How Much Does a House Extension Cost in London (2025 Guide)

Written by Dario | Jun 20, 2025 9:09:47 AM

Thinking about a house extension in London? This guide will help you understand what you could spend in 2025 and how to plan smartly from the start.

Average House Extension Costs in London for 2025

In 2025, the average cost of a house extension in London ranges from £30,000 to £95,000. This depends on the type of extension, size, materials, and location within Greater London. The capital often sees a higher cost per square metre due to planning complexity and labour rates.

  • Rear extensions: £30,000 to £60,000
  • Side return extensions: £40,000 to £70,000
  • Wrap-around extensions: £65,000 to £95,000

These estimates include design, materials, and labour but exclude VAT and unexpected structural works.

Factors That Influence Your Extension Costs

No two extensions cost the same. Key factors include:

  1. Property type – Period homes may require specialist works.
  2. Planning permission – Complex applications raise design and planning fees.
  3. Access – Tight sites or restricted access can slow down work.
  4. Finish level – Bespoke kitchens and luxury flooring increase final totals.

Always budget at least 10% as a contingency to avoid stress when surprises arise.

Planning Ahead for Your 2025 Build

London councils continue to prioritise sustainable and low-impact design. Start early by checking:

  • Whether your project qualifies under permitted development
  • Conservation area or listed building constraints
  • How neighbours might impact your party wall agreements

Investing in planning now means fewer delays and better cost control later.

Who to Trust with Your House Extension

Choosing the right team is one of the biggest cost-saving decisions you can make. Inexperienced or unlicensed builders often quote low and charge more later. A reputable contractor will offer:

  • Transparent pricing
  • Detailed breakdown of works
  • Strong communication and realistic timelines

Take time to understand their past experience and the types of projects they typically handle.

Saving Without Compromising on Quality

Saving money on extensions in London doesn’t mean cutting corners. Instead:

  1. Use off-the-shelf products for windows or kitchens
  2. Phase non-essential finishes until after construction
  3. Ask your contractor how to reduce waste or recycle site materials

Experienced contractors will help you invest wisely without hurting your vision.

Frequently Asked Questions

How much should I budget per square metre in London?

In 2025, costs in London range from £2,000 to £3,500 per square metre depending on complexity, materials, and finish level.

Do I need planning permission for a house extension?

Some extensions fall under permitted development rights, but this varies by borough. Always check with your local authority.

How long does a house extension take to complete?

Most projects take 3 to 6 months depending on size and whether planning is required.

Can I live in my house during the extension?

In many cases, yes. However, noise, dust, and safety may make temporary relocation advisable during structural stages.

Is VAT included in extension quotes?

Not always. Most quotes exclude VAT. Always ask for full pricing breakdowns upfront.

Final Thoughts

Planning a house extension in London is an investment. With the right knowledge and team, your project can stay on track and on budget. Share this guide if you found it useful or keep it handy for when you're ready to begin.
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