How Much Does a Rear Extension Cost? [2026 Prices]
If you're thinking about extending your home, you're probably wondering: how much does a rear extension actually cost in 2026?
The short answer: £1,800–£2,800 per square metre for a typical single-storey rear extension in the UK. For a standard 20 m² extension, that means a total build cost of roughly £36,000–£56,000 — excluding professional fees, VAT, and interior finishes.
But that figure shifts dramatically depending on where you live, what materials you choose, and how complex your design is. A high-spec kitchen extension in London could top £3,500/m², while a simpler build in the North of England might come in closer to £1,600/m².
At Suddeco Homes, our AI-powered platform reads your UK address and shows you exactly what similar projects have cost nearby — based on real, approved planning applications. We then generate instant renders, architect-quality concept drawings, and priced designs. Get your free render here.
Table of Contents
- Rear Extension Cost per m² (2026)
- Cost Breakdown Table: Min / Average / Max
- Location-Specific Pricing
- What Affects the Cost of a Rear Extension?
- How to Save Money on Your Rear Extension
- Professional Fees & Hidden Costs
- Planning Permission & Building Regulations
- How Suddeco Helps You Budget Accurately
- Frequently Asked Questions
Rear Extension Cost per m² (2026)
Per-square-metre pricing is the industry standard for estimating extension costs. According to the Federation of Master Builders and Checkatrade, UK construction costs have stabilised after the post-pandemic volatility, but regional variations remain significant.
For a rear extension specifically, the 2026 cost range is:
- Standard specification: £1,800–£2,200/m²
- Mid-range specification: £2,200–£2,500/m²
- High-specification: £2,500–£2,800/m²
A kitchen extension — the most popular type of rear extension — typically sits at the higher end of that range due to plumbing, electrics, and appliance integration:
- Kitchen extension: £2,000–£3,000/m²
Quick estimate: A 4m × 5m (20 m²) rear extension at £2,200/m² = £44,000 build cost. Add 10–15% contingency and professional fees, and you're looking at approximately £50,000–£55,000 all-in.
Cost Breakdown Table: Min / Average / Max
The table below shows total project costs for common rear extension sizes. These figures include construction, VAT, professional fees, and a 10% contingency.
| Size (m²) | Description | Minimum Cost | Average Cost | Maximum Cost |
|---|---|---|---|---|
| 10 m² | Small rear extension (3m × 3.3m) | £22,000 | £27,000 | £33,000 |
| 15 m² | Medium-small extension (3m × 5m) | £32,000 | £40,000 | £48,000 |
| 20 m² | Standard extension (4m × 5m) | £41,000 | £50,000 | £61,000 |
| 25 m² | Large single-storey (5m × 5m) | £50,000 | £61,000 | £74,000 |
| 30 m² | Large rear extension (6m × 5m) | £59,000 | £72,000 | £87,000 |
| 40 m² | Very large / wrap-around element | £76,000 | £93,000 | £112,000 |
Sources: Checkatrade (2026), FMB Cost Guide, HomeOwners Alliance.
These totals include: - Construction labour and materials - VAT at 20% (where applicable) - Planning permission fees (£206 for householder applications) - Building regulations approval (£200–£1,000) - Structural engineer (£500–£2,000) - Architect fees (5–10% of build cost, or Suddeco's fixed-price design packages) - 10% contingency
Location-Specific Pricing
Where you live in the UK has one of the biggest impacts on your rear extension cost. Labour rates, material delivery, and local demand all vary significantly.
London
- Premium: +30–50% on base costs
- Typical cost: £2,500–£3,500/m²
- 20 m² total project: £55,000–£75,000
- Context: London labour rates are the highest in the UK. Parking restrictions, skip permits, and logistics add further costs. Boroughs like Kensington & Chelsea, Westminster, and Camden have additional planning constraints.
South East (Surrey, Kent, Berkshire, Hampshire, Buckinghamshire)
- Premium: +20–30% on base costs
- Typical cost: £2,200–£2,800/m²
- 20 m² total project: £48,000–£62,000
- Context: Strong demand from commuter belt homeowners. Conservation areas are common, which may increase design costs.
