How Much Does a Rear Extension Cost in 2026? Single vs Double Storey Prices Explained
If you are planning to add space to your home this year, a typical 6m by 4m kitchen extension costing anywhere from £60,000 to £90,000 quickly brings the reality of rear extension cost in 2026 into focus. The headline figures are only part of the story. Prices vary widely depending on size, specification and location, but most UK homeowners are currently paying between £2,200 and £3,500 per square metre for a single storey extension, and slightly less per square metre for a double storey build.
This guide breaks down real world costs, what affects pricing, and how single and double storey extensions compare in terms of value. The aim is to give you a grounded understanding based on how projects are actually priced on site, not just headline figures.
Average Rear Extension Cost in 2026 per Square Metre
Costs remain high in 2026 due to material prices, labour shortages and stricter energy efficiency requirements under current Building Regulations. Most builders price work using per square metre rates, but these figures can be misleading without understanding what sits behind them.
Below is a realistic snapshot for 2026:
| Extension Type | Average Cost per m² | Typical Total Cost |
|---|---|---|
| Single storey rear extension | £2,200 to £3,500 | £35,000 to £90,000+ |
| Double storey rear extension | £1,800 to £3,000 | £60,000 to £150,000+ |
These ranges typically break down as follows:
- Labour, £1,000 to £1,600 per m² depending on region and complexity
- Materials, £1,200 to £1,900 per m² depending on specification
London and the South East often sit at the top end or exceed these ranges by 15 to 25 percent. In the Midlands and North, costs can be closer to £1,800 to £2,500 per m² for straightforward builds.
Per square metre rates usually include the structural shell, insulation, plastering, basic electrics and plumbing. They often exclude kitchens, bathrooms, floor finishes, landscaping, and premium glazing. This is where many budgets fall short.
The per square metre figure for double storey extensions is lower because the foundations and roof are effectively shared across two floors. That said, the overall spend is still higher.
For a deeper look at how pricing is structured across different builds, see How Much Does a House Extension Cost Per Square Metre in 2026? Build Type, Finish Level and Labour Prices Explained.
Example project cost breakdown, 24m² single storey extension
| Item | Typical Cost |
|---|---|
| Groundworks and foundations | £8,000 to £15,000 |
| Structure and brickwork | £10,000 to £18,000 |
| Roofing (flat roof system) | £6,000 to £12,000 |
| Glazing and doors | £5,000 to £20,000 |
| Electrics and plumbing | £4,000 to £8,000 |
| Plastering and internal finishes | £5,000 to £10,000 |
| Kitchen and flooring | £10,000 to £30,000+ |
| Professional fees and design | £3,000 to £8,000 |
| VAT at 20 percent | £10,000 to £18,000 |
Single Storey Rear Extension Costs Explained
A single storey rear extension is the most common type of home improvement project in the UK. It is typically used to create open plan kitchens, dining areas or family rooms.
Typical project cost
For a standard 6m by 4m extension, around 24 square metres:
- Basic specification, £50,000 to £60,000
- Mid range, £60,000 to £75,000
- High specification, £75,000 to £100,000+
These figures include structure, insulation, plastering, electrics and basic finishes. They may not include kitchens, glazing upgrades or landscaping.
Foundations and structure
Most single storey extensions in the UK use trench fill foundations between 1m and 1.5m deep. On clay soils or near trees, depths can increase to 2m or more, adding £5,000 to £15,000 to groundworks.
Steel beams are commonly required when removing the rear wall. A typical RSJ supply and install costs between £1,500 and £3,500 depending on span and access. Larger openings with multiple steels can reach £8,000 or more.
Build time with stages
A typical timeline looks like this:
- Weeks 1 to 3, demolition and foundations
- Weeks 4 to 7, walls and structural shell
- Weeks 8 to 10, roof construction and external doors
- Weeks 11 to 13, first fix electrics and plumbing
- Weeks 14 to 16, plastering and second fix
Weather, material delays and inspections can extend this.
