architects FROM LONDON

Extension Cost London

How Much Does a House Extension Cost in London?

↓

RIBA Chartered

Award winning

London · Vienna · Rome

Featured in The Times

Panel at Grand Designs Live

Extension Cost London intro

How Much Does a House Extension Cost in London?

Building an extension in London generally costs more than carrying out an equivalent project elsewhere in the UK.

Higher prices can reflect:

Labour rates
Contractor demand
Restricted site access
Parking and delivery constraints
Waste removal
Scaffolding
More complicated logistics
Party-wall matters
Higher specification expectations

Across the UK, a typical completed house extension currently costs around £1,800–£3,000 per m². Federation of Master Builders guidance notes that London and South East extension costs can be around 30–50% higher per square metre than the national average. FMB

For early London budgeting, this means approximately £2,300–£4,500 per m² can be a useful broad starting range, with complex, highly specified or difficult-access projects capable of exceeding it.

For some types of London extension, particularly side returns, current Checkatrade guidance specifically reports costs of up to around £4,500 per m².

At Tholos Architects, we help homeowners develop extensions around the property, planning constraints and available budget rather than designing first and discovering the London construction cost later.

Extension Cost London explained

London Extension Cost per Square Metre

For 2026, a useful broad budgeting guide is:

These are early budgeting figures rather than quotations.

The national benchmark remains around £1,800–£3,000 per m², while FMB notes London and South East costs can be 30–50% higher because of location, labour and logistics.

Typical London Extension Costs by Size

Using a broad London budgeting range of approximately £2,300–£4,500 per m²:

Extension Size	Indicative London Construction Cost
15 m²	£34,500–£67,500
20 m²	£46,000–£90,000
25 m²	£57,500–£112,500
30 m²	£69,000–£135,000
40 m²	£92,000–£180,000
50 m²	£115,000–£225,000

These figures are intended for early budgeting only.

The final project budget may also need to include:

Architectural services
Structural engineer
Planning
Building Control
Party-wall surveyors
Kitchen
Bathrooms
External works
VAT
Contingency

Why Extensions Cost More in London

The bricks and concrete are not necessarily fundamentally different in London.

Much of the additional cost comes from the environment in which the project is being delivered.

London projects frequently involve:

Higher labour costs
Limited contractor availability
Congested roads
Parking restrictions
Difficult deliveries
Restricted rear access
Permit costs
More expensive waste removal
More complicated scaffolding

FMB specifically identifies London and the South East as higher-cost regions and notes that urban sites with difficult access and restricted parking can increase extension costs further.

London Labour Costs

Labour is one of the major reasons London projects cost more.

A construction project can involve:

Groundworkers
Bricklayers
Carpenters
Roofers
Electricians
Plumbers
Plasterers
Decorators

Higher trade rates become particularly significant on labour-intensive projects.

A complicated extension involving months of work therefore experiences the London premium far more than simply the material cost of the new floor area.

Restricted Access Costs

Many London properties are:

Materials may therefore need to be:

Excavated soil and demolition waste may need to leave by the same restricted route.

This can increase labour considerably.

Parking and Delivery Costs

Parking can become a real project expense.

Contractors and suppliers may need:

A delivery that takes 20 minutes on an open suburban site may take considerably longer on a congested London street.

Those logistical costs ultimately affect the project price.

Waste Removal in London

Waste removal can also be more difficult.

A conventional skip may not always be practical where:

Alternative arrangements can include:

This can increase both labour and disposal costs.

Double-storey Extension Cost

Single-storey Extension Cost London

Single-storey extensions are common across London.

They may create:

The UK-wide benchmark for single-storey extensions is around £1,800–£3,000 per m², but FMB reports London and South East costs can be around 30–50% higher.

For London, a realistic early budget may therefore fall broadly around:

£2,300–£4,500 per m²

depending on specification, access and complexity.

Single-storey Extension Cost

↓

20 m² Extension Cost London

For a 20 m² London extension, a broad early construction budget might be approximately:

£46,000–£90,000

This is based on the wider London budgeting range rather than a fixed contractor price.

The cost could rise further where the project includes:

30 m² Extension Cost London

For approximately 30 m²:

£69,000–£135,000

is a useful broad London construction allowance.

A project at the lower end would need to remain relatively straightforward.

A complex kitchen extension with extensive structural remodelling could move toward or beyond the upper end.

40 m² Extension Cost London

A 40 m² extension might broadly require:

£92,000–£180,000

for construction.

At this scale, specification becomes increasingly important.

The difference between:

and:

can easily amount to tens of thousands of pounds.

50 m² Extension Cost London

At approximately 50 m², early London budgeting might sit around:

£115,000–£225,000

depending on the design.

