How Much Does a House Extension Cost in Surrey in 2026?

Thinking about extending your home in Surrey? A house extension can be one of the most effective ways to create more living space without moving, but understanding the likely cost before you start is essential.

In 2026, a typical single-storey house extension in Surrey can cost roughly £2,700–£3,600 per square metre for the construction work, with the final figure depending heavily on the size, structure, access, specification and level of finish.

For a homeowner, that means a straightforward 20m² extension might realistically fall around £60,000–£90,000, while a larger or higher-specification 30m² extension can easily reach £85,000–£120,000 or more once VAT, professional fees, approvals and contingency are taken into account.

A kitchen, premium glazing, complicated structural work or difficult ground conditions can push the cost considerably higher.

These are planning figures, not quotes. Every property is different, and the final cost should always be established from drawings, a defined specification and competitive written quotations. For a shorter national overview, see the average cost of a home extension in the UK.

The average cost of a house extension in Surrey

There is no single average price for an extension, because two projects of exactly the same size can have completely different specifications.

A useful national benchmark from Homebuilding & Renovating puts a typical single-storey extension at approximately £2,200–£3,300 per m² excluding VAT, with higher-end specifications at the top of that range. The publication also notes that London and the South East can command a significant regional premium.

For Surrey homeowners, using the national average without allowing for regional conditions can therefore produce an unrealistically low budget.

As a practical 2026 planning allowance, consider:

*Construction cost is a broad working estimate and will vary by specification, contractor and site.

**Homeowner budget is a more realistic allowance including typical professional fees, approvals and contingency. It excludes major furniture purchases and exceptional site problems.

For comparison, Checkatrade's house extension guide places a completed extension at around £1,800–£3,000 per m², while Homebuilding & Renovating gives £2,200–£3,300 per m² for a single-storey extension depending on quality and complexity. The gap between published guides is why a homeowner should treat online averages as a starting point rather than a quotation.

Why are extensions more expensive in Surrey?

Surrey is not one uniform construction market. The cost of extending a property in Woking, Guildford, Cobham, Weybridge or Esher can differ substantially because property types, land values, access, planning constraints and specification expectations all vary.

The wider housing market shows how different the local areas can be. The UK House Price Index for July 2026 puts the average Surrey property price at approximately £522,500.

There is significant variation within Surrey itself:

• Woking: approximately £440,000
• Guildford: approximately £533,000
• Waverley: approximately £553,000
• Epsom and Ewell: approximately £568,000

These figures are not extension prices. They show how different the property markets are across the county.

For an extension, regional pricing is also affected by labour availability, contractor demand, site access and the specification expected locally. Homebuilding & Renovating identifies location, access, ground conditions and specification as major variables, and notes a significant South East premium.

What does a typical Surrey extension actually cost?

The easiest way to think about an extension budget is to start with the new floor area, then adjust for the type of project.

1. Small single-storey rear extension: £55,000–£85,000

A relatively simple 15–20m² rear extension can be one of the more straightforward ways of adding space.

A 4m × 5m extension could create enough room for a larger dining area, family room or expanded kitchen.

The cost rises quickly when you introduce:

• large areas of glazing
• aluminium bifold or sliding doors
• roof lanterns or multiple rooflights
• complicated roof designs
• structural openings into the existing house
• premium flooring
• underfloor heating
• upgraded electrical installations
• a new kitchen

A simple extension with standard windows and finishes will sit towards the lower end of the range. A highly glazed architectural extension can move towards or beyond the upper end.

2. Kitchen extension: £85,000–£145,000+

Kitchen extensions are often considerably more expensive than homeowners initially expect.

The building itself may be relatively straightforward, but the extension becomes the framework for a new kitchen.

In addition to the structural build, you may need to budget for:

• kitchen units
• worktops
• an island
• appliances
• plumbing
• electrical upgrades
• lighting
• extraction
• heating
• flooring
• decoration
• structural alterations to the existing kitchen
• relocation of boilers or services

Checkatrade's extension guide estimates that a kitchen can add approximately £15,000–£35,000, depending on the installation.

A £70,000 building project can therefore become a £100,000+ project once the kitchen and associated finishing work are included. This is one of the most common reasons homeowners underestimate extension costs.

3. Side-return extension: £45,000–£80,000

Side-return extensions are particularly common on Victorian and Edwardian terraced homes.

They typically extend into the narrow side passage beside the house, often creating a more practical kitchen and dining space.

Although a side return may be relatively small, it can cost more per square metre than a simple rear extension. Builders may be working in restricted access, dealing with existing walls, drainage, neighbouring structures and awkward connections to the original building.

