How Much Does a House Extension Cost in 2025? A Guide for Sussex, Surrey & Kent Homeowners

Cost is one of the first considerations to be made when planning your house extension. With house prices still high and the cost of moving on the rise, more people are choosing to remodel instead of relocate. A well-planned house extension can transform how you live - giving you the space you need without the upheaval of moving.

But how much does a home extension cost in 2025? In this guide, we’ll answer the questions you might have about the cost of a house extensions. We’ll break down the current average prices, explain what affects the cost, and help you budget smartly if you're planning an extension in Sussex, Surrey or Kent. We would recommend, as a good starting point, using our house extension cost estimator (for free!) to get a rough idea of costs - follow this link and scroll down

https://shieldbuild.co.uk/extensions

 What is the average cost per square meter for a house extension?

As of this year, here’s what you can expect to pay for a typical extension across Surrey, Sussex and Kent:

• Single-storey extension: approx. £2,500 per m²
• Double-storey extension: approx. £4,000 per m²

Keep in mind: costs in the South East tend to be slightly higher than the UK average due to local labour rates and materials.

 

What do I need to consider when budgeting for a house extension?

Not all extensions are priced the same—even if they’re the same size. Here’s what structural differences can affect the final cost:

•  Size and shape – Larger builds naturally cost more. Complex shapes (like L- shaped wraps) require more labour and materials.
•  Extension type – Single-storey extensions are cheaper than double-storey ones
•  Ground conditions – Poor access, sloping gardens, or clay soil can raise costs due to foundation challenges. 
•   Roof design – Flat roofs cost less than pitched roofs. Adding skylights increases spend.
• Glazing – Large bifold or sliding doors add light, but also cost more.
• Kitchen or bathroom fit-outs – High-end fixtures, tiling and plumbing can push the budget up.
• Access to the site – Limited rear access or tight driveways can slow down progress and increase labour time.

When budgeting for a house extension, it's also essential to consider more than just the construction costs. Other things to factor in are:

• Planning permission fees (if applicable)
• Architect or designer fees 
• Structural engineer costs      
•  VAT      
•  Site preparation 
• Accommodation or storage

 You should also account for any unexpected expenses, which can often arise during the build. A realistic, well-researched budget with a 10-15% contingency can help prevent costly surprises down the line.

 

What’s typically included in a house extension quote?

When reviewing a building quote, it’s important to check exactly what is—and isn’t—included. Ideally, you’ll want to work with a company that offers a comprehensive service, covering every stage of the extension process from design to completion. This should include architectural drawings, groundwork, and finishing touches such as painting, tiling, and fitting worktops. A full project management quote typically includes:

• Foundations and structure
• Planning or structural design fees
• Walls, roofing, windows, doors
• First fix electrics and plumbing
• Insulation and plastering
• Labour and project management
• Kitchen units, worktops, appliances
• Bathroom suites and fittings
• Tiling, flooring, painting and decorating

Always ask for a full itemised quote so you can clearly see what is and isn’t included.

 

How to save money without cutting corners

• Stick to a simple shape (square or rectangle)
• Choose a flat roof over pitched if design allows
• Keep plumbing work in the same location (e.g. extend kitchen without moving drainage)
• Reuse appliances if possible
• Plan everything early—making changes mid-build is costly
• Use a local, experienced builder who knows the regulations and can avoid expensive surprises

 

Why local expertise matter

Building regulations, planning rules and supplier costs vary depending on where you live. At Shield Build Ltd, we’ve been working on home extensions across Sussex, Surrey and Kent for over 20 years. We understand the local council requirements, ground conditions, and best-value suppliers—and we know how to deliver great results without overcomplicating things.

A house extension in 2025 can cost upwards of £30,000, depending on what you want to achieve. But done properly, it adds more than just value—it creates space, comfort, and a better way of living.

If you’re in the early planning stages, we’d love to help. We offer clear, detailed quotes and advice based on your specific home and goals—no hidden fees, no pressure. To help get you started on your journey with planning your house extension, we have an extension cost estimator on our website you can use for FREE - follow this link and scroll down:

https://shieldbuild.co.uk/extensions

 

Ready to Get Started?

Let’s talk about your extension plans.

Follow this link and scroll to the bottom of the page to fill out our contact form - https://shieldbuild.co.uk/extensions