How Much a Side Return Extension Costs in London

A house with a side extension

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January 10, 2024

There is a lot to think about when you are planning a side return extension in London, especially the cost. Below, we have taken a look at the various factors that impact the price, including how much you can expect to spend on your project.

Average Costs of a Side Return Extension in London

You can expect to pay between £30,000 and £150,000 for a side extension in London. The range is large as there are a lot of variables to consider. For example, working with a party wall or adding garden space will increase the cost, as can extending above the ground floor and creating a two storey property.

More often than not, tradespeople will quote for an extension on a per square metre basis.

Costs by Type of Extension

The side return extension cost can vary hugely, depending on the type of extension and its size. On average, you should expect to pay between £30,000 and £65,000 for a side return extension on terraced houses, though this cost is likely to be on the higher end in London.

One Storey Side Return Extension

Type of Side Return Extension Low Cost High Cost Average Cost
Small extension, one storey £30,000 £45,000 £37,500
Per m2, one storey £1,500 £4,500 £3,000
Per m2, one storey, glass extension £1,500 £4,500 £3,000
3m x 5m extension, one storey £35,000 £50,000 £42,500

Two Storey Side Return Extension

Type of Side Return Extension Low Cost High Cost Average Cost
Small extension, two storey £45,000 £65,000 £55,000
Per m2, two storey £1,500 £4,500 £3,000
Per m2, two storey, glass extension £1,500 £4,500 £3,000
2m x 7m extension, two storey £100,000 £200,000 £150,000

Side Return Kitchen Extension

A side return kitchen extension is often specifically focused on creating more kitchen space or a brand new kitchen. The cost of a side return kitchen extension can vary between £5,000 – £14,000 but larger, more complex projects and those in London can cost up to £80,000.

A newly renovated kitchen

Glass Side Return Extension

Glass side return extensions tend to be more expensive than brick extensions, and this is reflected in the price. The average cost of a glass side return extension is £3,000 per m2.

Factors That Affect Costs

There are several factors that can impact the costs of building a side return extension, and these should be considered when you are determining your budget and resource allocation.

Size and Complexity

The size and complexity of the side return extension are the key factors that determine the cost. Larger or more intricate extensions tend to require more materials, labour and time, which will increase the cost.


The majority of extensions require utilities to make the space usable. Extending plumbing and electrical wiring to the side return extension space can add to the cost, especially if doing so is complex.

Choice of Materials

The choice of materials will impact the cost, as high end materials cost a lot more, as do any materials needed for custom features. Choosing simpler designs and standard materials is one way to reduce the cost of your project.

Property Accessibility

Accessibility is a big factor in determining the cost, as construction vehicles and equipment need to be able to access the building site. Homes with challenging access will require more time and effort, leading to higher costs.

Structural Changes

If structural changes are needed, such as removing load-bearing walls, the project will be more expensive. Structural changes often require engineering expertise, permits and compliance with building regulations, all of which quickly add up.

Costs Breakdown

A couple calculating costs in the kitchen


The cost for a side return extension includes labour costs, covering the tradespeople involved in construction, such as builders, carpenters, electricians and plumbers.


Materials 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


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


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.


The cost of an extension also includes fittings, fixtures and furnishings for the new space. 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 the plans or unexpected expenses that may arise.

Reasons to Build a Side Return Extension

A photo of a house refurbishment from the outside

There are a lot of reasons to build a side return extension, such as:

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.


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 that work with other aspects of your home.

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

It doesn’t matter whether you need a larger kitchen or a larger dining area, a side return extension gives you a lot of flexibility in regards to how you use the additional space. This ensures that the extension aligns with your specific lifestyle and needs.

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

Some side return extensions require planning permission, and this is usually due to the impact that the extension will have on the appearance and structure of your home. 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.

DIY Vs Hiring a Professional

When you are planning a side return extension, you need to decide between embarking on a DIY project or hiring a professional builder. There are pros and cons of each, which we have explained below.

DIY Side Return Extension

  • Cost Savings – One of the main benefits of the DIY route is the potential for saving money. By taking matters into your own hands, you can cut down on labour costs and have greater control over your budget.
  • Flexibility and Control – DIY projects allow you to work on your own schedule and have complete control over the creative and decision making processes. You can tailor the project to your specific preferences without relying on anyone else’s input. Of course, this often means that the project needs to be scheduled around other commitments, meaning that a DIY side return extension often takes longer.
  • Learning Opportunities – DIY provides an opportunity to acquire new skills and knowledge, as it’s a hands-on way to familiarise yourself with new tasks and skills. However, building a side return extension does require expertise and experience, and it’s likely to be above the skill set of someone who wants to learn as they go.

Hiring a Professional Builder

  • Expertise and Efficiency – Professional builders bring a wealth of experience and expertise to the project. Hiring a skilled individual ensures that the job is done efficiently and correctly, saving time and avoidable mistakes.
  • Quality Assurance – Professional builders adhere to industry standards, ensuring a level of quality that may be challenging to achieve with DIY. Their experience allows them to anticipate challenges and deliver a flawless final result, even for the most complex projects.
  • Time Savings – A DIY project can take a lot of time, but tradespeople are able to complete tasks quickly. This is vital if you have a time sensitive project or if you have a busy schedule.
  • Access to Resources – Builders have access to specialised tools, materials and resources that you are unlikely to have access to. This ensures that everything about the project is streamlined and completed to a high standard.

Finding a Builder

A builder holding a hard hat

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, 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:

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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.

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