Double Storey Extension Cost UK (2026): Complete Price Guide

Although building across two floors requires a larger investment than a single storey extension, it often delivers considerably more floor space for a lower cost per square metre than carrying out two separate projects.

For many homeowners, a double storey extension is a cost effective solution that creates extra bedrooms, expands the ground floor and adds valuable space without the expense of moving house. The final extension cost depends on the size of the project, property location, structural complexity, specification and whether planning permission is required.

Whether you're extending a semi detached home, modernising an existing house or planning a completely new extension, this guide explains the typical costs, what affects your budget and how to get the best value from your investment.

If you're planning a project north of the border, our guide to house extensions Scotland explains the complete design and construction process in more detail.

Double Storey Extension Cost at a Glance

In 2026, most double storey extensions cost between £75,000 and £195,000+, with construction costs typically ranging from £2,000 to £3,200 per square metre. While the overall extension cost is higher than a single storey extension, two storey extensions usually provide more floor space and better long-term value because many construction costs are shared across both floors.

Why a Double Storey Extension Often Offers Better Value

One of the biggest misconceptions is that a double storey extension costs twice as much as a single storey extension. In reality, that's rarely the case.

Every extension starts with the same essential work. Groundworks, foundations, drainage, scaffolding and site preparation are required whether you're building one floor or two. By adding a second floor at the same time, you're making better use of those fixed costs rather than paying for another building project years later.

This is why many architects and contractors recommend building upwards if your long-term plans include needing more bedroom space. The additional cost of constructing the first floor is often significantly lower than homeowners expect because much of the expensive groundwork has already been completed.

A single storey extension remains an excellent choice if your only objective is creating a larger kitchen, dining room or utility room. However, if you expect your family to grow or need more living space in the future, a double storey extension usually provides better long-term value.

Another major advantage is preserving garden space.

Instead of extending deep into the rear garden, building across two floors allows you to create additional floor area while maintaining more outdoor space. This is particularly valuable for semi detached homes where gardens may already be limited.

Many homeowners also compare extending with moving house.

While buying a larger property may seem attractive, the additional costs soon add up. Estate agent fees, legal fees, removals and renovation work can easily cost tens of thousands of pounds before you've even settled into your new home.

Extending your existing house allows you to remain in an area you already know while tailoring the property to suit your future needs.

Where Does Your Budget Go?

When looking at a quotation, it's important to understand that construction is only one part of the total extension cost.

A typical double storey extension budget is often divided into several areas.

Construction and labour account for the largest proportion of the budget. This includes foundations, brickwork, roofing, insulation, windows, structural work, external doors and internal construction.

Fixtures and finishes vary considerably depending on your specification. Standard kitchens, flooring and bathrooms keep costs under control, while premium materials and bespoke joinery increase the overall cost.

Professional fees are another important part of any budget.

These usually include:

• Architectural drawings

• Structural engineers

• Structural engineer fees

• Building Control inspections

• Planning consultants where required

Architect fees generally range between £800 and £2,500 depending on the complexity of the project.

Planning permission applications themselves usually cost around £200, although the supporting drawings and reports increase the total professional fees.

Most experienced builders also recommend allowing a contingency fund of around 10% to 15% of the project value. Unexpected drainage issues, hidden structural defects or changes during construction can all increase costs, particularly in older properties.

What Has the Biggest Impact on Extension Cost?

No two projects are identical, which is why the storey extension cost varies so much between properties.

Extension Size

The size of the new extension has the greatest influence on the final price.

Larger extensions require more labour, more materials and longer construction periods. However, they often reduce the cost per square metre because fixed expenses such as scaffolding, site setup and professional fees are spread across a larger floor area.

Property Location

Where your property is located also plays a major role.

Projects in the South East and London generally command higher prices than elsewhere in the UK due to labour demand and material costs.

The same extension can cost considerably less in other regions depending on contractor availability and local market conditions.

Structural Complexity

The structural design of your extension is another significant cost factor.

Projects involving major alterations to the existing building, complicated roof structure changes or long-span steel beams require additional design work from structural engineers.

Removing load-bearing walls, changing the roof pitch or creating large open-plan spaces all increase both labour and engineering costs.

Ground conditions also influence pricing. Poor soil, drainage diversions and difficult site access can increase groundwork costs before construction even begins.

Finally, specification has a major impact on the overall build cost. Premium glazing, luxury bathroom fitting, bespoke staircases and high-end kitchens can each add thousands of pounds to the final budget.

If your plans include extending your kitchen as part of the project, our guide to kitchen extension cost explains the main pricing factors and what to expect.

For a broader comparison across every extension type, you can also read our complete guide to house extension cost.

