What Does a House Extension Cost in London? (2025 Guide)

Everything You Need to Budget for a Home Extension in London

Adding extra space to your home is one of the smartest ways to improve your lifestyle and increase property value — especially in London, where moving costs are sky-high. But one of the first questions homeowners ask is: how much does a house extension cost in London?

In this guide, we break down the key cost factors, average prices, and tips for planning your extension budget in 2025.

Average House Extension Costs in London (2025)

Type of Extension	Average Cost per m²	Total Estimate (20m²)
Basic Single-Storey	£2,000 – £2,500	£40,000 – £50,000
Mid-Range (with kitchen/bathroom)	£2,500 – £3,000	£50,000 – £60,000
High-End / Bespoke	£3,000 – £4,000+	£60,000 – £80,000+
Double-Storey	50–60% more than single-storey	From £65,000+

Prices vary depending on design, materials, access, and finish level.

What Affects the Cost of a House Extension in London?

1. Size & Complexity

Larger or more complex builds (like wraparound or L-shaped extensions) increase both labour and materials cost.

2. Design & Architecture

Custom architectural designs or modern features like bi-fold doors, skylights, or open-plan layouts will raise the budget.

3. Kitchen or Bathroom Installations

Including plumbing, tiling, electrics, and appliances can add £8,000–£20,000+, depending on quality.

4. Ground Conditions & Access

Tight access, sloped land, or drainage issues may require additional groundwork or specialist machinery.

5. Planning Permission & Fees

• Planning permission (if needed): £206 (standard UK fee)

• Architectural drawings: £1,500–£3,000+

• Structural calculations: £500–£1,200

• Party Wall Agreement: £1,000–£2,500 (if needed)

Do You Need Planning Permission for a House Extension in London?

In many cases, Permitted Development (PD) rights allow you to build without formal permission, if you meet certain size and location rules.

You will need planning permission if:

• You live in a conservation area or listed property

• The extension is too large for PD rules

• You’re building near a boundary or highway

At Morphos Group Ltd, we guide you through all planning steps and handle submissions.

How Long Does a House Extension Take in London?

Stage	Time Estimate
Design & Planning	4–8 weeks
Planning Permission (if needed)	8–10 weeks
Construction	10–16 weeks depending on complexity

Total time: 3–6 months from start to finish.

Types of House Extensions & Costs

🔹 Rear Extension (Most Common)

Perfect for kitchen-diners or open-plan living.

• Cost: £40,000 – £70,000+

🔹 Side Return Extension

Great for narrow London terraces.

• Cost: £30,000 – £60,000+

🔹 Wraparound Extension

Combines rear + side for maximum space.

• Cost: £65,000 – £100,000+

🔹 Double-Storey Extension

Adds extra bedrooms or bathrooms above.

• Cost: £75,000 – £120,000+

Cost-Saving Tips

• Use existing plumbing lines where possible

• Choose standard-sized windows/doors

• Minimise steelwork by sticking to load-bearing wall locations

• Go for a design & build contractor to streamline the process and save on architectural fees

Final Thoughts

A house extension in London is a major investment — but one that adds real, lasting value to your property. With the right team and a clear budget, you can transform your home without overspending or delays.

Get a Free Quote for Your House Extension

At Morphos Group Ltd, we provide end-to-end house extension services across London — including planning, architecture, structural works, and finishes.

Call us today or request a free site survey online.