Homebuilding & Renovating puts typical side-return costs at approximately £2,800–£3,100 per m² before higher specifications and regional premiums are applied.

In Surrey, a smaller extension does not automatically mean a proportionally cheaper project.

4. Wraparound extension: £110,000–£180,000+

A wraparound extension combines a rear and side extension to create a much larger footprint.

It can transform the ground floor of a property, particularly where the existing kitchen, dining and living spaces are disconnected.

The project can involve:

• significantly more foundations
• multiple structural connections
• extensive roof work
• substantial drainage changes
• larger areas of glazing
• removal of existing walls
• extensive landscaping afterwards

For a 30–50m² project, a Surrey homeowner should realistically consider a six-figure budget once construction, professional fees, VAT, finishes and contingency are included.

5. Two-storey extension: £90,000–£160,000+

A two-storey extension looks expensive because you are building twice the floor area, but the cost per square metre can be lower than building two separate single-storey structures. The foundations, external walls and some structural elements serve both floors.

Homebuilding & Renovating estimates approximately £2,000–£3,200 per m² for two-storey extensions, depending on specification.

A two-storey extension can therefore be an efficient way of adding substantial space, particularly if you need both an enlarged ground floor and extra bedrooms or bathrooms upstairs.

Planning, structural engineering, roofing and integration with the existing house can become considerably more complicated.

6. Extension over a garage or first-floor extension: £55,000–£95,000

Building above an existing garage can look relatively simple. Whether it is economical depends on how the existing structure was designed.

The garage may not have been built to support another storey, so additional structural work or new foundations may be required.

Checkatrade's benchmark places a 25m² first-floor extension at approximately £45,000–£75,000, before more expensive finishes or challenging structural conditions.

7. Glass extensions, orangeries and premium structures

The word "extension" covers a huge range of construction types.

A basic insulated masonry extension is very different from a highly glazed room with structural glass and aluminium framing.

Checkatrade's glass extension guide puts the average glass extension at around £3,000+ per m², with typical projects around £43,000 and premium projects reaching substantially higher figures.

The materials alone can change the price dramatically.

The more glass, bespoke joinery and architectural detailing you introduce, the less useful a generic £/m² estimate becomes.

Where does the money actually go?

Homeowners often look at an extension quote as one large figure. Understanding the components is more useful.

A typical project can be divided into four areas.

Structure and shell

This is the physical building:

• foundations
• ground floor
• drainage
• external walls
• insulation
• roof
• structural steel
• windows
• external doors

For many extensions, this is the largest proportion of the budget.

Foundations alone can become a major cost where ground conditions are difficult, or where deeper foundations, piling or other engineering solutions are required.

Internal services and fit-out

Once the shell is complete, the new room still needs to function as part of the home.

This can include:

• electrics
• lighting
• heating
• plumbing
• plastering
• flooring
• internal doors
• decorating
• kitchen or bathroom installation

This is where specification becomes particularly important.

Laminate flooring, standard radiators and a mid-range kitchen produce a very different final bill from natural stone, underfloor heating, bespoke cabinetry and premium sanitaryware.

Professional fees and approvals

An extension is not simply a case of paying a builder to start digging.

Depending on the project, you may need:

• architectural drawings
• planning advice
• a planning application
• structural engineering
• building regulations drawings
• building control
• drainage design
• party wall advice
• specialist surveys
• construction insurance

Homebuilding & Renovating reports typical architectural fees of around 3–7% of build cost for design services, with full project-management services potentially reaching 8–15%. Structural engineers and other professional services are additional.

Most extensions require Building Regulations approval even when planning permission itself is not required.

The standard householder planning application fee in England is currently £548 for alterations to a single house. Some extension projects fall under permitted development. Larger permitted-development extensions may need prior approval instead, and Planning Portal lists that fee at £249.

Building control fees vary between local authorities. Woking Borough Council's charges from 1 April 2026 show a total of £825 for a 10–40m² single-storey extension under its full-plans route, with larger extensions charged at higher rates.

VAT can make a big difference

Many homeowners compare quotes without checking whether VAT is included.

Most ordinary extension projects to occupied homes are subject to 20% VAT. Some qualifying work can benefit from a reduced rate. The precise treatment depends on the project and the property, so confirm it with the contractor and HMRC's guidance on buildings and construction.

When comparing builder quotations, always check: is this price including VAT?

A quote of £80,000 excluding VAT is not an £80,000 project. At 20% VAT, it becomes £96,000.

Don't forget the contingency

Even a very good set of drawings cannot predict every condition hidden inside or beneath an existing house.