Planning Permission for a Double Storey Extension

One of the first questions homeowners ask is whether a double storey extension will require planning permission.

In most cases, the answer is yes.

Unlike many smaller projects, larger two storey extensions often exceed permitted development limits, meaning an application must be submitted to your local authority before building work can begin.

As a general rule, your extension cannot occupy more than half of the total area of land surrounding the original house. Design, height and proximity to neighbouring properties are also taken into account.

If your property sits within a conservation area or is a listed building, additional planning restrictions are likely to apply.

Although planning permission typically costs around £200, you'll also need architectural drawings and supporting documentation. Architect fees generally range between £800 and £2,500 depending on the complexity of the proposal.

Planning and preparation can take anywhere from a couple of weeks to several months, so it's worth factoring this into your project timeline.

Even where planning permission has been granted, your extension must still comply with current building regulations covering structural safety, fire protection, insulation, drainage and energy efficiency.

If your extension affects a neighbouring property, you may also need a party wall agreement before work begins. This is particularly common for semi detached homes and terraced properties where construction takes place close to a shared boundary.

An experienced extension company should guide you through planning permission, Building Control requirements and any approvals required before work starts.

How Much Does a Double Storey Extension Cost Per Square Metre?

Many builders calculate projects using a cost per square metre because it provides a useful way of comparing different extension types.

In 2026, a realistic build cost is:

These figures cover construction only and don't necessarily include professional fees, VAT or premium finishes.

Several factors influence the final cost per square metre, including:

• Property location

• Site access

• Structural complexity

• Roof structure

• Roof pitch

• Foundation design

• Material costs

• Internal specification

Simple rectangular extensions are generally the most affordable because they require less structural work and fewer complex roof details.

Projects with vaulted ceilings, large areas of glazing or bespoke architectural features naturally cost more to construct.

Rear Extension or Two Storey Side Extension?

The extension type you choose has a major impact on both cost and practicality.

A rear extension remains the most popular option because it creates generous open-plan living areas while connecting the house with the garden.

A two storey side extension is particularly common on semi detached properties. By extending into the side plot, homeowners can add valuable downstairs accommodation while creating additional bedrooms and bathrooms upstairs.

Some projects combine both approaches.

Wraparound extensions merge a rear extension with a side extension, creating substantial additional floor area on the ground floor while allowing the first floor to expand above.

Although wraparound extensions involve a higher overall extension cost, they can completely transform the layout of an existing house and make better use of awkward external space.

The right solution depends on your plot, budget and long-term plans.

How Much Does a Two Storey Side Extension Cost?

A two storey side extension is a popular choice for semi detached homes where there is unused space at the side of the property. Rather than extending into the rear garden, homeowners can increase both ground and first-floor accommodation while preserving more outdoor space.

In most cases, a two storey side extension costs between £90,000 and £170,000, although the final extension cost depends on the overall floor area, roof structure, structural work and internal specification. Projects that include a new kitchen downstairs and additional bedroom space with a bathroom upstairs generally sit towards the higher end of the price range.

As with any double storey extension, planning permission is usually required, and a party wall agreement may also be needed where work takes place close to a neighbouring property. Site access, property location and structural complexity can all affect the final build cost.

Typical Construction Timeline

One advantage of a double storey extension is that it doesn't take twice as long to build as a comparable single storey project.

Once planning approval has been secured, a typical programme looks something like this:

Groundworks are often the most unpredictable stage because contractors may encounter poor soil conditions, hidden drainage or existing foundations that require alteration.

Once the foundations are complete, the shell of the new extension usually progresses quickly.

The final stages include electrical work, plumbing, plastering, decorating, flooring and bathroom fitting, all of which vary depending on the specification chosen.

Larger or more complex projects may take longer, particularly where bespoke finishes or specialist materials are involved.

Hidden Costs Homeowners Often Miss

When budgeting for a double storey extension, it's easy to focus purely on the contractor's quotation.

However, several additional cost items are frequently overlooked.

These include:

• Scaffolding

• Building Control charges

• Structural engineer fees

• Planning application costs

• Architectural drawings

• Skip hire

• Utility diversions

• Landscaping after construction

• Decorating existing rooms

• Temporary living arrangements where necessary

Construction and materials generally account for around half of the total extension budget, but fixtures, fittings and finishes can quickly increase spending if premium products are selected.

High-end kitchens, luxury bathrooms and bespoke joinery are among the biggest contributors to rising costs.

Setting aside a contingency fund of around 10% to 15% of the total cost provides protection against unexpected structural work or unforeseen issues uncovered during construction.

Regional Cost Differences

Property location has one of the biggest influences on extension pricing.

Projects in London typically cost between 20% and 40% more than similar developments elsewhere in the UK due to higher labour costs and greater demand.

