How Much a Side Return Extension Costs in London

Many London properties, particularly those that are terraced or semi-detached, have that awkward strip of land stretching down their sides. Extending into this unused area is one of the most popular ways to transform your home, increasing square footage and light without sacrificing precious garden space.

London homeowners can expect to pay a premium for a side return extension, and there are countless factors that can impact the total price – from how high-spec your fittings are to the cost of your builder. Here we break down the costs, hidden costs and important things to think about when planning a side return.

Average costs of a side return extension in London

With so many shapes, sizes, design choices, and property nuances to consider, it can be tricky to understand exactly how much your side return will cost – there really are no identical projects. When you see average prices online, it’s important to understand whether these account for the shell of the building (with no fittings, fixtures, finishes or electrics) or include professional and admin fees (like architect or structural engineer’s fees and drawings, party wall surveyors and notices, and building regulations), and VAT. Depending on your plans and finishes, these additions can significantly increase the overall cost of your extension.

A simple way to think about your budget is to consider these key areas:

• Labour and building materials (which is what builders will quote you for)

• Client supply (items that aren’t included in your builder’s quote that need to be purchased – think kitchen cabinets, decorative lighting, tiles, etc)

• VAT (an additional 20% of your project cost)

• Admin and professional fees (up to about 20% of your project cost, depending on how you manage your project and what your plans are)

For ballpark total costs for a side return extension in London, you’re looking anywhere between £70,000-£250,000. The lower end of the scale will be a small extension with a basic design and low-cost finishes; the upper end will be large, potentially two-storey, with high-spec fittings and features.

In part this variation is due to the sliding scale of labour costs (opting for a small up-and-coming building company for to build your extension will be cheaper than using a bigger, more established one), but the biggest factor is the huge scope of fit-out options. Choosing a premium kitchen can easily add £30,000 to your expenses, while including other luxury elements like underfloor heating, bespoke glass or steel crittall doors can also hike the price up. Recent side return extension projects that we’ve worked on have cost on average £140,000–£170,000 for labour and building materials and £50,000 for client supply items, plus VAT.

More often than not, builders will quote for the shell of an extension on a per square metre basis. Working out how much additional space you want to add and calculating an estimate by looking at average London prices per square metre is the most accurate way to figure out what the base price for your extension might be.

Costs by type of extension

The side return extension cost can vary hugely, depending on the type of extension and its size. While adding a double-storey side return extension will be more expensive than building a single storey due to increased square footage, some costs will remain unchanged, like the foundations and roof.

It’s worth noting that for a side return to be practical and significantly enhance your home it should be adding at least 15 square metres, but this is on the small side – many London homeowners build extensions that are bigger than this, which should be taken into account when looking at average costs. The below costs are for labour and building materials.

Single storey side return extension

Type of Side Return Extension	Low Cost	High Cost	Average Cost
Per m2, one storey	£1,600	£4,850	£3,225
3m x 5m extension, one storey	£37,500	£53,500	£45,500

Double storey side return extension

Type of Side Return Extension	Low Cost	High Cost	Average Cost
Per m2, two storey	£1,600	£4,850	£3,225
2m x 7m extension, two storey	£107,000	£214,000	£160,000

Side return kitchen extension

A side-return kitchen extension is specifically focused on creating more kitchen space or adding a brand new kitchen (often both). Like all extension projects, the cost of a side-return kitchen extension can vary hugely, but average costs in London (for labour, building materials and fit) look like this:

Basic finish: £75,000-£95,000
Mid-range finish: £90,000-£120,000
High-end finish: £120,000-£160,000+

Glass side return extension

Glass side return extensions tend to be more expensive than typical brick extensions due to the added complexity of the build and specialised construction techniques required, plus they use more premium and often bespoke materials. Double or triple-glazed glass, integrated blinds, and frame options (standard aluminium frames vs. frameless structural glass for example) are key costs to consider when thinking about building a glass side return extension.