You can encounter:

• unknown drainage
• poor foundations
• unexpected structural problems
• buried services
• asbestos
• difficult ground conditions
• changes required after opening-up works
• additional steelwork
• damaged existing materials
• specification changes

A sensible homeowner should maintain a 10% contingency, and potentially more on a complex renovation. Homebuilding & Renovating also recommends allowing at least 10% for unexpected issues.

For example:

£100,000 planned project

• £10,000 contingency

= £110,000 accessible budget

The contingency should be money you have available but do not expect to spend.

Why your final finish matters so much

Two homeowners can build the same 25m² extension and end up with dramatically different final costs.

The difference might come from:

Windows and doors

uPVC windows are usually significantly cheaper than large aluminium bifold systems or bespoke architectural glazing.

Kitchen

A kitchen can range from a relatively modest off-the-shelf installation to a bespoke room when cabinetry, appliances, worktops and specialist finishes are considered.

Flooring

Laminate, engineered timber, porcelain, natural stone and other materials have very different supply and installation costs.

Heating

Standard radiators are one thing. Underfloor heating, heat pumps, zoning and upgraded controls introduce additional costs.

Lighting and electrics

The number of sockets, lighting circuits, exterior lighting, smart controls and AV points can all increase the electrical specification.

Roof design

A straightforward pitched or flat roof is generally simpler than a complicated roof with rooflights, lanterns, vaulted ceilings or structural glazing.

Doors

A standard patio door is very different financially from a large-format, slim-frame aluminium sliding system.

This is why price per square metre should be treated as an early budgeting tool, not the final answer.

Does the size of the extension determine the price?

Not entirely.

Smaller extensions can sometimes have a higher cost per square metre, because many costs are fixed.

You might still need:

• structural engineering
• building control
• scaffolding
• site setup
• skips
• structural steel
• demolition
• an electrical connection
• plumbing
• project management

Whether the extension is 15m² or 30m², many of those costs still exist. Doubling the size of an extension does not necessarily double the cost.

What is happening to construction costs in 2026?

Construction pricing is still moving, although the rate of increase has moderated compared with the extreme inflation seen earlier in the decade.

The BCIS All-in Tender Price Index increased by an estimated 3.2% over the year to Q3 2026, with tender prices rising by around 0.7% between Q2 and Q3 alone.

The Office for National Statistics also reported that construction output price growth was 1.9% in the year to June 2026.

For a homeowner, the practical lesson is straightforward: a quote that looks reasonable today may not remain valid indefinitely.

That matters when you are planning a project several months ahead, because labour availability, material prices and contractor workloads can all affect tender prices.

Planning permission in Surrey

Not every extension requires a full planning application.

Many house extensions can fall under permitted development, provided the relevant limits and conditions are met. That should never be assumed.

Planning Portal guidance is that restrictions can apply depending on the size and position of the proposed extension, previous extensions, conservation status and other planning constraints. Article 4 directions can also remove permitted development rights in certain areas.

Surrey also contains a wide range of conservation areas and properties subject to additional planning constraints.

Before commissioning expensive building work, establish:

1. What planning rights apply to the property?
2. Whether previous extensions affect the calculation.
3. Whether the property is listed or in a conservation area.
4. Whether an Article 4 direction applies.
5. Whether Building Regulations approval is required.
6. Whether party wall procedures apply.

Householder planning applications are generally subject to an eight-week decision period once validated. The overall project timeline is usually longer once drawings, design development and pre-application work are included.

What about the Community Infrastructure Levy?

For many homeowners, the Community Infrastructure Levy will not be an issue.

Government guidance states that residential extensions which enlarge the existing principal dwelling and do not create an additional dwelling are exempt, and residential extensions under 100m² are covered by the minor-development exemption, subject to the applicable rules.

It is still sensible to check the position with the relevant local planning authority, particularly for unusual projects or proposals that create an additional dwelling.

The biggest mistake homeowners make when budgeting

The biggest mistake is usually not choosing the wrong builder. It is starting the project without a sufficiently defined scope.

A homeowner might receive three quotations:

• Builder A: £72,000
• Builder B: £88,000
• Builder C: £104,000

At first glance, Builder A appears cheaper.

What happens if Builder A has not included:

• VAT
• kitchen installation
• flooring
• decoration
• structural steel
• building control
• landscaping
• waste removal
• drainage alterations
• final connections
• certain windows or doors?

The cheapest quotation is not necessarily the cheapest project. The only meaningful comparison is between like-for-like scopes of work.

A better way to manage your extension project

The financial risk does not disappear once you have chosen a builder.