The South East also commands above-average prices, while many areas of Scotland and northern England offer more competitive construction rates.

That doesn't necessarily mean choosing the cheapest contractor represents the best value.

Experience, workmanship, communication and project management often have a much greater impact on the success of an extension than simply selecting the lowest quotation.

If you're planning a project in the west of Scotland, our guides to house extensions Glasgow and house extensions Ayrshire explain the design and construction services available across both regions.

Does a Double Storey Extension Increase Property Value?

A well-designed double storey extension doesn't just create more living space. It can also make your property more attractive to future buyers.

While the exact increase depends on the property location, quality of construction and local housing market, many extensions add between 10% and 20% to a home's value. Some projects that create extra bedrooms and an additional bathroom can increase property value by as much as 25%.

The best returns are usually achieved when the extension improves the way a home functions rather than simply making it larger.

For example, converting a cramped three-bedroom property into a spacious four-bedroom family home with a larger kitchen and open-plan living area is likely to appeal to a much wider range of buyers.

Research also suggests that quality extensions can return around £1.20 to £1.50 in value for every £1 invested, although this varies depending on the location and standard of finish.

If you're planning to remain in your home for many years, the additional comfort and flexibility often become just as valuable as the financial return.

Double Storey Extension vs Other Extension Types

Although a double storey extension is an excellent option for many homeowners, it isn't always the right solution.

Here's how it compares with other popular extension types.

A loft conversion can be a practical alternative if you only require additional bedroom space, while wraparound extensions are ideal for creating expansive open-plan layouts.

If your existing house has enough external space and you need both downstairs and upstairs accommodation, a double storey extension often represents the best balance between additional floor area and long-term value.

Choosing the Right Extension Company

Choosing the right contractor is just as important as setting the right budget.

Rather than selecting the cheapest quotation, compare companies based on their experience with similar projects, quality of workmanship and customer feedback.

Look for extension specialists that provide:

• Detailed written quotations

• Fixed pricing where possible

• Public liability insurance

• Employer's liability insurance

• Structural engineering support

• Project management throughout the build

• Clear communication

• References and completed projects

• Warranty options

It is also worth checking memberships with recognised organisations such as the Federation of Master Builders (FMB), National Federation of Builders (NFB) or Local Authority Building Control (LABC) where appropriate.

Obtaining at least three quotations allows you to compare not only price but also specification, build quality and what's included.

Several companies have built strong reputations for delivering home extension projects across the UK, including Designer Garden Rooms, Resi, Plus Rooms, Absolute Lofts, Touchstone Lofts, Simply Extend and Baufritz UK. Each offers different services, so it's important to compare experience with projects similar to your own.

A reputable company should also explain the planning process, Building Control requirements, expected construction timeline and any potential challenges before work begins.

Is a Double Storey Extension Right for You?

A double storey extension is a significant investment, but for many homeowners it offers a practical alternative to moving house.

By extending your existing property, you can create more living space, add extra bedrooms, improve the layout and potentially increase property value without leaving an area you already enjoy.

Although the overall extension cost is higher than a single storey extension, building upwards often delivers better value because many construction costs are shared across both floors.

Before starting any project, obtain detailed quotations, allow for professional fees and contingency, and work with experienced specialists who understand structural design, planning permission and building regulations.

Taking the time to plan properly can help you avoid unexpected costs and ensure your new extension adds lasting value to your home.

Frequently Asked Questions

How much does a double storey extension cost in 2026?

Most projects cost between £75,000 and £195,000+, although the final price depends on size, specification, property location and structural complexity.

What is the average cost per square metre?

Construction typically costs between £2,000 and £3,200 per square metre in 2026.

Is a double storey extension cheaper than building two single storey extensions?

In many cases, yes. Because foundations, scaffolding, roofing and site setup are shared across both floors, building one double storey extension is usually more cost effective than completing two separate projects.

Do I need planning permission?

Most larger two storey extensions require planning permission from the local authority. They must also comply with current building regulations.

How long does construction take?

Most double storey extensions take between 8 and 14 weeks to build once work begins, although planning and preparation can take considerably longer.

How much should I budget for professional fees?

Architects, structural engineers and other professional fees generally account for around 10% of the overall project budget.

How much contingency should I allow?

Most professionals recommend allowing an additional 10% to 15% of your total budget for unforeseen costs.

Will a double storey extension increase my property's value?

A high-quality extension can add between 10% and 20% to property value, with some projects achieving even greater returns where they create additional bedrooms and bathrooms.

Is a double storey extension better than moving house?

For many homeowners, extending is more affordable than moving once estate agent fees, legal fees, Stamp Duty and removal costs are considered. It also allows you to remain in a location you already know while creating a home that better suits your needs.