Rear Extension Cost per m²: The Complete 2026 UK Guide
If you are pricing a rear extension in 2026, the cost per square metre is the number that matters most. It is the benchmark every builder quotes against, the figure architects use for initial estimates, and the metric that determines whether your budget will stretch to the space you need — or leave you short.
In 2026, a single-storey rear extension in the UK costs between £1,800 and £2,800 per square metre for a standard-quality build. That figure includes construction labour, materials, and VAT at 20%. It does not include kitchen units, professional fees, or contingency.
For a true all-in cost — adding fees, finishes, and a sensible buffer — budget £2,500–£3,500 per m².
This guide breaks down exactly what drives that per-m² price, how it varies by location and specification, and how to calculate an accurate total for your specific project. All figures are consistent with 2026 industry data from Checkatrade, the Federation of Master Builders, and the HomeOwners Alliance.
Table of Contents
- What Is the Average Rear Extension Cost per m² in 2026?
- Cost per m² by Finish Level
- Cost per m² by Extension Size
- Cost per m² by Location
- Cost per m² by Extension Type
- What Is Included in the per m² Price?
- What Is NOT Included in the per m² Price?
- How to Calculate Your Total Rear Extension Cost
- How to Reduce Your Cost per m²
- Planning Permission & Building Regulations
- FAQs
What Is the Average Rear Extension Cost per m² in 2026?
The table below shows the cost per m² for rear extensions across the UK in 2026, broken down by the three most common price bands. All construction figures include VAT at 20%.
| Price Band | Cost per m² (inc. VAT) | Typical Specification |
|---|---|---|
| Budget | £1,600–£2,000 | Standard materials, minimal glazing, simple flat roof, basic windows and doors, no structural complexity |
| Mid-range | £2,000–£2,500 | Quality materials, some glazing (bi-folds or roof lantern), pitched or flat roof, good insulation |
| Premium | £2,500–£2,800+ | High-end materials, extensive glazing, complex roof, underfloor heating, architectural details |
National average (2026): £2,200 per m² (inc. VAT)
These are construction-only costs. For every £1,000 you spend on construction, you should budget an additional £300–£500 for professional fees, contingency, and any fit-out upgrades beyond the standard specification. This means a true all-in cost per m² of roughly £2,500–£3,500 for a mid-range project.
Quick Reference: Total Project Cost by Size
| Size (m²) | Budget (All-In) | Mid-Range (All-In) | Premium (All-In) |
|---|---|---|---|
| 10 m² | £22,000–£28,000 | £27,000–£33,000 | £33,000–£40,000 |
| 15 m² | £32,000–£40,000 | £40,000–£48,000 | £48,000–£58,000 |
| 20 m² | £41,000–£50,000 | £50,000–£61,000 | £61,000–£74,000 |
| 25 m² | £50,000–£61,000 | £61,000–£75,000 | £75,000–£91,000 |
| 30 m² | £59,000–£72,000 | £72,000–£88,000 | £88,000–£107,000 |
All-in totals include construction, VAT at 20%, professional fees, and a 10% contingency.
Cost per m² by Finish Level
The level of finish you choose has the single biggest impact on the cost per m² after location. Below is a detailed breakdown of what each level includes.
Budget Finish (£1,600–£2,000/m²)
- Walls: Cavity walls with insulation, brick or rendered block facing
- Windows: White uPVC double glazing
- Doors: Standard French doors or basic patio doors
- Roof: Flat roof with EPDM rubber membrane, or standard pitched roof with concrete tiles
- Flooring: Concrete slab with screed, or suspended timber floor
- Electrics: First and second fix, standard sockets and LED downlights
- Plumbing: Basic radiator extension from existing boiler
- Decoration: White emulsion walls and ceilings, standard woodwork finish
- Suitable for: Rental properties, tight budgets, or extensions used as utility space, playrooms, or basic home offices.
Mid-Range Finish (£2,000–£2,500/m²)
- Walls: Cavity walls with enhanced insulation, brick or rendered finish matching existing house
- Windows: Aluminium or timber-effect uPVC
- Doors: Aluminium bi-fold or sliding doors (2.5–4 m width)
- Roof: Pitched roof with slate or clay tiles, or flat roof with single-ply membrane and one roof lantern
- Flooring: Concrete slab with insulation and screed, ready for final flooring
- Electrics: Enhanced electrics, additional sockets, under-cabinet lighting circuit
- Plumbing: Extended heating system, possible underfloor heating zone
- Decoration: Plaster finish, ready for homeowner decoration or included white emulsion
- Suitable for: Most family homes. This is the sweet spot for value, resale appeal, and day-to-day enjoyment.