Larger projects can sometimes provide better value per square metre because fixed site costs are distributed across a greater floor area.

However, premium specification can quickly remove that advantage.

Rear Extension Cost London

Rear extensions are one of the most common ways to enlarge a London property.

They are often used to create:

The cost depends heavily on:

Terraced houses can be particularly expensive where all labour, materials and waste need to pass through the property.

Side-return Extension Cost London

Side-return extensions are especially common on Victorian and Edwardian London houses.

Current Checkatrade guidance gives approximately:

£1,500–£3,000 per m² outside London

but up to around £4,500 per m² in London. Checkatrade

That higher London rate reflects the fact that even a relatively small side return may involve:

Side-return Extension Cost

↓

Wraparound Extension Cost London

A wraparound extension combines rear and side extension space.

It can create a much larger ground floor but also involves more:

In London, a wraparound project can therefore sit toward the upper end of extension cost ranges, particularly where it transforms the entire ground floor.

Wraparound Extension Cost

↓

Kitchen Extension Cost London

Kitchen extensions can be significantly more expensive than basic room extensions because the budget needs to include both:

the building

and

the kitchen itself.

Current FMB guidance states that a London single-storey kitchen extension starts around £1,700 per m², while also stressing that the final price varies considerably with structural steel, glazing, ground conditions and finish.

In practice, completed projects can cost considerably more once a full kitchen specification and substantial structural alteration are included.

Kitchen Extension Cost

↓

Double-storey Extension Cost London

A double-storey extension costs more overall but can provide better value per square metre because both floors share:

Current UK guidance puts double-storey extensions around £1,650–£3,000 per m², depending on quality and location.

London labour and logistics can push a project above typical national levels.

Double-storey Extension Cost

↓

London Terraced House Extension Cost

Terraced houses are particularly common in London.

They can also present some of the most difficult construction logistics.

Typical challenges include:

No side access
Materials carried through the house
Waste carried through the house
Party walls on both sides
Limited scaffold access
Controlled parking

Nationally, Checkatrade gives around £30,000–£42,000 for a small 15 m² rear terraced-house extension and £60,000–£84,000 for a 30 m² version, before allowing for the higher costs commonly experienced in London.

A London terraced project may therefore cost substantially more.

Victorian House Extension Cost London

Victorian homes provide many opportunities for:

But they can also introduce additional uncertainty.

Common issues include:

A larger contingency may therefore be sensible.

Edwardian House Extension Cost London

Edwardian homes can have similar opportunities.

Their larger plots and wider side passages may allow more generous extensions, but costs can still be affected by:

The existing property should be assessed rather than assuming every period house behaves the same way.

Semi-detached Extension Cost London

Semi-detached houses may provide easier side access than terraced homes.

That can help reduce some logistical costs.

However, the final price still depends on:

Current national guidance places semi-detached extensions around £1,800–£3,000 per m², before London’s regional premium is considered.

Structural Work in London Extensions

Many London extensions are not simply new rooms attached to the house.

They involve opening the original property to create:

This can require:

The larger the opening, the more expensive the structural solution can become.

extension cost in London

Removing the Rear Wall

A large rear opening may require substantial steelwork to support:

This can become one of the largest construction costs in the project.

Before assuming that the entire wall needs to disappear, consider whether a slightly smaller opening or carefully positioned column could achieve the same practical result at lower cost.

Structural Engineer Costs

Structural engineering is normally additional to the construction quotation unless expressly included.

Engineering may be required for:

Structural Engineer Cost

↓

Foundation Costs in London

Foundation costs depend on:

London contains varying ground conditions, and individual properties need to be assessed on their own merits.

Foundation cost can increase unexpectedly where excavation reveals conditions different from those anticipated during pricing.

Drainage Costs

London side-return and rear extensions frequently encounter existing drainage.

The footprint may contain:

Work may require:

Investigating drainage early can reduce uncertainty.

Party Wall Costs in London

Party-wall considerations are particularly common because London properties are often closely spaced.

They may arise from:

Surveyor costs can therefore form part of the project budget.

They should not automatically be assumed to be included in architectural or construction fees.

Basement and Existing Structures

Some London homes contain:

These can affect the structural design of a new extension.
Where existing construction is uncertain, additional investigation may be required.

Glazing Costs

Large glazed doors are extremely popular in London extensions.

Options include:

Large openings can affect both:

A premium glazing package can add tens of thousands of pounds.

Rooflights

Rooflights can be an efficient way to bring natural light into deeper extension plans.

This is particularly useful for:

Standard rooflights generally cost less than bespoke structural glazing.

Kitchen Costs

A new kitchen can form a substantial part of the overall London extension budget.

The final cost depends on:

A builder’s construction quotation may include only an allowance for the kitchen, or may exclude it entirely.

