeper foundations or piling, adding £2,000–£10,000.
Additional Costs to Budget For
Beyond the build cost, budget for these essential extras:
| Item | Cost (2026) |
|---|---|
| Planning permission (householder) | £206 |
| Planning permission (full application) | £462 |
| Building regulations approval | £200–£1,000 |
| Party wall agreement | £700–£2,000 |
| Structural engineer | £500–£2,000 |
| Architect (5–10% of build cost) | £3,750–£7,500 (typical £75k extension) |
| VAT (20% on labour and materials) | 20% of build cost |
| Contingency | 10–15% of total budget |
The HomeOwners Alliance recommends setting aside at least 10–15% as a contingency for unexpected issues.
How to Save Money on Your Single-Storey Extension
1. Start with a Free Render
Our platform generates an instant render and cost estimate from your address. Knowing what's possible — and what neighbours have approved — helps you avoid expensive redesigns later.
2. Keep the Design Simple
Rectangular shapes are cheaper than complex L-shapes or angled designs. Avoid unnecessary structural steel where possible.
3. Choose Standard Materials
Bespoke finishes look beautiful but add thousands. Standard kitchens, off-the-shelf windows, and laminate flooring can cut costs by 20–30%.
4. Plan for Off-Peak Seasons
Builders are often quieter in January and February. Booking during these months can secure better rates.
5. Use Our Design-to-Build Service
Suddeco's vetted builder network means competitive quotes, milestone payment protection, and a 12-month warranty. No middlemen, no hidden fees.
Get your free render and see what's possible →
Related reading: How much does a kitchen extension cost? | How much does a garage conversion cost?
Why Choose Suddeco for Your Extension?
Traditional routes involve weeks of architect consultations, multiple site visits, and uncertain costs. Suddeco changes this:
- Free render: Enter your address, see an instant visual of what's possible
- Concept Package (£495–£995): 3 renders, full plans, one revision, delivered in 48 hours
- Design+Planning (£2,495): Full planning application, building regulations, structural engineer, unlimited revisions
- Design-to-Build: Fee plus percentage of build cost — vetted builders, project management, milestone payment protection, 12-month warranty
Our platform reads thousands of nearby planning applications to show you what actually gets approved. No guesswork. No waiting.
Frequently Asked Questions
What is the average cost per m² for a single-storey extension in 2026?
The average cost is £2,200 per square metre, with a typical range of £1,800–£2,800/m² depending on specification and location. According to Checkatrade and FMB data, this represents a 3–5% increase on 2025 prices due to inflation and labour shortages.
How much does a 20 m² single-storey extension cost in total?
A 20 m² extension costs approximately £36,000–£56,000 to build, with total project costs of £45,000–£65,000 including VAT, fees, and finishes.
Do I need planning permission for a single-storey extension?
Often, no. Many single-storey extensions fall within permitted development rights (PDR), provided they meet certain limits: - Maximum height: 4 metres - Maximum depth: 3 metres (semi-detached) or 4 metres (detached) - Must not cover more than 50% of the garden - Must not extend beyond the rear wall by more than 3 metres (semi) or 4 metres (detached)
If your property is in a conservation area, national park, or Area of Outstanding Natural Beauty, full planning permission may be required.
How long does it take to build a single-storey extension?
Typically 8–14 weeks for construction, plus 6–12 weeks for planning and design. A simple rear extension under permitted development can start sooner. Complex projects with bespoke features may take 16–20 weeks.
Can I build a single-storey extension without hiring an architect?
Technically yes, but it's not recommended. An architect ensures the design maximises space, meets regulations, and adds value. Suddeco's concept packages start at £495 — far less than traditional architects — and include full plans and renders.
What's the difference between a single-storey and double-storey extension cost?
A double-storey extension costs roughly £1,800–£2,500/m² — slightly less per square metre than single-storey because the foundation and roof costs are shared across two floors. However, the total cost is higher because you're building twice the floor area.
Does a single-storey extension add value to my home?
Yes. According to the HomeOwners Alliance, a well-designed single-storey extension can add 10–20% to your property's value. A kitchen-diner extension often delivers the highest return.
Can I get finance or a mortgage for a single-storey extension?
Yes. Options include: - Further advance from your existing mortgage lender - Remortgaging to release equity - Home improvement loan or personal loan - Design-to-Build finance through select partners
What is permitted development for single-storey extensions?
Permitted development allows certain extensions without a full planning application. Key limits for single-storey rear extensions: - Detached houses: max 4 m depth, 4 m height - Semi-detached / terraced: max 3 m depth, 4 m height - Must not exceed 50% of total curtilage
Always check with your local planning authority before starting.
How do I get an accurate quote for my single-storey extension?
Start with Suddeco's free render. Our platform analyses your address, nearby approved applications, and local costs to generate an accurate estimate in minutes. For a fixed quote, our Design-to-Build service provides competitive bids from vetted builders.
Are there hidden costs in single-storey extensions?
Common "hidden" costs include: - Tree protection orders requiring specialist foundations - Drainage diversion - Asbestos removal in older properties - Party wall agreements - Building control inspections - Connection fees for utilities
Our £2,495 Design+Planning package includes structural engineer reports and building regulations, so you know exactly what you're paying for.
Can I live in my house during a single-storey extension build?
Yes, in most cases. Single-storey rear extensions typically don't require you to move out. However, dust, noise, and limited kitchen access can be disruptive. Many homeowners plan a holiday during the most intensive phase.
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