Premium Finish (£2,500–£2,800+/m²)
- Walls: High-spec insulation, premium brick, timber cladding, or render with architectural detailing
- Windows: Aluminium or steel-frame (Crittall-style), triple glazing
- Doors: Large-format aluminium sliding doors (4+ metres), or bespoke timber bi-folds
- Roof: Complex pitched roof with Velux or bespoke rooflights, or a living roof (sedum)
- Flooring: Insulated concrete slab, polished concrete, or premium preparation for natural stone
- Electrics: Smart lighting, integrated AV, separate zone controls
- Plumbing: Wet underfloor heating throughout, separate zone controls, potential heat pump integration
- Decoration: Premium plaster finish, bespoke joinery details
- Suitable for: High-value properties, design-led renovations, or homeowners who plan to stay long-term.
Cost per m² by Extension Size
The size of your rear extension affects the cost per m² in a non-obvious way. Very small and very large extensions both have cost inefficiencies.
| Extension Size | Cost per m² | Why? |
|---|---|---|
| 6–10 m² | £2,200–£3,000 | High fixed costs (foundations, roof, site setup, scaffolding) spread over a small area. Most expensive per m². |
| 11–20 m² | £1,800–£2,500 | The sweet spot. Fixed costs are spread efficiently, and standard construction methods apply. |
| 21–30 m² | £1,700–£2,400 | Economies of scale begin to apply. Larger foundations and roofs are more efficient per m². |
| 30+ m² | £1,700–£2,500+ | Potentially lower per m², but premium finishes, extensive glazing, and complex design often push costs back up. |
Key insight: A 20 m² extension does not cost exactly twice as much per m² as a 10 m² extension. The larger project benefits from economies of scale — the cost of digging foundations, erecting scaffolding, and setting up the site is shared across more floor area.
Cost per m² by Location
Labour and material costs vary significantly across the UK. The table below shows the cost per m² for a mid-range rear extension by region in 2026.
| Region | Cost per m² (mid-range, inc. VAT) | Premium vs. National Average |
|---|---|---|
| London (Zones 1–3) | £2,500–£3,500 | +30–50% |
| London (Outer) | £2,300–£3,200 | +20–30% |
| South East | £2,300–£3,200 | +20–30% |
| South West | £1,900–£2,600 | National average |
| East Anglia | £1,900–£2,600 | National average |
| East Midlands | £1,800–£2,400 | -5–10% |
| West Midlands | £1,800–£2,400 | -5–10% |
| North West | £1,700–£2,300 | -10–15% |
| North East | £1,600–£2,200 | -10–20% |
| Yorkshire & Humber | £1,700–£2,300 | -10–15% |
| Wales | £1,700–£2,400 | -10–15% |
| Scotland | £1,600–£2,300 | -10–20% |
| Northern Ireland | £1,600–£2,200 | -10–20% |
London premium explained: London builders charge more due to higher wages, congestion and parking restrictions, limited access for materials, and higher insurance and compliance costs. A 20 m² rear extension in Clapham or Richmond can cost £55,000–£75,000 all-in, compared to £40,000–£50,000 in Leeds or Manchester.
Suddeco tip: Enter your address on our platform and we'll show you exactly what rear extensions have been approved near you — with real cost data from planning applications. Try it free.
Cost per m² by Extension Type
Not all rear extensions are built the same way. The type you choose has a direct impact on the cost per m².
Single-Storey Rear Extension
The most common type of rear extension — extending straight back from the rear wall.
- Cost per m²: £1,800–£2,800 (inc. VAT)
- Why: Simple rectangular footprint, straightforward foundations, standard roof structure. No complex junctions.
- Best for: Most detached, semi-detached, and end-of-terrace properties with garden space.
Kitchen Rear Extension
A rear extension specifically designed to house a new kitchen or kitchen-diner.
- Cost per m²: £2,000–£3,000 (inc. VAT)
- Why: Additional plumbing, electrics, ventilation, and appliance integration. Typically finished to a higher standard.
