How Much Does a House Extension Cost in the UK? | 2026 Guide

One of the first questions homeowners ask when considering an extension is: how much will it cost?

The honest answer is that costs can vary significantly depending on the size, design and complexity of the project. However, understanding typical ranges can help you plan more effectively.

Typical extension costs

As a rough guide in the UK:

• Basic extensions: £1,500 – £2,500 per m²
• Mid-range extensions: £2,500 – £3,500 per m²
• High-end projects: £3,500+ per m²

These figures can vary depending on location, specification and site conditions.

What affects the cost?

Several factors influence the final cost:

• Size and layout of the extension
• Ground conditions and structural work
• Quality of materials and finishes
• Access to the site
• Design complexity

Hidden costs to consider

In addition to construction, you may also need to budget for:

• Architectural drawings
• Planning applications
• Structural engineering
• Building regulations
• Interior finishes

Why early advice helps

Many homeowners either underestimate or overestimate costs at the start.

Getting professional advice early can help you:

• Set a realistic budget
• Understand what’s achievable
• Avoid costly redesigns

A consultation can give you a clearer picture of what your project is likely to involve before you commit financially.

If you’re unsure how this applies to your own home, a Home Doctor consultation can help you understand your options.