How Much Does an Extension Cost? 2023

Welcome to our definitive guide on “Home Extension Costs in the UK,” where we demystify the process, providing you with detailed insights and practical tips.

Whether it’s adding a new bedroom, expanding your kitchen, or creating a bespoke home office, understanding the financial implications is crucial.

In this guide, we delve deep into the average costs of single-story extensions, double-story expansions, and custom-designed renovations, ensuring you have all the information you need for a cost-effective and successful home improvement project.

The Cost of an extension

How much an extension costs.

The average cost of an extension are as follows

Size (Square Meters)Type of ExtensionQuality of MaterialsEstimated Cost (UK)Estimated Cost per Square Meter (UK)
10-20Single-StoryBasic£20,000 – £40,000£1,200 – £4,000
10-20Single-StoryMid-Range£40,000 – £70,000£2,000 – £4,250
10-20Single-StoryHigh-End£70,000 – £100,000+£3,000 – £5,250+
20-30Single-StoryBasic£40,000 – £80,000£1,200 – £2,150
20-30Single-StoryMid-Range£80,000 – £140,000£2,000 – £3,750
30-40Single-StoryHigh-End£140,000 – £200,000+£3,500 – £5,000+
40-60Two-StoryBasic£80,000 – £160,000£1,275 – £2,150
40-60Two-StoryMid-Range£160,000 – £280,000£2,000 – £3,750
40-60Two-StoryHigh-End£280,000 – £400,000+£3,500 – £5,000+
60+Custom DesignBasic£150,000 – £300,000£1,275 – £2,150
60+Custom DesignMid-Range£300,000 – £500,000£2,000 – £3,750
60+Custom DesignHigh-End£500,000 – £1,000,000+£3,000 – £5,000+

Please keep in mind that these are approximate cost estimates and can vary depending on various factors such as the location within the UK, specific project requirements, labor costs, and market conditions.

Factors Influencing Extension Costs

Before we delve into the specifics, let’s take a look at the key factors that play a significant role in determining the cost of a home extension:

1. Single vs. Double-Story Extension

The first decision you need to make is whether you want a single-story or a double-story extension. Double-story extensions typically cost more due to the complexity involved.

2. Project Scope and Size

The first and most significant factor influencing the cost of an extension is the scope and size of the project. It’s essential to determine what you want to achieve with your extension. Do you need an extra room, a larger living area, or a brand-new space altogether? The complexity and scale of your project will significantly impact the overall cost.

3. Material Choices

The quality of materials you choose for your extension will have a direct impact on the cost. Higher-end materials, such as hardwood floors or custom-made fixtures, will naturally come at a higher price point than more budget-friendly alternatives. Finding the right balance between quality and cost is crucial to ensure your extension meets your expectations while staying within budget.

4. Interior Finishes

The choice of interior finishes, such as flooring, paint, and fixtures, can significantly impact the overall cost. High-end finishes will increase your budget, while more budget-friendly options can help you save money without compromising on style and functionality.

5. Location and Permits

Your location plays a vital role in extension costs. Certain areas may have specific building regulations and permit requirements, which can add to the overall expenses. It’s essential to factor in permit fees and any necessary inspections.

6. Plumbing and Electrical

Integrating plumbing, electrical systems, and HVAC into your extension will impact the budget. These installations demand skilled professionals and careful planning.

7. Design and Architectural Fees

Investing in a well-thought-out architectural design can both enhance the aesthetics of your extension and optimize your budget. Hiring an experienced architect can help you create a design that maximizes space and functionality while minimizing unnecessary costs. The intricacy of the design, the choice of materials, and the need for structural alterations will all contribute to the final price.

8. Planning Permissions

Depending on your location and the nature of your extension, you may require planning permissions or permits from local authorities. These permissions can involve additional fees, so it’s essential to factor them into your budget. Consulting with a local planning authority or hiring a professional to handle the paperwork can streamline this process.

9. Compliance with Building Codes

Ensuring your extension complies with local building codes is essential, and this may require additional expenses.

10. Labor Costs

Labor costs are a significant portion of any extension project. The rates of architects, builders, electricians, plumbers, and other professionals involved can vary widely. It’s advisable to obtain multiple quotes and compare the qualifications and experience of the contractors to ensure you’re getting the best value for your money.

11. Project Timeline

The duration of your extension project can also affect its cost. Longer projects may incur additional expenses, such as temporary accommodations or storage solutions. Discussing a realistic timeline with your contractor can help you plan and budget accordingly.

Hidden Costs

Contingency Fund

Unforeseen issues can arise during any construction project. It’s advisable to allocate a contingency budget to account for unexpected expenses. Having a financial buffer can provide peace of mind and ensure that you can address any surprises without derailing your project.

Structural Changes

In some cases, extensions may require structural modifications to your existing home. This can include reinforcing walls, adding support beams, or even excavating for additional foundation work. The complexity of these structural changes will influence both the time and cost of your project.

Temporary Housing

If your home becomes uninhabitable during construction, you may need temporary housing, which can add to the cost.

Eco-Friendly Considerations

If sustainability and energy efficiency are priorities for your extension, investing in eco-friendly features can increase costs upfront but lead to long-term savings on utility bills. These features may include energy-efficient windows, insulation, and renewable energy sources.

Financing Options

Home Equity Loan

Many homeowners choose to finance their extension through a home equity loan, which provides a lump sum with a fixed interest rate.

Personal Savings

Using your personal savings to fund the project can save you on interest payments, but it may deplete your savings.


Determining the cost of an extension project involves considering various factors, including the project’s scope, architectural design, planning permissions, materials, labor, structural work, interior finishes, project timeline, and contingency budget.

By carefully evaluating these elements and making informed decisions, you can create a budget that aligns with your goals and ensures a successful extension project.

Remember that the cost of an extension can vary widely based on your specific requirements and location. It’s essential to consult with professionals, obtain multiple quotes, and plan meticulously to achieve the desired outcome within your budget.


1. Can I get an exact cost estimate before starting the project?

It’s challenging to provide an exact cost estimate upfront, as several variables can impact the final cost. However, contractors can provide a ballpark figure based on your project’s scope.

2. How long does a home extension project typically take?

The duration of a home extension project depends on its complexity and size. On average, it can take several months to complete.

3. Are there ways to reduce the cost of a home extension?

You can reduce costs by carefully planning your project, choosing cost-effective materials, and getting multiple quotes from contractors to find competitive prices.

4. Do I need planning permission for a home extension?

In many cases, you will need planning permission for a home extension. It’s essential to check with your local authorities to ensure compliance with regulations.

5. Should I hire an architect for my home extension project?

Hiring an architect can help you design a functional and aesthetically pleasing extension. Their expertise can also ensure that the project complies with building codes and regulations.

Author Profile

Mark Cullen
Mark Cullen
I have many qualifications and certificates in construction, such as City & Guilds, CPCS and CITB. These are the highest standards of training and competence in the industry. Whether you need help with plumbing, carpentry, bricklaying or any other trade, I’m here to help you succeed.