- Best for: Homeowners who want an open-plan kitchen-diner with garden access.
- See also: Our dedicated kitchen extension cost per m² guide.
Wrap-Around Extension (Rear + Side Return)
Combines a rear extension with a side return, creating an L-shaped footprint.
- Cost per m²: £2,000–£3,000 (inc. VAT)
- Why: More external wall, more roof area, complex junctions at the corner, and often structural work to open up the existing kitchen.
- Best for: Terraced and semi-detached houses where a rear extension alone would not provide enough width.
- See also: Our side return extension cost guide.
Double-Storey Rear Extension
Extends both the ground floor and the first floor simultaneously.
- Cost per m²: £1,800–£2,500 (inc. VAT)
- Why: The per-m² cost is lower than a single-storey extension because the foundations and roof are spread over two floors. However, the total project cost is significantly higher.
- Best for: Growing families who need both ground floor living space and an extra bedroom or bathroom upstairs.
- See also: Our double-storey extension cost guide.
What Is Included in the per m² Price?
When a builder quotes £2,200 per m², what exactly are you paying for? Here is a typical breakdown of what is included in a standard construction cost per m² for a rear extension in 2026.
Included in the Construction Cost per m²:
- Foundations: Strip or trench fill foundations to a standard depth (typically 1 metre, or deeper if specified by engineer)
- External walls: Cavity walls with insulation, blockwork and brick facing (or rendered block), lintels over openings
- Roof structure: Timber or steel joists, roof covering (tiles, slate, or flat roof membrane), fascias, soffits, and gutters
- Windows and external doors: Standard double glazing, trickle vents, ironmongery
- Internal walls: Stud partitions if required, plasterboard, plaster finish
- Electrical work: First and second fix, including sockets, lighting, and consumer board upgrade if needed
- Plumbing: First and second fix, including hot and cold feeds, waste pipes, and radiator connections
- Floor construction: Concrete slab or suspended floor, insulation, screed or timber floor structure
- Ceiling: Plasterboard ceiling, plaster finish, basic downlights
- Decoration: White emulsion walls and ceilings, undercoat and gloss on woodwork (if included — check with your builder)
- VAT at 20%: Included in the per-m² figures quoted throughout this guide
Sometimes Included (check your quote):
- Floor and wall tiling: Some builders include this in a mid-range quote; others charge extra
- External works: Patio, steps, and drainage connections are often excluded
- Decoration beyond white emulsion: Premium paint finishes may be extra
What Is NOT Included in the per m² Price?
This is where many homeowners get caught out. The per-m² construction cost is only part of the story. Budget separately for the following items, which typically add £500–£1,200 per m² to the all-in cost.
Excluded from the Construction Cost per m²:
| Item | Cost Range (inc. VAT) | Notes |
|---|---|---|
| Kitchen units and appliances | £5,000–£25,000+ | If your extension includes a kitchen. Budget £300–£800 per m² of kitchen space. |
| Tiling (floor and walls) | £1,500–£5,000 | Premium tiles and mosaic work cost more. |
| Worktops | £1,500–£5,000 | Laminate is cheap; quartz, granite, and Dekton are premium. |
| Glazing upgrades | £2,000–£8,000 | Bi-fold doors, sliding doors, roof lanterns, and large windows are extras. |
| Underfloor heating | £1,500–£4,000 | Electric mats are cheaper; wet systems are more expensive but efficient. |
| Structural engineer | £500–£2,000 | Required for all but the simplest extensions. |
| Architect / designer | £3,750–£7,500 | 5–10% of construction cost. |
| Planning permission | £206 / £462 | Householder / full application fees. |
| Building regulations | £200–£1,000 | Local authority or private inspector fees. |
| Party wall surveyor | £700–£2,000 | Required if you share a wall with a neighbour. |
| Site clearance and preparation | £500–£3,000 | Removing old structures, trees, or difficult access. |
| External works (patio, drainage) | £2,000–£8,000 | Connecting drains, laying patios, landscaping. |
| Contingency | 10–15% | Essential buffer for unexpected issues. |
All-in cost per m² (including everything): For a mid-range rear extension, budget £2,500–£3,500 per m² when you include fit-out, fees, and contingency.
How to Calculate Your Total Rear Extension Cost
Follow this step-by-step method to calculate an accurate total cost for your rear extension.
