How Much Does a House Extension Cost in 2025?

One of the first questions we hear from clients considering a home extension is simple and important:

How much will it cost?

The answer, as you might expect, depends on many factors. But with construction costs, material prices, and energy efficiency standards continuing to evolve, it's more important than ever to go into your project with realistic, up-to-date expectations.

Here’s what you need to know about house extension costs in 2025 and how to plan wisely.

Average Extension Costs in 2025 (UK)

As a rough starting point, here are typical build costs per square metre:

•  Basic quality extension: £2,200 to £2,600 per m²

•  Mid-range quality: £2,600 to £3,200 per m²

•  High-end or bespoke: £3,200 to £4,500+ per m²

  
  

So for a 30m² rear extension, you're likely looking at a starting point of £66,000 for a basic build, or £96,000+ for something tailored, considered, and finished to a higher standard.

Keep in mind: these are build costs only. They do not include VAT, professional fees, kitchen fittings, glazing upgrades, or landscaping.

What Affects the Price of Your Extension?

Several key factors will influence your overall costs:

1. Type of Extension

•  Rear or side return extensions tend to be more straightforward and cost-effective

•  Wrap-around or two-storey extensions introduce more complexity and structural work

•  Loft conversions may be cheaper per m² but can add complexity if major alterations are needed

  
  

2. Specification and Materials

The quality of finishes, choice of materials, bespoke joinery, feature glazing, and sustainability targets all have a huge impact.

3. Site Conditions

Is access easy? Are there trees, levels, or drainage concerns? Is the home in a conservation area or listed? These hidden conditions can affect both cost and timeline.

4. Planning and Permissions

Some extensions fall under permitted development rights, while others require full planning consent. Projects in conservation areas or involving listed buildings may require additional surveys or specialist reports.

5. Professional Fees

Don’t forget to budget for:

•  Architect’s fees

•  Planning application fees

•  Structural engineer

•  Party wall surveyor

•  Building control

•  VAT (typically 20%, unless exemptions apply)

Professional fees can range from 12% to 20% of the overall construction cost, depending on the complexity and level of service.

Have You Checked for Legal Constraints?

Before getting too far into planning, it's important to understand any legal restrictions on your land.

•  Easements, such as shared access or drainage routes

•  Rights of way, which may limit how or where you can build

•  Restrictive covenants, which might prohibit certain alterations or extensions
  

These are often hidden in the title deeds and can significantly influence what is or isn’t possible on your plot.

If you're unsure, now is the time to request the most recent title documents and consult a solicitor or your architect. Addressing these early can save time, money, and frustration later on.

Are Prices Still Rising in 2025?

In 2024, the construction industry saw modest inflation on materials, alongside stabilised

labour costs in some regions. For 2025, many builders are quoting with more confidence.

However, with continued demand for energy-efficient upgrades, supply chain challenges in

specialist materials, and regional labour shortages, prices remain above pre-2020 levels.

That said, with good planning and an experienced team, many of these costs can be

forecast and managed effectively.

How to Make the Most of Your Budget

At TerraForma, we believe design should work with your budget, not against it. Here’s how we help clients maximise value:

•  Early-stage cost planning to ensure your vision aligns with reality

•  Design-led solutions that make the most of space, light, and materials without unnecessary complexity

•  Collaboration with contractors to develop efficient build strategies

•  Advice on VAT relief and phasing, especially for energy upgrades or listed buildings

Ready to Explore What’s Possible?

A well-designed extension can completely transform how your home feels and functions. But it starts with clear, honest conversations around budget, priorities, and constraints. If you're planning to extend your home in 2025 and want a team who will guide you with care and clarity, get in touch for a free initial call.

Let’s make your space work better, beautifully, sustainably, and within budget.

Get in touch