HOW MUCH DOES A HOME EXTENSION COST IN THE UK IN 2025?

Thinking about extending your home? Whether it is a bigger kitchen, a light filled garden room or an extra bedroom, a well designed extension can completely transform the way you live. One of the most common questions we hear from homeowners is: how much does a home extension really cost in 2025?

The answer depends on a few key factors such as size, location, specification and complexity. This guide explains real world figures, what affects costs and how to plan a realistic budget with confidence.

Average Extension Costs per Square Metre in 2025

Here is a helpful guide to typical build costs in the UK this year:

Quality Level	Approximate Cost per m²
Basic build quality	£1,800 to £2,400
Mid range (most common)	£2,500 to £3,500
High end or complex design	£3,500 to £4,500 plus

In London and the South East or for high specification and bespoke finishes, costs may go above £5,000 per square metre.

Example: A 25 square metre rear extension at mid range quality might cost between £62,500 and £87,500 for construction only.

What Else Should You Budget For?

The build cost is only one part of the total. Here are typical additional costs to include when planning your extension:

Item	Typical Cost
Architectural design	6 to 12 percent of construction cost
Structural engineer	£800 to £2,000
Planning application	£528 for planning, or around £150 for a lawful development certificate
Building Control	£500 to £1,200
VAT	Usually 20 percent
Interior finishes and furniture	Highly variable depending on taste and quality

It is a good idea to include a contingency fund of 10 to 15 percent for any unexpected costs.

Example Budget for a 25m² Extension

Here is a realistic example of a 25 square metre ground floor extension using mid range finishes:

Item	Estimated Cost
Construction	£70,000
Architect and Designer	£6,000
Structural Engineer	£1,500
Planning and Building Control	£1,000
Kitchen and Interior Works	£20,000
Contingency (10 percent)	£9,500
Total Estimated Cost	£107,500

This gives a more complete picture of overall investment rather than just build cost alone.

What Affects Extension Costs the Most?

Complexity of design

Large openings, steel supports, skylights and bespoke glazing can add cost but often add significant value too.

Level of finish

Standard kitchen or bespoke? Vinyl flooring or oak? Lighting, storage and joinery can easily change the overall budget.

Location

London and the South East are the most expensive areas. Scotland, Wales and the North of England often offer better value.

Planning and site access

Homes in conservation areas, sloping sites or restricted access locations may require additional work or approvals.

Are Costs Rising in 2025?

Construction prices have stabilised after steep rises in recent years. Supply chains are more consistent and costs are becoming more predictable. This makes 2025 a good year to plan ahead and secure builder availability.

How to Keep Your Budget on Track

• Work with an architect to design with cost awareness

• Avoid making design changes once on site

• Get fully detailed drawings and specifications before requesting quotes

• Make sure builder quotes are comparable and itemised

• Remember that the lowest quote is not always the best value

Final Thought

A well planned extension is more than extra space. It can create better daily living, improve natural light and increase the value of your home. Understanding the true cost is the first step to making confident decisions.

If you would like help exploring design ideas, planning or feasibility, we would love to chat.

Book a friendly consultation with Nua Architecture and Interior Design.