Similarly to standard side return extensions there is a huge variety in cost for a glass extension, but on average the total project cost in London looks like:

Mid-range finish: £115,000-£145,000

High-end finish: £145,000-£200,000+

Factors that affect costs

There are numerous factors that can impact the costs of building a side return extension. Understanding exactly what’s needed for your unique project is the only way to get a true sense of the final price.

Size and complexity

The size and design complexity of the side return extension are two key factors that determine the cost. Larger or more intricate extensions will require more time to build, therefore the labour cost will be higher, and the bigger the side return, the more building materials will be.

Utilities

Extensions require utilities like the rest of your home. Extending plumbing and electrical wiring to the side return extension space will incur a cost, particularly if it involves complex work – like moving pipes or the property’s waste disposal.

Choice of finish

One of the biggest cost factors is your choice of finish: premium materials and fixtures will increase your total spend significantly, as will custom elements like bespoke joinery. The most important features and budget non-negotiables are very personal and lifestyle dependent – some people might be set on a top-of-the-range kitchen and others on fancy floor tiles. It’s important to prioritise and do your research into where you can save and where you want to spend.

These are the sorts of fittings to consider for varying budgets:

Basic finishes: £1,500-£2,000/m²

• Basic ceramic floor tiles (£20-£40/m²)
• Standard laminate worktops (£40-£100/linear metre)
• Standard kitchen units (£3,000-£7,000 total)
• Standard white emulsion paint (£25-£40 per 5L)
• Basic pendant lighting (£50-£150 per fitting)
• uPVC windows (£500-£1,000 per window)
• Standard composite doors (£1,000-£2,000 installed)

Mid-range finishes: £2,000-£3,000/m²

• Engineered wood flooring (£60-£120/m²)
• Quartz or solid surface worktops (£250-£500/linear metre)
• Semi-bespoke kitchen units (£7,000-£15,000 total)
• Feature walls and higher quality paint (£40-£70 per 5L)
• Recessed spotlights with feature pendants (£1,000-£2,500 total)
• Aluminium-framed windows (£1,000-£2,000 per window)
• Bifold doors with standard glass (£3,000-£6,000 installed)

Luxury finishes: £3,000-£4,500+/m²

• Natural stone flooring (£80-£200+/m²)
• Marble, granite or high-end quartz worktops (£500-£1,200/linear metre)
• Fully bespoke kitchen units (£15,000-£40,000+ total)
• Specialist decorative finishes (£2,000-£5,000 for the space)
• Smart lighting systems (£3,000-£7,000+ total)
• Minimal frame or frameless glazing (£2,000-£4,000+ per window)
• Flush threshold sliding doors with triple glazing (£7,000-£15,000+ installed)

Property accessibility

Accessibility is a sometimes overlooked factor that can play into your total cost. In London, you need to consider the price of skips and skip permits (£70-£120 per week), parking costs, whether or not you need to store materials elsewhere, and the cost of a crane if need be (£800-£1,500 per day).

Structural changes

With an extension, some structural changes are always needed, and these require engineering expertise, permits and compliance with building regulations, all of which also incur a cost. Here are some typical jobs and cost brackets for structural changes for extensions:

Minor structural work: £3,000-£7,000

• Standard steel beam installation to open up side wall
• Minimal foundation work
• Standard roof tie-in to existing structure
• Basic structural calculations

Moderate structural work: £7,000-£15,000

• Multiple steel beams and columns
• Enhanced foundations (piling or deeper foundations)
• Underpinning small sections (£1,200-£2,000 per metre on average)
• Party wall adjustments
• Tree root protection measures

Major structural work: £15,000-£35,000+

• Substantial underpinning (£1,500-£2,500 per linear metre on average)
• Complex steel framework for glass structures
• Cantilever designs requiring enhanced structural support
• Party wall rebuilding
• Fixing structural defects to the existing building

Costs breakdown

Labour

The price provided in a contractor’s quote for a side return extension is largely labour costs, covering the tradespeople involved in construction, such as builders, carpenters, electricians and plumbers.