South West (Bristol, Devon, Cornwall, Somerset)
- Typical cost: £1,900–£2,500/m²
- 20 m² total project: £42,000–£55,000
- Context: Generally lower than London but higher than the North. Rural locations may incur travel costs for specialist trades.
Midlands (Birmingham, Nottingham, Leicester, Coventry)
- Typical cost: £1,700–£2,200/m²
- 20 m² total project: £38,000–£48,000
- Context: Competitive builder market keeps costs reasonable. Good availability of materials.
North of England (Manchester, Leeds, Newcastle, Liverpool, Sheffield)
- Discount: -10–15% on base costs
- Typical cost: £1,600–£2,100/m²
- 20 m² total project: £35,000–£46,000
- Context: Lower labour costs and strong local builder networks. Some urban areas have higher costs due to narrow access.
Scotland (Edinburgh, Glasgow, Aberdeen, Dundee)
- Discount: -10–20% on base costs
- Typical cost: £1,600–£2,000/m²
- 20 m² total project: £35,000–£44,000
- Context: Edinburgh costs approach South East levels due to demand and conservation pressures. Glasgow and other cities are more affordable.
Suddeco tip: Enter your address on our platform and we'll show you what neighbours paid for similar extensions — no guesswork, no averages that don't apply to you. Try it free.
What Affects the Cost of a Rear Extension?
Several factors push your project up or down the cost spectrum. Understanding these helps you make informed trade-offs.
1. Size
Larger extensions cost more in total but often less per square metre due to economies of scale. A 30 m² extension might cost £2,000/m², while a 10 m² extension could cost £2,400/m² because fixed costs (foundations, connecting to existing structure, setting up the site) are spread over fewer square metres.
2. Specification & Materials
- Standard: Brick/block walls, concrete floor, flat roof with EPDM, basic uPVC windows, standard kitchen — £1,800–£2,200/m²
- Mid-range: Rendered block, engineered timber floor, pitched roof with tiles, aluminium bi-fold doors, mid-range kitchen — £2,200–£2,500/m²
- High-spec: Full glazing, underfloor heating, smart home integration, bespoke kitchen, architectural details — £2,500–£2,800/m²+
3. Foundation Type
- Standard strip foundations: Included in base cost
- Reinforced foundations (poor soil, trees nearby): +£2,000–£5,000
- Piled foundations: +£5,000–£10,000
- Basement under extension: +£15,000–£30,000
4. Roof Type
- Flat roof (EPDM or GRP): Standard, included in base cost
- Pitched roof (tiles/slates): +£1,500–£3,000
- Roof lantern / skylights: +£500–£2,000 each
5. Doors & Windows
- Standard French doors: Included in base cost
- Aluminium bi-fold doors (3-panel): +£2,000–£4,000
- Crittall-style steel doors: +£3,000–£6,000
- Large glazed gable: +£3,000–£8,000
6. Kitchen & Utilities
If you're adding a kitchen, budget for: - Kitchen units & worktops: £5,000–£20,000+ - Appliances: £2,000–£8,000 - Plumbing & electrics: £2,000–£5,000 - Underfloor heating: £1,500–£3,000
7. Access & Site Constraints
- Narrow side access: May require manual material handling, adding labour costs
- No rear access (terrace house): Materials must come through the house, adding time and protection costs
- Party wall agreement required: £700–£2,000
- Tree Preservation Orders (TPOs): May require specialist foundation design
- Parking suspension / skip permits: £100–£500 depending on location
8. Complexity of Design
- Simple rectangular box: Most cost-effective
- L-shaped or irregular footprint: More complex structure, higher cost
- Single storey: £1,800–£2,800/m²
- Double-storey rear extension: £1,800–£2,500/m² (but more total m², so higher overall cost)
- Wrap-around (rear + side return): £2,000–£3,000/m² — see our side return extension cost guide
How to Save Money on Your Rear Extension
You don't need to compromise on quality to control costs. Here are proven strategies:
1. Get Your Design Right First Time
Revisions during construction are expensive. A well-thought-out design prevents costly changes. Our Concept Package delivers 3 renders, full plans, and one revision in 48 hours — so you know exactly what you're building before anyone lifts a trowel.
