How Much Does a House Extension Cost in the UK? (Rear, Side & Wraparound) (2026 Price Guide)

How Much Does a House Extension Cost in the UK?

House extension costs vary significantly depending on type, size, specification, and structural complexity.

Average UK extension costs:

• Rear extension: £1,800 – £3,000 per m²
• Side extension: £1,900 – £3,200 per m²
• Wraparound extension: £2,200 – £3,500+ per m²

Typical total extension costs:

• Small rear extension: £40,000 – £70,000
• Medium extension: £70,000 – £120,000
• Large wraparound extension: £120,000 – £200,000+

Extension Cost Per m² (UK Breakdown)

Typical installed costs per m²:

• Basic extension (standard finish): £1,800 – £2,200 per m²
• Mid-range extension: £2,200 – £2,800 per m²
• High-end extension: £2,800 – £3,500+ per m²

Wraparound extensions tend to sit at the higher end due to structural complexity and additional steelwork.

Rear Extension Costs

Rear extensions are the most common type in the UK.

Typical rear extension cost:

• £1,800 – £3,000 per m²

What affects rear extension cost:

• Size and footprint
• Bi-fold or sliding doors
• Steel beam requirements
• Ground conditions
• Whether it includes a kitchen/dining space

Example:

• 20m² rear extension
• £2,200 per m² average
• Total: £44,000

Rear extensions are generally the most cost-efficient type due to simpler structure and easier access.

Side Extension Costs

Side extensions are common for semi-detached and detached homes.

Typical side extension cost:

• £1,900 – £3,200 per m²

Why side extensions can cost more:

• Restricted access for machinery
• Boundary constraints
• Drainage diversions
• More complex foundations in narrow spaces

Example:

• 25m² side extension
• £2,400 per m² average
• Total: £60,000

Side extensions often require careful planning due to boundary and access limitations.

Wraparound Extension Costs

Wraparound extensions combine rear and side extensions into an L-shaped structure.

Typical wraparound extension cost:

• £2,200 – £3,500+ per m²

Why they cost more:

• Higher steel requirement
• Complex structural engineering
• More groundworks and foundations
• Larger roof structure
• Increased design and coordination complexity

Example:

• 40m² wraparound extension
• £2,800 per m² average
• Total: £112,000

Wraparound extensions deliver the most space but are structurally the most complex.

What Affects Extension Costs?

1. Structural Steelwork

Most extensions require steel beams (RSJs):

• Small beams: £500 – £1,500
• Large structural frames: £2,000 – £8,000+

Steel design complexity significantly affects cost.

2. Foundations and Groundworks

Ground conditions heavily influence pricing:

• Standard strip foundations: £5,000 – £15,000
• Poor ground / reinforcement required: £10,000 – £25,000+

3. Glazing and Doors

Large openings increase cost:

• Bi-fold doors: £2,000 – £8,000+
• Sliding glass systems: £3,000 – £10,000+
• Roof lanterns: £1,000 – £4,000+

4. Roof Type

Roofing choices impact overall budget:

• Flat roof (EPDM/felt/GRP): most cost-effective
• Pitched roof: higher labour and materials
• Lantern or vaulted ceilings: premium cost

5. Internal Finish Level

Internal works can significantly increase costs:

• Basic finish: £10,000 – £20,000
• Mid-range finish: £20,000 – £40,000
• High-end finish: £40,000 – £80,000+

Includes:

• Plastering
• Electrics
• Plumbing
• Flooring
• Kitchen installation (if applicable)

Labour Costs for House Extensions

Labour typically accounts for 35%–55% of total cost.

