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How Much Is a Side Extension? Side Return Extension Costs 2024


Architectural Design


House Extensions

How Much Is a Side Extension? Side Return Extension Costs 2024


When it comes to expanding your living space, one of the most popular methods among homeowners is to build a side extension or side return extension. These extensions provide you with that much-needed extra space and significantly increase the value of your property. However, undertaking such a project involves financial planning, and the foremost question that arises is – how much does a side extension cost?

This guide aims to give an in-depth understanding of the costs involved in building a side extension or side return extension as projected for the year 2024. It will equip you with knowledge about initial financial outlay and long-term expenses, which will help you plan meticulously and avoid unwelcome financial surprises. We understand that every project is unique, and its cost can vary depending on unique factors such as the size of the extension, the property’s location, the complexity of the design, and the construction materials used. We’ll address these elements throughout this guide to help you estimate a more accurate cost for your specific needs.

Factors Affecting Side Extension Costs

While it’s challenging to provide an exact figure for a side extension without understanding the particulars of your project, it’s essential to note several factors can significantly influence its overall cost, such as:

1. Size of the Extension

The size of your proposed side extension dramatically affects the overall costs. Larger extensions naturally require more materials, longer labour hours, and potentially more complex architectural designs and planning permissions.

2. Design Complexity

Simply put, the more complex the design, the higher the cost. If your design includes specific architectural elements like skylights, bi-fold doors, and bespoke kitchens, or involves dealing with structural issues such as supporting walls, expect these aspects to push your budget higher.

3. Building Materials

Building materials can significantly impact the cost of the extension. High-quality, durable materials tend to be more expensive, but they also last longer and add more value to your home in the long run. It’s about balancing the initial cost outlay with the long-term benefits of their use.

4. Location

The property’s geographical location can impact the cost of a side extension due to differences in local labour rates and the cost of materials within the given locale. Specific areas may also impose particular building regulations, which could add to the cost, for example, the requirement to obtain special planning permissions.

5. Professionals involved

Your side extension project will likely involve architects, builders, surveyors, and other specialists depending on the scale and complexity of the job. Their professional fees will form a significant part of your overall budget.

6. Planning Permission and Building Regulations

Depending on your extension’s size, design, and location, you may need to apply for specific types of planning permission or comply with certain building regulations or conservation laws, each of which will incur additional costs.

By understanding the key factors and how these will influence the above points, you can get a clearer picture of the potential cost of your side extension to help you devise a more realistic budget plan.

Average Cost of Side Extensions

Taking the diverse factors that can influence the cost of a side extension into account, the price range for them may vary significantly. However, a general estimation based on average rates and typical scenarios can be highlighted:

Basic Construction Cost

A basic side return extension with standard finishes and simple construction could cost somewhere between £1,400 to £2,300 per square meter. It usually includes the cost of a standard kitchen, the cost of underfloor heating, and the fees for the required planning permission and building regulations application.

Medium Quality Extensions

A medium-range side return extension typically involves more bespoke designs and higher-quality materials and could cost you from £2,300 to £3,400 per square meter. This might include a higher-specification kitchen or bathroom, high-quality flooring, additional architectural features, and possibly professional project management fees.

High-End Extensions

If you plan to opt for a luxury or high-end side extension, prices can go beyond £3,500 per square meter. These extensions include top-of-the-range materials, designer kitchens or bathrooms, bespoke architectural elements, landscaping, and potentially higher architect and professional fees.

Please note that these costs are ballpark figures for the year 2024 and can change depending on various factors discussed earlier.

Additional Costs to Consider

While the figures provided above give a good indication of the expected costs, they are not exhaustive. There are several additional costs that you might need to consider when planning your budget for a side extension or side return extension. These include:

  • Architectural Fees: Depending on the complexity of the project, these can range from 7% to 15% of the total construction cost.
  • If your project requires the expertise of a structural engineer, this may add anywhere between £400 to £2,000 to the overall value of the project.
  • Surveys required to be undertaken on the property can be anywhere in the range of £300 to £1,000 depending on the size of the property.
  • Building control fees may apply, and typically range between £200 – £600.
  • In the highly likely scenario that you’ll need planning permission, these fees can range anywhere between £200 to £250.
  • Additional renovations such as landscaping, interior design, utilities, insulation or bespoke fittings can increase your budget.
  • It’s crucial to have insurance in place to protect your investment from unforeseen circumstances, the cost of which depends on the value of the project.

Always remember that unforeseen issues can arise during construction which might inflate your budget further. Hence, it’s wise to have some extra contingency funds set aside.

Strategies to Reduce Costs

Investing in a side extension can be a costly venture, but there are ways to make it more cost-effective without compromising on quality. Here are some strategies that could help you save money on your side extension:

1. Architectural drawings & detailed plans

Having a clear vision of your project by way of an architectural drawing plan allows you to have a clear and thorough plan in place, before any building work commences, minimising the risk of any costly mistakes or changes during the construction phase. Laying out a detailed plan before the construction begins can help you forecast the possible costs and prevent unexpected expenses. Alongside the architectural designs, this should outline materials required, and a timeline for the construction process.

2. Opt for simple designs

The more intricate your design, the higher the cost. Opting for simple, functional designs over elaborate ones that require custom work and intricate detailing can free up the finances required to enhance other aspects of the build that may increase the property value, such as underfloor heating or bespoke kitchen designs. Remember, simplicity doesn’t mean settling for less. With the right planning, a minimalist design can be as beautiful and functional as a complex one.

3. Hire a contract administrator

It’s a common belief that independently managing an extension project yourself can save time and money, although should you run into a scenario of your project overshooting its completion deadline, it can result in substantial costs further down the road. You can read more about our contract administration services here.


There are numerous factors that contribute to the cost of a side extension or a side return extension, which with some effective planning, can allow you to redistribute finances to higher-value areas of the project, or keep the overall cost of the project low.  By taking some of the cost-saving strategies outlined in this guide into consideration, you can ensure that your project is delivered to your expectations in regard to its design, specification, or overall cost. 

A key detail to remember is that cutting corners on quality and process, whilst cost-efficient in the short-term, can often lead to longer-term issues with additional investment required to reach points of resolution. Investing in reliable construction materials and contract administrators to ensure quality of delivery is a worthwhile outlay that ensures your new space stands the test of time without unexpected costly repairs.

With over twenty years of experience and a diverse portfolio consisting of the architectural design, planning and construction of extensions, we’re well placed to help you with your side return extension project. Get in touch with one of our experts today to discuss your requirements, and see how we can help you.

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