Materials

Materials also make up a large portion of the cost breakdown, including everything from the foundation and structural components to finishing materials, such as flooring, tiles, wallpaper and paint

Glazing

Investing in quality glazing will make up a key part of your budget. For example, energy efficient glazing is usually more expensive, but will lead to long term energy savings.

Architect

Architectural fees are an important part of the cost breakdown, especially if you choose an experienced professional. But, an architect is an important part of the planning stages of a side return extension.

Fittings

Fittings, fixtures and furnishings for the new space aren’t usually included in your contractor’s quote so should be factored in as extra costs. This includes items such as cabinets, lighting fixtures, furniture and other interior elements.

Additional costs

It’s always a good idea to have a contingency fund and part of your budget allocated to unforeseen circumstances, changes to plans or unexpected expenses that may arise. If you can, add an extra 20% to your total project cost to make sure you’re covered if any surprises do occur.

Reasons to build a side return extension

More living space

A side return extension helps to make the most of the available space in your home, extending your living area. This can be hugely beneficial in urban areas where outdoor space is limited, and a full extension is not an option.

Personalisation

When you have a side return extension build, you can tailor the design to suit your design preferences and lifestyle. You can choose a layout that works for your home, as well as finishes and interior design choices unique to you.

Increased property value

A side return extension can add value to your property. Adding square footage to your home can significantly increase its market value, an investment that will pay off when the time comes to sell.

Modern and functional

Side return extensions enable you to update your home’s layout and improve its functionality. You can reconfigure existing spaces to align with your contemporary living styles, such as by adding an open plan kitchen or dining area.

Flexible use of living space

While lots of people build a side return extension to increase their kitchen and dining spaces, you can do whatever you like with the additional square footage, depending on your needs and lifestyle. Often, the extra space allows for greater flexibility and takes on different roles throughout the day, offering room to work, socialise or relax.

More natural light

By extending the side of your home, you can bring more natural light into your home. Large windows, skylight and bi-fold doors can be incorporated into the extension, creating a brighter and lighter living space.

Planning permission

Do you need planning permission for your side return extension? The answer depends on where you live, your type of property and the scale of your plans. Planning permission is usually needed when the extension exceeds a certain size, or if it’s going to change the visual character of the building.

Factors such as the height, size and design of the extension, as well as its proximity to other properties, can mean planning permission is needed. It’s important to check with your local authority to determine whether planning permission is required for your specific build.

Finding a builder

There is no denying the importance of finding a professional, reliable and capable builder, and many people assume this task to be a lot more complicated than it actually is. With the right tools and a good understanding of what you are looking for, finding a builder can be quick and easy.

The Page

The Page is a great way of finding a builder for your extension, the process is designed to be straightforward and bespoke to your unique building needs.

Just send an inquiry, detailing what you need a builder to do. The Page then ‘matchmakes’ you to carefully selected tradesmen, all of which are chosen based on their specific expertise and suitability for the job. Hit the button below to send us your details:

Each tradesman on The Page is personally met, vetted and has had their previous work thoroughly assessed. This ensures that you are connected with a professional whose skills, reliability and quality of work align with the requirements of your project.

This personalised approach guarantees a level of confidence and assurance in the selection process, ensuring that you and your chosen tradesman have a good experience of pairing up.

Online Search

It’s always a good idea to search online when you are looking for a builder, using search engines and directories, such as Google and The Page, to find your ideal professional. Technology has transformed the way we search for service providers and tradespeople online, and online searches have become a key way of locating professionals skilled in bathroom renovation.

Using search engines allows you to discover local bathroom renovation specialists easily, and platforms such as The Page offer lists of reviewed and recommended tradespeople in your local area, providing you with a diverse selection to consider.

By comparing the experiences of previous clients through reviews and testimonials, you can gain valuable insights into a professional’s reliability and the quality of their work.

Ask Around

A lot of people underestimate the impact of asking around. When it comes to finding a builder, word of mouth is invaluable, as it gives you an insight into which builders are recommended and reliable in your local area.

It’s a more traditional approach to finding a builder, and all you need to do is ask friends, family, neighbours and colleagues. Chances are, someone you know has experienced the reliability and professionalism of an expert builder.