2. Use Our AI to See What Neighbours Paid
Suddeco analyses approved planning applications near your address to show you real cost benchmarks for your specific street. No more relying on national averages that don't fit your situation. Get your free render.
3. Choose a Fixed-Price Design Package
Traditional architects charge 5–10% of build cost, which can be £3,750–£7,500 for a typical £75k extension. Our Design+Planning package is a fixed £2,495 — including planning application, building regulations, structural engineer, and unlimited revisions.
4. Time Your Build Wisely
- Avoid peak season: Builders are busiest March–September. Starting in October–February can secure better rates.
- Book early: Good builders are booked 3–6 months ahead. Last-minute bookings often cost more.
5. Consider Material Choices
- uPVC windows vs. aluminium: Save £1,000–£2,000
- Standard kitchen vs. bespoke: Save £5,000–£10,000
- Flat roof vs. pitched roof: Save £1,500–£3,000
- Standard patio doors vs. bi-folds: Save £1,500–£3,000
6. Keep the Shape Simple
A rectangular box is the most cost-effective shape. Every corner, jog, and level change adds complexity and cost.
7. Do Some Work Yourself (if qualified)
- Painting & decorating: Save £2,000–£4,000
- Tiling: Save £1,000–£2,000
- Landscaping: Save £1,000–£3,000
- Caution: Never DIY structural, electrical, or gas work. These must be certified.
8. Get Multiple Builder Quotes
We recommend 3–4 detailed quotes. Our Design-to-Build service connects you with vetted builders who have been assessed for quality, reliability, and fair pricing — plus we provide milestone payment protection and a 12-month warranty.
Professional Fees & Hidden Costs
Beyond construction, budget for these essentials:
| Item | Cost | Notes |
|---|---|---|
| Planning permission (householder) | £206 | Required if not permitted development |
| Planning permission (full) | £462 | For listed buildings or complex sites |
| Building regulations | £200–£1,000 | Mandatory for all structural work |
| Structural engineer | £500–£2,000 | For calculations and beam design |
| Party wall surveyor | £700–£2,000 | If adjoining properties are affected |
| Architect (traditional) | 5–10% of build cost | £3,750–£7,500 for typical £75k extension |
| Building surveyor | £500–£1,500 | Optional but recommended for older properties |
| Contingency | 10–15% of build cost | Essential for unforeseen issues |
| VAT | 20% | On labour and materials (some builders offer VAT-inclusive pricing) |
Planning Permission & Building Regulations
Permitted Development
Many rear extensions fall under permitted development rights, meaning you don't need full planning permission if you meet these criteria: - Single storey - Maximum depth: 4m (detached) or 3m (other houses) from original rear wall - Maximum height: 4m - Materials similar to existing house - Not on designated land (national parks, AONBs, conservation areas — where rules are stricter)
Important: Permitted development still requires a Lawful Development Certificate (£103) to prove compliance — essential when selling your home.
Full Planning Permission
If your extension exceeds permitted development limits, or you're in a conservation area, you'll need householder planning permission (£206). The process typically takes 8–12 weeks.
Building Regulations
All extensions must comply with Building Regulations, covering: - Structural integrity - Thermal insulation (U-values) - Fire safety - Ventilation - Drainage
You'll need either a Building Notice (simpler, less detail) or Full Plans Approval (recommended for extensions). Cost: £200–£1,000 depending on your local authority.
How Suddeco Helps You Budget Accurately
Most homeowners start with a vague idea of cost and end up with nasty surprises. Suddeco changes that:
- Enter your address — our AI analyses nearby approved planning applications to show what similar projects actually cost in your area.
- Get a free instant render — see your extension visualised on your actual home, with plans and a cost estimate. Start here.