Always check.

extension cost in London

Internal Remodelling Costs

A London extension frequently triggers changes to the existing house.

These may include:

These costs do not increase the extension’s square metre figure but they still increase the total project budget.

Internal Remodelling

↓

Open-plan Extension Costs

Open-plan design can require substantial structural alteration.

A more modest opening may cost significantly less than completely removing:

The structural strategy should therefore be part of the early cost conversation.

Open-plan Living

↓

Planning Permission for London Extensions

Whether planning permission is required depends on the specific:

Some extensions may fall within permitted development rights.

Others require a householder planning application.

London properties may also be affected by:

The position should therefore be checked for the individual property.

Planning Permission

↓

London Conservation Area Extension Costs

London contains many conservation areas.

A conservation-area project may involve additional work around:

This can affect both professional fees and construction specification.

Conservation Area Planning

↓

Building Regulations

Applicable Building Regulations requirements normally apply regardless of whether the extension needs planning permission.

They can cover areas including:

Building Regulations

↓

Architectural Drawing Costs

Architectural fees should also form part of the project budget.

The drawings may include:

Architectural Drawings Cost

↓

VAT

Always establish whether the extension prices being compared include VAT.

Checkatrade’s national extension examples, for example, specifically present several headline cost ranges excluding VAT.

That distinction is crucial.

A £100,000 figure excluding VAT does not represent the same homeowner budget as £100,000 including VAT.

Extension cost in London

Hidden London Extension Costs

Potential additional costs can include:

Parking suspensions
Scaffold permits
Skip permits
Party-wall surveyors
Temporary accommodation
Storage
Utility alterations
Waste disposal
Landscaping
- VAT

These should be considered before treating the builder’s quotation as the entire budget.

Hidden Building Costs

↓

Project Contingency

London construction projects should also retain contingency.

Around 10% is a useful starting point for many well-defined projects.

Older period properties, extensive structural alterations or projects with more uncertainty may justify 15% or more.

extension cost in London

Can You Build a London Extension for £50,000?

Possibly, but expectations need to be realistic.

At a broad London range of approximately £2,300–£4,500 per m², £50,000 broadly represents around:

before separately adding expensive kitchens, professional fees and other excluded items.
A relatively simple small extension may therefore be achievable.

A substantial high-spec kitchen extension is unlikely to fit comfortably within the same budget.

Can You Build a London Extension for £75,000?

Yes, depending on size and specification.

£75,000 could support a modest London extension where:

A complex side-return or high-spec project could still exceed this level.

Can You Build a London Extension for £100,000?

A £100,000 construction budget can deliver a meaningful extension in many London properties.

However, the total project budget may need to exceed £100,000 once you include:

The difference between construction budget and total project budget is particularly important.

Can You Build a London Extension for £150,000?

Yes.

At £150,000 there is significantly more flexibility for:

But complex wraparound schemes or extensive renovation combined with an extension can still exceed this amount.

Can a London Extension Cost £200,000 or More?

Absolutely.

A larger London project can exceed £200,000 where it combines:

The cost-per-square-metre benchmark should therefore never be treated as a maximum.

extension cost in London

How to Reduce Extension Costs in London

Some of the most effective savings come from design rather than choosing cheaper finishes at the end.

Possible strategies include:

Keep the footprint efficient
Simplify structural openings
Use standard glazing sizes
Keep the roof simple
Limit service relocation
Investigate drainage early
Avoid unnecessary demolition
Control specification before tender

Build Less, Design Better

When London construction costs are high, adding every possible square metre may not make sense.

Sometimes a smaller extension combined with:

can produce a much better result than simply maximising floor area.

A 25 m² extension that works brilliantly may represent better value than a poorly organised 35 m² extension.

Simplify the Structure

One carefully positioned column can sometimes avoid:

The architectural and structural design should therefore be developed together.

Simplify the Roof

Complex roofs increase:

A well-designed simple roof can still create an excellent architectural result.

Control Glazing Early

Large glazing is visually appealing but can affect:

Decide early where premium glazing genuinely adds value.

Design the Kitchen Before Finalising the Extension

Do not determine the extension size first and then try to fit the kitchen into it.

Consider:

while the architectural layout is still being developed.

You may discover that less floor area is actually required.

Get Detailed Builder Quotes

Given London’s construction costs, quotation differences can become very large.

Builders should ideally price the same:

Otherwise, an apparently cheap quote may simply contain more exclusions.

Check a Builder Quote

↓

Do Not Choose the Cheapest London Builder Automatically

London construction is expensive, so a very low quotation can be attractive.

But check:

A cheaper starting quote can become considerably more expensive after variations.

