Single Storey Extension Cost Guide 2026

Whether you're extending a kitchen, creating a larger dining area or opening up your ground floor, understanding the likely costs can help you budget more accurately before work begins.

In 2026, the average single storey extension cost in the UK ranges from around £30,000 for a smaller project to £140,000+ for larger, high-specification builds. Most extension costs are calculated using the price per square metre, although labour costs, materials, design complexity and structural work all influence the final price.

If you're considering a larger renovation, our house extension Scotland service covers bespoke extension projects across Scotland.

How Much Does a Single Storey Extension Cost?

Most single storey extensions cost between £1,800 and £3,000 per square metre.

This means the overall house extension cost varies depending on the size of the extension project, the quality of materials selected and the amount of structural work required to integrate the new extension with the existing property.

For example:

• A 20m² single storey extension typically costs £40,000–£56,000.

• A 30m² extension generally costs £60,000–£84,000.

• A 50m² extension can reach £100,000–£140,000, depending on specification and finishes.

Larger home extensions often benefit from better cost efficiency because fixed expenses such as site setup and welfare facilities are spread across a larger floor area.

If you're comparing different types of projects, our house extension cost guide explains how prices vary across all extension types.

Single Storey Extension Cost Per Square Metre

Most builders estimate build cost using the total square metre area rather than offering one fixed price.

Typical costs per square metre are:

These figures usually include:

• Foundations

• Brickwork

• Roofing

• Insulation

• Windows and external doors

• Standard internal plastering

However, the materials cost can increase significantly if your new extension includes premium features such as:

• Structural glazing

• Roof lanterns

• Underfloor heating

• Aluminium sliding doors

• Bespoke kitchens

• Luxury flooring

• Smart lighting and heating controls

Higher-quality finishes naturally cost more, but they often improve durability, energy efficiency and the long-term value of your home.

Single Storey Extension Costs by Extension Type

Every extension project is different. The location of the extension, the existing structures and the amount of structural work required all affect the overall cost.

Rear Extensions

Rear extensions remain one of the most cost-effective ways to add extra space.

They typically cost from around £1,800 per square metre, making them ideal for homeowners wanting larger kitchens, dining areas or open-plan family spaces. They also provide one of the biggest increases in usable living space.

Rear extensions are commonly used for:

• Kitchen extensions

• Kitchen diners

• Family rooms

• Garden-facing living spaces

• Open-plan layouts

If your project is centred around your kitchen, our kitchen extension cost guide explains the typical costs, layouts and factors that influence your budget.

Side Extensions

A single storey side extension generally costs between £1,800 and £3,000 per square metre.

Although similar in price to rear extensions, side extensions can require additional structural work where external walls are removed and new openings are created between the extension and the existing property.

They're commonly used to create:

• Utility rooms

• Home offices

• Ground floor bathrooms

• Larger kitchens

• Additional storage

Return Extension

A return extension extends into the unused side return of a property and is especially popular on Victorian and traditional terraced homes.

Although a return extension usually costs more than a straightforward rear extension, it can completely transform narrow existing rooms into bright, open-plan living areas with improved natural light.

Projects of this type frequently require:

• Structural calculations

• Steel beams

• More complex roof construction

• Alterations to existing walls

These additional structural requirements increase labour costs and the overall build cost.

Wraparound Extension

A wraparound extension combines both a rear extension and a side extension into one larger project.

While this is one of the more expensive extension options, it allows homeowners to maximise space far more effectively than many smaller home extensions.

Wraparound extensions are commonly chosen to create:

• Large kitchen diners

• Open-plan family rooms

• Better garden access

• More natural light

• Flexible living space

If you're considering adding accommodation upstairs as well, it's worth comparing the costs with our double storey extension cost guide before deciding which option offers the best value.

What Affects Single Storey Extension Costs?

Even two extensions of the same size can have very different overall costs.

The biggest factors include:

Labour Costs

Labour costs account for a significant proportion of most home extension costs.

Projects in London and the South East typically cost 30% to 50% more than similar builds elsewhere due to higher demand and increased wages.

Material Costs

The materials cost depends entirely on your specification.

Premium brickwork, aluminium glazing, roof lanterns and luxury finishes can substantially increase your overall budget.

Choosing higher-quality materials often improves longevity and energy efficiency but increases upfront costs.

Structural Work

Structural work is one of the biggest variables affecting extension costs.

Steel beams, alterations to external walls, removing internal walls and reinforcing existing structures all require specialist design and installation.

More complex projects may add £2,000–£4,000 in additional steelwork and engineering costs before construction progresses.

Ground Conditions

Ground conditions are often impossible to assess fully until excavation begins.

Unexpected issues such as poor soil, tree roots, drainage diversions or deeper foundations can all increase costs considerably.

Excavation and foundation work are among the most common reasons projects exceed the original budget.

Design Complexity

Simple rectangular extensions remain the most cost-effective option.

However, the overall cost increases where projects include:

• Structural glazing

• Complex roof designs

• Bespoke layouts

• Large rooflights

• Corner glazing

• Premium architectural detailing

Although these features improve appearance and natural light, they also increase labour requirements, build time and material costs.

Professional Fees and Hidden Costs

Construction costs are only part of your overall budget.

Before starting your extension project, you should also allow for professional fees and additional costs, including:

• Architect fees

• Structural engineer fees

• Structural calculations

• Planning application fees

• Building Control fees

• Site surveys

• Drainage surveys

• Party Wall surveyor fees where required

• VAT on qualifying work

Finally, it's sensible to set aside a contingency fund of 10–15% of your overall budget to cover unexpected issues that may arise once construction begins. This helps avoid delays and gives you greater flexibility if hidden problems are discovered during the build.