- Choose your design package — our Concept Package (£495 or £995 depending on complexity) delivers 3 renders, full plans, and a revision in 48 hours. Our Design+Planning package (£2,495) includes everything for your planning application.
- Connect with vetted builders — our Design-to-Build service matches you with trusted builders, with milestone payment protection and a 12-month warranty.
No more guesswork. No more "how much will this actually cost?" anxiety. Just clear, data-driven pricing based on real projects near you.
Frequently Asked Questions
How much does a 20 m² rear extension cost in 2026?
A 20 m² rear extension costs approximately £41,000–£61,000 all-in, including construction, VAT, professional fees, and a 10% contingency. In London, expect £55,000–£75,000. In the North of England or Scotland, £35,000–£48,000 is typical.
Is a rear extension worth the money?
Yes — a well-designed rear extension typically adds 15–20% to your home's value, according to the HomeOwners Alliance. For a £400,000 property, a £50,000 extension could add £60,000–£80,000 in value, plus you gain living space without moving.
How long does a rear extension take to build?
A typical single-storey rear extension takes 10–14 weeks from breaking ground to completion. Planning permission (if required) adds 8–12 weeks beforehand. Design and preparation add another 4–8 weeks. Total timeline: 5–8 months from initial design to moving in.
Do I need planning permission for a rear extension?
Not always. Many rear extensions fall under permitted development if they're single-storey, no more than 4m deep (detached) or 3m deep (other houses), and under 4m high. However, you still need Building Regulations approval, and a Lawful Development Certificate is recommended for future resale.
What's the cheapest way to build a rear extension?
The most cost-effective approach is: (1) keep the design simple (rectangular, single storey), (2) use standard materials, (3) avoid complex foundations, (4) get a fixed-price design package, and (5) book your builder outside peak season. Our free render shows you exactly what neighbours built and what they paid, so you can make informed choices.
Can I build a rear extension myself?
You can act as the project manager and do some finishing work (painting, decorating, tiling) yourself, but structural work, electrics, and gas must be done by qualified professionals and certified. Most lenders and buyers will want to see Building Regulations completion certificates and warranties.
Does a rear extension add value to my house?
Yes. A rear extension typically adds 15–20% to property value, with kitchen extensions at the higher end. The key is matching the quality and style to your home and the local market. A £50,000 extension on a £400,000 house could add £60,000–£80,000 in value.
How much does a kitchen extension cost compared to a standard rear extension?
Kitchen extensions cost £2,000–£3,000/m² compared to £1,800–£2,800/m² for a standard rear extension. The premium comes from plumbing, electrics, appliance integration, and typically higher-spec finishes. A 20 m² kitchen extension typically costs £45,000–£65,000 all-in.
What are the hidden costs of a rear extension?
Common hidden costs include: party wall agreements (£700–£2,000), tree surveys (if TPOs apply), parking suspensions, skip permits, connecting to existing utilities, upgrading the boiler, and unforeseen structural issues (hence the 10–15% contingency). Our Design+Planning package includes structural engineer and planning fees, so fewer surprises.
How much does a rear extension cost in London vs. the North?
London rear extensions cost £2,500–£3,500/m² (30–50% premium), while the North of England averages £1,600–£2,100/m² (10–15% discount). For a 20 m² extension, that's roughly £55,000–£75,000 in London vs. £35,000–£46,000 in the North — a £20,000+ difference.
Can I get a fixed-price quote for my rear extension?
Some builders offer fixed-price contracts, but these are often based on detailed plans. We recommend getting our Concept Package first to lock down your design, then requesting fixed-price builder quotes. Our Design-to-Build service includes vetted builders with clear pricing and milestone payment protection.
What's the difference between a rear extension and a wrap-around extension?
A rear extension extends straight back from the rear wall. A wrap-around combines a rear extension with a side return extension, creating an L-shaped addition. Wrap-arounds cost £2,000–£3,000/m² but transform terraced houses by bringing light into the centre of the home. See our side return extension cost guide for more details.
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