Typical daily rates:

• General builder: £180 – £300 per day
• Bricklayer: £200 – £350 per day
• Carpenter: £200 – £350 per day
• Electrician: £200 – £400 per day
• Plumber: £200 – £400 per day

Typical build duration:

• Rear extension: 8–12 weeks
• Side extension: 10–14 weeks
• Wraparound extension: 12–20+ weeks

Example Extension Costs

Small Rear Extension (15–20m²)

• Build cost: £30,000 – £50,000
• Internal finishes: £10,000 – £20,000
• Total: £40,000 – £70,000

Medium Side Extension (20–30m²)

• Build cost: £40,000 – £70,000
• Internal finishes: £15,000 – £30,000
• Total: £60,000 – £100,000

Large Wraparound Extension (35–60m²)

• Build cost: £80,000 – £140,000
• Internal finishes: £30,000 – £60,000
• Total: £120,000 – £200,000+

Hidden Costs in House Extensions

Common additional costs include:

• Planning permission & drawings: £2,000 – £6,000
• Building regulations approval: £1,000 – £3,000
• Party wall agreements: £700 – £2,000
• Drainage diversions: £1,000 – £5,000
• Utility connections: £500 – £3,000
• Landscaping after build: £1,000 – £10,000+

Regional Price Differences in the UK

• London & South East: 10%–30% higher
• Midlands: standard UK pricing
• North of England: slightly lower labour rates
• Rural areas: higher logistics and access costs

How Long Does a House Extension Take?

• Rear extension: 2–3 months
• Side extension: 3–4 months
• Wraparound extension: 4–6+ months

Delays are often caused by weather, inspections, or material lead times.

Types of House Extensions

Rear Extension

• Most common
• Best cost-to-space ratio
• Ideal for kitchens/dining areas

Side Extension

• Uses unused side space
• Often subject to boundary constraints

Wraparound Extension

• Combines rear and side
• Maximises ground floor space
• Highest cost but biggest transformation

How to Get an Accurate Extension Quote

To avoid inaccurate pricing, contractors should:

• Measure exact footprint and m²
• Confirm structural design early
• Include steelwork allowances
• Check ground conditions properly
• Price labour realistically over full timeline
• Include planning and compliance costs
• Allow for contingencies (10–15%)

Extensions are one of the most underquoted construction jobs due to hidden structural and compliance costs.

How Pricing Penguin Helps Contractors

Customers often don’t have a clear understanding of what a construction job should cost before they speak to a tradesperson. As a result, many enquiries come in “cold” — with unrealistic expectations, mismatched budgets, or purely price-driven intent. This leads to wasted time quoting jobs that were never viable in the first place.

Pricing Penguin changes that dynamic by giving customers a realistic, data-driven price range before they ever pick up the phone or submit an enquiry.

Instead of guessing or waiting for a contractor to explain costs after the fact, customers can immediately understand:

• What their type of job typically costs in their area
• What drives the price up or down (size, materials, complexity, access, etc.)
• Whether their budget is realistically aligned with the work they want done

This creates a pre-qualified customer before the first interaction even happens.

For contractors, this means fewer wasted site visits, fewer unrealistic enquiries, and a much higher proportion of leads that are actually ready to proceed. Rather than spending time filtering out low-quality leads, tradespeople can focus on quoting and winning work that already fits their pricing structure.

In short, Pricing Penguin acts as a pricing filter between customer expectation and real-world construction costs — improving conversion quality, saving time, and helping contractors focus on profitable work instead of time-wasting enquiries.

FAQ

How much does a rear extension cost in the UK?

Typically £1,800 – £3,000 per m² or £40,000 – £70,000 total.

What is the cheapest type of extension?

A simple rear extension with standard finishes and flat roof.

What is the most expensive extension type?

Wraparound extensions due to structural complexity and size.

Does a house extension add value?

Yes — well-designed extensions often add significant property value and usability.

Conclusion

House extensions in the UK typically cost between £1,800 and £3,500 per m² depending on type and specification.

Rear extensions offer the best value, side extensions require more planning, and wraparound extensions provide maximum space but at the highest cost.

For homeowners, understanding cost drivers prevents budget surprises.

For contractors, accurate estimating is essential to protect profit and win profitable work.

Better pricing leads to better projects — and stronger construction businesses.