Planning Permission for a Single Storey Extension

Planning permission is one of the first questions homeowners ask before starting a new extension. Fortunately, many single storey extensions can be built without submitting a full planning application.

Most projects fall within Permitted Development rights, provided they meet specific size and design limits.

For example, rear extensions extending up to 3 metres beyond the original rear wall of a terraced or semi-detached house can often be built without planning permission, provided the work complies with Permitted Development rules.

However, planning permission may still be required if:

• Your property is located within a conservation area.

• The extension exceeds Permitted Development limits.

• The property is listed.

• Previous extensions have already used your Permitted Development allowance.

• The design significantly alters the appearance of the property.

If planning permission is required, a standard householder planning application costs £206 in 2026.

Many homeowners also choose to apply for a Lawful Development Certificate. Although not compulsory, this document confirms that the extension complies with planning legislation and can prove useful when selling your property in the future.

If you're unsure whether your project requires consent, our guide to planning permission for extensions explains the rules in more detail.

Building Regulations

Even if your extension falls under Permitted Development, Building Regulations approval is still required.

Building Regulations ensure your extension is structurally safe, energy efficient and compliant with current construction standards.

During the build, inspectors will typically assess:

• Foundations

• Structural integrity

• Insulation

• Roof construction

• Electrical installations

• Drainage

• Ventilation

• Fire safety

Once the work has been completed and approved, you'll receive a Completion Certificate, which confirms the extension complies with Building Regulations.

This certificate is an important document to keep, particularly if you plan to sell your home in the future.

Does a Single Storey Extension Add Value?

For many homeowners, a single storey extension is about more than creating additional space. It can also increase the value of the property.

Although every home and location is different, research suggests a well-designed single storey extension can increase a property's value by around 5%.

Adding approximately 15m² of extra floor space can increase property value by around £21,000, while the average value created is estimated at approximately £2,300 per square metre.

In higher-value locations, that figure can be considerably greater.

Ultimately, the value added depends on factors including:

• Property location

• Local demand

• Quality of workmanship

• Design

• Layout improvements

• Size of the extension

Extensions that create practical living areas, larger kitchens and better connections to outdoor space often deliver the strongest return on investment.

How to Save Money on a Single Storey Extension

A well-planned extension doesn't always mean spending more. Making informed decisions early in the project can help control costs without compromising quality.

Some practical ways to save money include:

• Keeping the extension shape simple.

• Choosing standard-sized windows and doors.

• Avoiding unnecessary structural alterations.

• Finalising the design before construction starts.

• Comparing quotations from experienced builders.

• Setting aside a 10–15% contingency fund instead of relying on additional borrowing.

Although premium finishes can always be added later, changes to the structure after work begins are usually far more expensive.

Single Storey Extension or Another Home Improvement?

A single storey extension isn't the right solution for every property.

Depending on your home and budget, you may also consider:

• A loft conversion

• A wraparound extension

• A double storey extension

• A garden room

A loft conversion can create additional bedrooms without reducing garden space, while a double storey extension often offers better value per square metre if you also need upstairs accommodation.

Alternatively, a garden room can provide extra usable space with less disruption than a traditional extension.

If you're weighing up the options, our house extensions Glasgow or house extensions in Ayrshire service can help you choose the most suitable solution for your property.

Conclusion

A single storey extension remains one of the most effective ways to add extra living space and improve the functionality of your home.

While most projects cost between £1,800 and £3,000 per square metre, the final price will vary depending on the size of the extension, design complexity, structural work, labour costs and the quality of finishes you choose.

Taking time to understand planning requirements, professional fees and potential hidden costs before construction begins will help you build a more accurate budget and reduce the risk of unexpected expenses later in the project.

Whether you're planning a rear extension, side extension or wraparound extension, investing in careful design and experienced professionals can help you create valuable new space that enhances both your home and its long-term value.

Frequently Asked Questions

How much does a single storey extension cost?

Most single storey extensions cost between £1,800 and £3,000 per square metre. A typical project ranges from around £30,000 for a smaller extension to more than £140,000 for large, high-specification builds.

How much does a 20m² single storey extension cost?

A 20m² single storey extension typically costs between £40,000 and £56,000, depending on materials, labour costs, design complexity and ground conditions.

How much does a 30m² single storey extension cost?

Most 30m² extensions cost between £60,000 and £84,000, although premium finishes and complex structural work can increase the overall budget.

Do I need planning permission for a single storey extension?

Many single storey extensions fall under Permitted Development rights and do not require planning permission. However, projects that exceed development limits or are located in conservation areas may require approval from the local authority.

Do I need Building Regulations approval?

Yes. Building Regulations approval is normally required for house extensions, even when planning permission is not.

What is a Lawful Development Certificate?

A Lawful Development Certificate confirms that your extension complies with planning legislation. Although not always required, it provides useful evidence if you sell your property in the future.

Does a single storey extension add value?

A well-designed extension can increase the value of a property by around 5%, although the exact increase depends on location, design and the quality of the work completed.

Are rear extensions cheaper than side extensions?

In many cases, yes. Rear extensions are often more cost-effective because they usually require less structural work than side extensions.

What hidden costs should I budget for?

In addition to construction costs, you should allow for architect fees, structural engineer costs, structural calculations, Building Control fees, planning application fees where required and a contingency fund of around 10–15% for unexpected issues.