Home extension London projects continue to rise in popularity as homeowners look for smarter ways to create more living space without the cost or stress of moving. Whether it’s a growing family, the need for a larger kitchen, or the desire to boost property value, extending your home in the capital is one of the most rewarding investments you can make.
However, the one question everyone asks first is simple: How much does it actually cost?
With construction prices fluctuating across the UK, clear and up-to-date information is essential. This detailed 2025 cost guide explains exactly what you can expect to pay at different budget levels, what influences the final price, and how to plan your extension wisely. HM Construction, a trusted name in home extensions UK, provides this guide to help homeowners make confident and informed decisions.
What Affects Home Extension Costs in London?
Before diving into cost brackets, it’s important to understand the key factors that influence pricing. London is unique demand is high, space is limited, and labour rates tend to be higher than elsewhere in the country. Here’s what shapes your total extension cost:
Location & Property Type
The style of your home whether it’s terraced, semi-detached, or detached affects everything from required structural work to accessibility. Terraced homes often involve more logistical planning, while detached properties offer greater flexibility.
Size & Layout of the Extension
Naturally, the larger the footprint, the higher the total cost. A simple rear kitchen extension will cost significantly less than an L-shaped wrap-around extension covering two sides of the house.
Materials & Specifications
Your chosen finish can have a major impact on pricing.
- Basic: standard kitchen units, laminate flooring, simple lighting.
- Mid-range: stone countertops, engineered wood flooring.
- High-end: bespoke joinery, aluminium bi-fold doors, premium tiling.
Your materials define whether you land in a low, mid, or high budget bracket.
Labour Costs in home extension London for 2025
London has some of the highest labour rates in the UK. Skilled trades like electricians, carpenters, and plumbers are in high demand, contributing to higher project costs compared to other regions.
Planning Permission & Building Regulations
Most rear home extensions fall under permitted development, but others require full planning permission. You may also need structural calculations, building control approval, and compliance checks—all of which add to your total spend.
2025 Cost Breakdown: Low, Medium & High Budget Levels
To make things clearer, HM Construction divides costs into three simple levels—low, medium, and high. These figures represent typical London rates per square metre.
Low-Budget Home Extension London (£1,800 – £2,200 per m²)
Low-budget builds are functional and cost-effective. These usually include simple layouts and standard finishes.
What’s included:
- Standard brickwork
- Basic insulation
- Simple PVC windows/doors
- Laminate flooring
- Basic electrical and plumbing setups
Suitable for:
- Small kitchen extensions
- Compact rear extensions
- Budget-conscious families
- Landlords upgrading rental properties
If you’re looking for practical space without the luxury elements, this budget offers excellent value.
Medium-Budget Home Extension London (£2,300 – £2,800 per m²)
This is the most popular bracket for home extension London. It offers a balance of quality, comfort, and modern design ideal for family homes.
Common features:
- Higher-quality insulation
- Modern kitchen fittings
- Engineered wood or porcelain flooring
- Stylish lighting options
- Aluminium sliding or bi-fold doors
Best for:
- Open-plan kitchen-diners
- Rear home extensions with glazing
- Side-return extensions
- Home offices or guest rooms
If you’re exploring home extension ideas, this budget gives you room to create something genuinely impressive.
High-Budget Home Extension London (£2,900 – £3,800+ per m²)
High-end extensions are premium-level builds designed for luxury living. These often involve architectural creativity, bespoke finishes, or complex structural elements.
Includes:
- Bespoke kitchens
- High-end materials (marble, quartz, hardwood)
- Smart home integration
- Roof lanterns or full glass walls
- Underfloor heating
- Premium aluminium frames
Ideal for:
- Double-storey wrap-around builds
- Luxury kitchen extensions
- Glass extensions
- High-value property refurbishments
If you’re aiming for maximum property value and superb design, this bracket is the best fit.
Popular Types of Home Extension London & Their Costs
Different layouts come with different complexities. Here’s what you can expect for the most requested extension types:
Single-Storey Rear Extension
Most common and cost-effective option.
Typical cost: £40,000 – £70,000 depending on size and finish.
Perfect for kitchen-diner transformations and creating open-plan living spaces.
Side-Return Extension
A favourite for Victorian and Edwardian homes.
Typical cost: £55,000 – £90,000.
Often used to widen narrow kitchens and bring in natural light.
Double-Storey Extension
More complex but great for adding extra bedrooms.
Typical cost: £80,000 – £140,000+.
Adds major value to your property.
Wrap-Around Extension
A combination of rear + side return.
Typical cost: £90,000 – £160,000+.
Ideal for creating a large open-plan family space.
Kitchen Extension
Whether modest or luxurious.
Typical cost: £45,000 – £100,000+.
Costs vary widely depending on kitchen specification.
Additional Costs You Should Expect
Architectural Drawings
£1,200 – £3,500 depending on complexity.
Structural Engineer Fees
£600 – £1,500.
Planning Permission
£250 (if required).
Party Wall Agreements
£1,000 – £2,000 per neighbour.
Utilities & Services
Rewiring, plumbing, boiler upgrades £1,500 – £10,000.
Finishing & Decoration
£2,000 – £10,000 depending on choice.
How to Calculate Your Home Extension Cost (Simple Formula)
A quick estimate formula:
Cost = Size (m²) × Cost per m²
Example 1 – 20m² low-budget extension:
20 × £2,000 = £40,000
Example 2 – 25m² mid-range extension:
25 × £2,600 = £65,000
Example 3 – 30m² high-end extension:
30 × £3,200 = £96,000
Use this to assess affordability and compare options quickly.
Money-Saving Tips for Home Extension London (2025)
- Choose efficient design: A simple rectangular layout is cheaper than complex shapes.
- Consider phased decoration: Focus on the build first, and finish later.
- Reuse elements where possible: Existing foundations, utilities, or structural walls.
- Pick materials wisely: Engineered wood over hardwood, composite over aluminium.
- Work with a design-and-build team: HM Construction reduces delays, errors, and extra costs.
A well-planned design saves thousands before construction even starts.
Why Choose HM Construction for Your Home Extension?
HM Construction is known across London for its reliable craftsmanship, transparent pricing, and commitment to customer satisfaction. With years of experience delivering home extension London UK, the team specialises in everything from small rear extensions to large bespoke builds.
What you get with HM Construction:
- Full design-and-build service
- Clear cost breakdowns
- High-quality workmanship
- Guidance on planning and regulations
- Consistent communication from start to finish
Whether you’re exploring simple home extension ideas or planning a large-scale transformation, HM Construction ensures your home extension London is built to last.
Conclusion
Extending your London home in 2025 is an excellent way to add space, comfort, and value especially with rising property prices. Whether your budget is low, medium, or high, there is a practical solution for every homeowner. With the right planning, clear cost expectations, and the support of a trusted construction partner like HM Construction, your dream extension can become a reality.
If you’d like personalised guidance, planning support, or a free quotation, HM Construction is ready to help you every step of the way.
FAQs
How much do home extension London cost?
From £1,800 per m² depending on design and finish.
Do I need planning permission?
Only for larger or complex extensions.
How long does an extension take?
Most take 8–14 weeks to complete.
What is the cheapest extension type?
A small single-storey rear extension.
Are home extensions worth it?
Yes, they add value and usable space.
Can I live at home during the build?
Yes, for most single-storey projects.
What adds to extension costs?
Materials, labour, size, and structural work.
Do I need architectural drawings?
Yes, for planning and structural safety.
How do I estimate my extension cost?
Multiply size (m²) by cost per m².
Why choose HM Construction?
They offer reliable, high-quality design and build services.
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