Step 1: Measure Your Proposed Footprint
Measure the external dimensions of your proposed extension. Multiply length by width to get the area in square metres. For an L-shaped wrap-around, calculate each section separately and add them together.
Step 2: Choose Your Location Multiplier
Use the location table above to find your regional cost per m². If you are in London, use the upper end of the range. If you are in the North East or Scotland, use the lower end.
Step 3: Choose Your Finish Level
Decide whether you want budget, mid-range, or premium finishes. Be honest about what you can afford and what will add value to your home.
Step 4: Apply the Formula
Construction cost = Area (m²) × Cost per m² (location + finish)
All-in cost = Construction cost + Fit-out (£5k–£25k if kitchen) + Fees (£4k–£10k) + Contingency (10–15%)
Example Calculation: 20 m² Mid-Range Rear Extension in Manchester
- Area: 20 m²
- Location multiplier: North West (£1,700–£2,300/m²) → use £2,000/m² for mid-range
- Construction cost: 20 × £2,000 = £40,000 (inc. VAT)
- Professional fees: £5,500
- Contingency (12%): £5,460
- Total all-in cost: £50,960
- All-in cost per m²: £50,960 ÷ 20 = £2,548/m²
Example Calculation: 20 m² Mid-Range Rear Extension in London
- Area: 20 m²
- Location multiplier: London (£2,300–£3,200/m²) → use £2,800/m² for mid-range
- Construction cost: 20 × £2,800 = £56,000 (inc. VAT)
- Professional fees: £7,500
- Contingency (12%): £7,620
- Total all-in cost: £71,120
- All-in cost per m²: £71,120 ÷ 20 = £3,556/m²
How to Reduce Your Cost per m²
A lower cost per m² does not have to mean lower quality. Here are proven ways to reduce your cost per m² without cutting corners.
1. Optimise Your Footprint
A simple rectangular shape is the most cost-effective. Every external corner, jog, or bay window adds wall, roof, and foundation cost. Design a shape that maximises internal floor area relative to external perimeter.
2. Build in the Right Season
Builders are quieter in autumn and winter. You may secure a 5–10% discount on labour, and trades are more readily available. The downside is potential weather delays, but a good builder plans for this.
3. Use Standard Materials
Bespoke handmade bricks, imported tiles, and custom steelwork look beautiful but add cost. Standard materials from UK suppliers are cheaper, faster to source, and easier to replace if damaged.
4. Minimise Structural Changes
Avoid knocking down internal load-bearing walls unless essential. If you do need to remove a wall, a steel beam is cheaper than a full structural frame. Keep the existing layout where possible to reduce plumbing and electrical relocation costs.
5. Get Your Design Right First Time
Changes on site are the biggest driver of cost overruns. A detailed, approved set of plans before construction starts eliminates variations and disputes. Our Concept Package delivers detailed plans in 48 hours for £495–£995, potentially saving you thousands in avoidable changes.
6. Choose a Fixed-Price Design Package
Traditional architects charge 5–10% of build cost — £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.
7. Start with a Free Render
Before you spend money on design, get an address-specific cost estimate. Our free render tool analyses nearby approved planning applications and generates an instant cost estimate and 3D visualisation for your property. No credit card required.
Planning Permission & Building Regulations
Permitted Development
Many rear extensions fall under permitted development rights, meaning you do not need full planning permission if you meet these criteria: - Single storey - Maximum depth: 4 m (detached) or 3 m (other houses) from original rear wall - Maximum height: 4 m - 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 are in a conservation area, you will need householder planning permission (£206). The process typically takes 8–12 weeks.
Building Regulations
All rear extensions must comply with Building Regulations, covering: - Structural integrity - Thermal insulation (U-values) - Fire safety - Ventilation - Drainage
You will need either a Building Notice (simpler, less detail) or Full Plans Approval (recommended for extensions). Cost: £200–£1,000 depending on your local authority.
FAQs
What is the average rear extension cost per m² in 2026?
The average cost per m² for a rear extension in the UK in 2026 is £1,800–£2,800 for construction, including VAT at 20%. The all-in cost, including professional fees, contingency, and any kitchen fit-out, is typically £2,500–£3,500 per m².
Why does the cost per m² vary so much?