Check a Builder Quote

↓

extension cost in London

London Extension Budget Checklist

Your complete project budget may need to include:

Construction
Demolition
Foundations
Structural steel
Drainage
Roof
Glazing
Kitchen
Electrical work
Plumbing
Heating
Flooring
Decoration
Architectural fees
Structural engineer
Planning
Building Control
Party-wall surveyors
Parking and permits
Scaffolding
Waste disposal
External works
VAT
Contingency

Do not assume the price per square metre covers every one of these items.

How Tholos Can Help Control London Extension Costs

London extension costs make early design decisions particularly important.

At Tholos Architects, we can consider:

Floor area
Existing layout
Structure
Roof
Glazing
Planning
Access
Kitchen
Budget

together.

The objective is not simply to make the extension smaller.

It is to ensure that the money being spent creates useful space rather than unnecessary structural or construction complexity.

Client experience

"

Lorem ipsum dolor sit amet, consectetur adipiscing elit. We had a vision for our home but no idea how to realise it. Tholos Interiors took complete ownership of the project — every detail was considered, every decision explained. The result exceeded everything we had imagined.

– Lawrence Ipsum, Homeowner · London –

Frequently Asked Questions

How much does an extension cost in London per m²?

A useful 2026 early budgeting range is approximately £2,300–£4,500 per m², depending on the project. This reflects national extension costs of around £1,800–£3,000 per m² and FMB guidance that London and South East projects can cost approximately 30–50% more per square metre.

How much does a 20 m² extension cost in London?

A broad early-stage budget is approximately £46,000–£90,000 for construction, depending on specification and complexity.

How much does a 30 m² London extension cost?

Approximately £69,000–£135,000 is a useful broad early allowance.

How much does a London side-return extension cost?

Current Checkatrade guidance suggests side-return extensions can reach approximately £4,500 per m² in London

Is £100,000 enough for a London extension?

It can be, depending on size, structure and specification. Remember that the total project budget may also need to cover professional fees, approvals, VAT and contingency.

Budget for London, Not the National Average

One of the easiest ways to underestimate an extension is to find a national price-per-square-metre figure and apply it directly to a London property.

Current UK extension guidance sits around:

£1,800–£3,000 per m²

but London and South East projects can cost around 30–50% more per square metre according to FMB. FMB

For early London planning, approximately:

£2,300–£4,500 per m²

is therefore a more useful broad budgeting range, with particularly complex projects capable of costing more.

The right figure depends on the actual property, access, design, structure and specification.

At Tholos Architects, we can help develop an extension around both what you want to achieve and what is realistic for your London project budget.

Disclaimer

This article is part of a series created by our dynamic marketing team for informational purposes only. While we strive to review all content thoroughly, occasional oversights may occur, even after publication. Therefore, we cannot accept liability for any interpretations or use of the information provided. For the most up-to-date information or to report any discrepancies, please contact us at hello@tholos-architects.com.

Start your project

Extension Cost London

How Much Does a House Extension Cost in London?

How Much Does a House Extension Cost in London?

London Extension Cost per Square Metre

Typical London Extension Costs by Size

Why Extensions Cost More in London

London Labour Costs

Restricted Access Costs

Parking and Delivery Costs

Waste Removal in London

Single-storey Extension Cost London

20 m² Extension Cost London

30 m² Extension Cost London

40 m² Extension Cost London

50 m² Extension Cost London

Rear Extension Cost London

Side-return Extension Cost London

Wraparound Extension Cost London

Kitchen Extension Cost London

Double-storey Extension Cost London

London Terraced House Extension Cost

Victorian House Extension Cost London

Edwardian House Extension Cost London

Semi-detached Extension Cost London

Structural Work in London Extensions

Removing the Rear Wall

Structural Engineer Costs

Foundation Costs in London

Drainage Costs

Party Wall Costs in London

Basement and Existing Structures

Glazing Costs

Rooflights

Kitchen Costs

Internal Remodelling Costs

Open-plan Extension Costs

Planning Permission for London Extensions

London Conservation Area Extension Costs

Building Regulations

Architectural Drawing Costs

VAT

Hidden London Extension Costs

Project Contingency

Can You Build a London Extension for £50,000?

Can You Build a London Extension for £75,000?

Can You Build a London Extension for £100,000?

Can You Build a London Extension for £150,000?

Can a London Extension Cost £200,000 or More?

How to Reduce Extension Costs in London

Build Less, Design Better

Simplify the Structure

Simplify the Roof

Control Glazing Early

Design the Kitchen Before Finalising the Extension

Get Detailed Builder Quotes

Do Not Choose the Cheapest London Builder Automatically

London Extension Budget Checklist

How Tholos Can Help Control London Extension Costs

"

Book a free design consultation