Double Storey Rear Extension Costs Explained
Double storey extensions offer more space per pound but involve greater structural complexity and planning considerations.
Typical project cost
For a similar footprint of 24 square metres per floor:
- Basic specification, £80,000 to £100,000
- Mid range, £100,000 to £130,000
- High specification, £130,000 to £160,000+
Although the total cost is higher, the cost per square metre is usually better value.
Structural considerations
Two storey builds typically require deeper foundations, often 1.5m to 2.5m depending on ground conditions. Additional loading means more concrete, reinforcement and inspections.
Steelwork is also more substantial. Expect £3,000 to £10,000 for structural steels depending on configuration, especially if creating open plan layouts on the ground floor.
- Heavier foundations to support additional load
- More structural steel or load bearing walls
- Additional insulation to meet current thermal standards
- Staircase alterations and internal layout changes
This complexity means you will need detailed drawings and calculations from a structural engineer. In most cases, this is a requirement to gain Building Regulations approval.
Build timeline
- Weeks 1 to 4, groundworks and foundations
- Weeks 5 to 10, full structural shell across both floors
- Weeks 11 to 14, roofing and external envelope
- Weeks 15 to 18, first fix services
- Weeks 19 to 24, second fix and finishing
See more detail here: Planning a Two Storey Extension in the UK Timeline, Key Decisions and Common Hold Ups to Avoid.
What Affects Rear Extension Costs the Most
Every project is different, but builders price using consistent variables.
1. Ground conditions
Poor soil, tree roots or drainage issues can add £5,000 to £15,000 or more. Piling systems can push that even higher.
You can review groundwork safety and standards via the Health and Safety Executive at https://www.hse.gov.uk/construction.
2. Access to site
Restricted access can increase labour costs by 10 to 25 percent due to manual handling and slower progress.
3. Specification level
- Basic aluminium doors, £3,000 to £5,000
- Premium slimline glazing, £10,000 to £20,000+
- Standard kitchen, £8,000 to £15,000
- High end kitchen, £25,000+
4. Structural alterations
Knocking through the rear wall can cost £3,000 to £10,000 depending on steel size, labour and temporary works.
5. Location in the UK
London and the South East are typically 15 to 25 percent higher. Regions in the North East or Wales may be closer to the lower end.
Planning Permission and Building Regulations
Many rear extensions fall under permitted development, but the detail matters. You can check current guidance here: https://www.planningportal.co.uk/permission/common-projects/extensions/planning-permission
For Building Control standards see https://www.labc.co.uk which provides practical guidance used by local authorities.
Permitted development examples
- A 3m rear extension on a semi detached house, usually allowed
- A 6m extension under Prior Approval, subject to neighbour consultation
- Extensions on flats or listed buildings, planning permission required
Prior approval explained
Larger single storey extensions can go beyond standard limits under Prior Approval. This involves submitting details to the council, who consult neighbours. If no objections are raised or concerns resolved, approval is granted.
Party Wall Act
If work affects a shared wall or boundary within 3 metres, you must serve notice under the Party Wall Act. Surveyor costs typically range from £700 to £2,000 per neighbour.
Building Regulations
- Structure under Part A
- Fire safety under Part B
- Energy efficiency under Part L
- Electrical work under Part P, usually via a NICEIC contractor
A structural engineer is required where load bearing changes occur, especially when removing walls or adding floors.
Hidden Costs You Should Budget For
Many projects exceed budget due to overlooked items.