Cost per m² varies due to location (London is 30–50% more expensive), extension type (wrap-arounds and kitchen extensions cost more), finish level (premium materials cost more), ground conditions (poor soil requires deeper foundations), and the proportion of glazing (bi-fold doors and roof lanterns add cost).
Is a rear extension cheaper per m² than a side return?
Yes. A simple rear extension typically costs £1,800–£2,800 per m², while a side return costs £2,000–£3,000 per m². This is because side returns involve narrow access, complex junctions with existing walls, party wall agreements, and often require rerouting drains and services. However, side returns are usually smaller, so the total cost may be lower.
What is the cheapest cost per m² for a rear extension?
The cheapest rear extensions cost around £1,500–£1,800 per m² in the North of England or Scotland, using basic materials and a simple rectangular footprint. All-in costs at this level are approximately £2,200–£2,700 per m² including fees and contingency.
Does cost per m² go down for larger rear extensions?
Yes, up to a point. Extensions between 15 m² and 25 m² have the most efficient cost per m² because fixed costs (foundations, roof, site setup, scaffolding) are spread over a larger area. Very small extensions (under 10 m²) have a high cost per m² because fixed costs dominate. Very large extensions (30+ m²) may see per-m² costs rise again if premium finishes and glazing are used.
How much does a rear extension cost per m² in London?
In London, a rear extension costs £2,300–£3,500 per m² for construction, depending on zone, finish level, and access constraints. The all-in cost, including fees and contingency, is typically £3,000–£4,500 per m².
What is the most expensive element per m² in a rear extension?
Glazing is typically the most expensive element per m². A square metre of aluminium bi-fold door or roof lantern can cost £1,500–£3,000, compared to £200–£400 for a standard brick wall. Underfloor heating and bespoke kitchens are also significant per-m² cost drivers.
Should I budget for cost per m² or total project cost?
Both. The cost per m² is useful for comparing quotes, benchmarking your project, and evaluating different design options. The total project cost is what you actually need to finance. Always calculate the total cost by multiplying your area by the per-m² rate, then adding fit-out, fees, and contingency.
What does a £2,200 per m² rear extension look like?
At £2,200 per m² (mid-range), you can expect: a single-storey rear extension with a pitched roof or quality flat roof; aluminium or quality uPVC windows; a 3-metre set of aluminium bi-fold or sliding doors; good insulation throughout; plastered walls and ceilings with white emulsion; standard LED lighting; and radiator heating. This is the specification most UK homeowners choose in 2026.
What is the all-in cost per m² for a high-end rear extension?
A high-end rear extension in 2026 has an all-in cost per m² of £3,500–£4,500+. This includes premium construction, extensive glazing, underfloor heating, smart home integration, high-quality finishes, and all professional fees and contingency.
Can I get an accurate cost per m² estimate for my specific address?
Yes. Our free render tool analyses your address and nearby approved planning applications to generate an instant, location-specific cost estimate and 3D visualisation. For a detailed design, upgrade to our Concept Package (£495–£995) for full plans and multiple renders.
How much does a kitchen extension cost per m² compared to a standard rear extension?
Kitchen extensions cost £2,000–£3,000 per m² compared to £1,800–£2,800 per m² for a standard rear extension. The premium comes from plumbing, electrics, appliance integration, ventilation, and typically higher-spec finishes. However, kitchen extensions also add more value to your home. See our kitchen extension cost per m² guide for full details.
Do rear extension prices include VAT?
Yes. All per-m² prices in this guide include VAT at 20% on labour and materials. VAT is charged at 20% on most renovation work in the UK. The only exception is zero-rated VAT for new builds — this does not apply to extensions on existing homes.
Related Articles
- How Much Does a Rear Extension Cost? [2026 Prices]
- Kitchen Extension Cost per m²: The Complete 2026 Guide
- Side Return Extension Cost: 2026 Pricing Guide
- How Much Does a Double-Storey Extension Cost? (2026 UK Guide)
- Suddeco Pricing and Packages
Last updated: 15 January 2026. Cost figures are based on industry data from Checkatrade, the Federation of Master Builders, and the HomeOwners Alliance, adjusted for inflation and 2026 market conditions. All prices include VAT at 20% unless stated otherwise. Cost per m² is an average and actual prices vary by location, specification, and contractor. Always obtain detailed quotes before committing to a project.
See it before you spend a penny
Get a free AI render of your finished project + a real price — in minutes.
Get your free concept →