During a typical extension, there are dozens of decisions and payment points. Work progresses. Materials change. Additional work is requested. Designs are amended. Unexpected issues are found. Payments need to be made at the right time.

A clear digital record is extremely valuable. Instead of a collection of paper quotations, emails, invoices and WhatsApp conversations, the project should record:

• what was agreed
• what is being built
• what has changed
• what has been completed
• what has been paid
• what remains outstanding
• what evidence supports completion

How Fort helps homeowners manage construction projects

Fort was built around exactly this problem.

Fort is a construction platform designed to bring homeowners and tradespeople together, and to provide the structure needed to manage the project after the builder has been found.

Homeowners can create a project, present the work to tradespeople, manage project information, communicate with contractors and keep a digital record of the project. Fort also allows homeowners to invite a contractor they already know, rather than requiring them to find their builder through the platform.

The platform uses milestone-based payments, so the project can be divided into defined stages rather than relying on large upfront payments. Payments are associated with agreed milestones, which helps keep money and project progress aligned. See how milestone payments protect homeowners.

Fort's homeowner tools include:

Project management

Keep plans, documents, communications and project progress together. Explore the homeowner features.

Fortified milestone payments

Payments are structured around project stages, so homeowners can see what they are paying for and when.

Verified tradespeople

Fort carries out verification checks on companies joining the platform. That gives homeowners an additional layer of information when choosing who to work with. It does not replace your own checks: see how to vet a builder before hiring.

Dispute resolution

If something goes wrong, Fort has a structured dispute process. Where appropriate, a third-party chartered surveyor can be organised to assess the work against the agreed project information.

The aim is simple: make the financial and administrative side of residential construction clearer for both homeowners and tradespeople.

What should you budget for your Surrey extension?

As a starting point, a homeowner considering an extension in Surrey in 2026 could use this broad guide:

£50,000–£80,000
A small, relatively straightforward extension with a standard specification.

£70,000–£110,000
A typical medium-sized single-storey extension with good-quality finishes.

£90,000–£150,000+
A larger extension, kitchen extension, or project involving more substantial structural work and premium finishes.

£120,000–£180,000+
A large wraparound, high-specification or two-storey project.

These figures can go significantly higher for exceptional architectural projects, difficult sites or premium interiors.

The size of the extension is only one part of the calculation.

How Fort can help with the project

Planning a house extension is a major investment, and choosing the right builder is only one part of the process. Fort is designed to help homeowners manage the construction project from the moment they start looking for a tradesperson through to completion, bringing project planning, communication, documentation and payments together in one place.

You can post your project and connect with tradespeople through Fort, or invite a contractor you already know. Tradespeople on the platform go through Fort's verification process.

Once your builder has been appointed, Fort helps you organise the project in one place. Keep project information, documents, messages, agreed work and updates together, creating a clear digital record of what has been discussed and agreed. That is particularly valuable on larger projects, where changes, decisions and costs can quickly become difficult to track.

Fortified milestone payments let homeowners and contractors agree specific stages of work, with payment linked to those milestones rather than large upfront payments.

Where the scope of work changes, Fort can also record variations and agreements, so both sides can see what changed, why it changed, and what it does to the project.

And while nobody starts a building project expecting a dispute, things do not always go according to plan. Fort provides a structured dispute-resolution process, with the option of involving an independent chartered surveyor where appropriate.

Whether you are planning a small rear extension, a new kitchen, a two-storey extension or a larger renovation, Fort brings the people, information, payments and project stages together.

Create an account to set the project up, or read the homeowner guide.

Your home. Your project. Your money. Managed with Fort.

Final thoughts

A house extension can be an excellent way to create additional space while remaining in a property you already know.

The financial side needs to be approached realistically. For Surrey homeowners, a sensible starting point is to budget towards the higher end of national extension-cost guidance, particularly for smaller projects, kitchen extensions, and projects with premium glazing or complex structural work. Current industry benchmarks, South East pricing and continued tender-price movement all support allowing a healthy margin rather than budgeting to the cheapest online estimate.

Think beyond "how much will my extension cost?":

• What exactly am I buying?
• How will the work be paid for?
• How will changes be recorded?
• How will I know when a stage is complete?
• What happens if something goes wrong?

The best-managed extension is the one where the scope, costs, programme, payments and responsibilities are clear from the beginning.

Sources and methodology

The figures in this article are indicative 2026 planning estimates, not fixed market prices or quotations. They combine published UK extension-cost benchmarks with a practical allowance for the higher-cost South East market and typical homeowner project overheads. Actual prices vary by property, location within Surrey, site conditions, contractor, design and specification.

The sources used for those benchmarks are listed below.

Last reviewed: September 2026.