- Temporary accommodation, £1,000 to £3,000 per month if you move out
- Skip hire and waste removal, £1,500 to £3,000
- Utility upgrades such as boilers or consumer units, £2,000 to £6,000
- Snagging and defect correction, often £1,000 to £5,000 post build
Pre build Surveys and Reports Checklist
- Soil or ground investigation survey
- Drainage survey to identify pipe runs
- Asbestos survey for older properties
- Measured building survey for accurate drawings
- Structural assessment where walls are removed
Single vs Double Storey. Which Is Better Value?
| Factor | Single Storey | Double Storey |
|---|---|---|
| Cost per m² | Higher | Lower |
| Total cost | Lower | Higher |
| Added space | Limited | Significant |
| Planning complexity | Usually simpler | More likely to need permission |
| Impact on garden | Same footprint | Same footprint |
Lifecycle value comparison
| Property Type | Single Storey Value Add | Double Storey Value Add |
|---|---|---|
| Terraced house | £30,000 to £60,000 | £60,000 to £100,000 |
| Semi detached | £40,000 to £80,000 | £80,000 to £140,000 |
| Detached | £50,000 to £100,000 | £100,000 to £200,000+ |
Extend vs Move. Cost and Value Comparison
| Factor | Extend | Move House |
|---|---|---|
| Upfront cost | £60,000 to £150,000 | Stamp duty plus fees often £20,000+ |
| Disruption | High during build | One off move |
| Added value | Can exceed build cost | Depends on market |
| Customisation | Fully tailored | Limited |
Example Project Case Study
A recent project in the Midlands involved a 5m by 4.5m rear extension with bifold doors and a kitchen install.
- Build cost, £68,000
- Kitchen and finishes, £18,000
- Professional fees, £5,000
- Total including VAT, £109,000
- Timeline, 14 weeks on site
The property value increased by approximately £95,000 based on local comparables, making it a strong long term investment.
Common Mistakes to Avoid
Underestimating the total cost
This can add £10,000 or more in late upgrades and redesign.
Skipping detailed drawings
Leads to inaccurate quotes and variation costs that can easily exceed £5,000 to £15,000.
Choosing the cheapest quote
Often results in missing items and mid project cost increases.
Poor project sequencing
Delays can add weeks of labour costs and extend hire of scaffolding and skips.
Ignoring drainage and services
Unexpected drainage works can add £3,000 to £10,000.
How to Get Accurate Quotes
The best quotes come from clear information. Builders often price competitively upfront, then rely on variations if details are vague. A thorough specification protects your budget.
- Full drawings and structural details
- Detailed finishes specification
- Access and logistics explained
- Clear timeline expectations
Expect detailed quotes to take one to three weeks to prepare.
For a broader overview of extension pricing and planning considerations, see Extension cost breakdown and planning advice.
FAQs
How much does a 5m rear extension cost in 2026?
A 5m rear extension typically costs between £60,000 and £100,000. Wider properties or high specification finishes can push this beyond £120,000. Structural steel and glazing are common cost drivers.
Is a double storey extension cheaper than building two single extensions?
Yes. Combining the work saves on duplicated foundations and roofing. Doing the work in phases can add 20 to 30 percent overall.
Do I always need planning permission for a rear extension?
No. Many fall under permitted development, but larger schemes, flats and listed buildings require full approval.
How long does a rear extension take to build?
Single storey builds take around 10 to 16 weeks. Double storey builds take 16 to 24 weeks. Design and approvals can add several months.
Will an extension add value to my home?
In most UK areas, yes. Kitchens and extra bedrooms provide the strongest returns, but always check local ceiling values.
Can you reclaim VAT on a rear extension?
No. VAT at 20 percent applies to most extension work. Reclaim schemes are generally limited to new builds or qualifying conversions.
How can I reduce rear extension costs without lowering quality?
Keep the design simple, avoid excessive glazing, use standard materials and finalise specifications early. Good planning reduces costly changes during the build.
Final Thoughts
Rear extension costs in 2026 remain significant, but they reflect stricter regulations, improved energy performance and the reality of skilled labour demand. A well planned project with clear costs upfront will avoid most of the common pitfalls.
If you are ready to move forward, the simplest way to get started is to post a job on BookaBuilderUK and receive free quotes from vetted local tradespeople who can price your project properly and carry it through to completion.
