How Much Does a House Extension Cost in London?

Are you considering extending your home in London? This comprehensive guide breaks down the costs, tax considerations, consultant fees, and practical advice to help you make informed decisions, maximise your budget, and achieve your dream living space.

Why Extend Your Home?

Building a house extension can be a more economical and less stressful alternative to moving, especially in a fast-paced city like London. Beyond cost savings, extensions offer the opportunity to tailor your home to your needs and create a space that works perfectly for you. However, it’s important to note that house extensions in London typically carry a cost premium compared to other areas in the UK. This is due to higher labour and material costs, as well as the logistical challenges posed by compact construction sites and restricted access.

Burrows Road Glazed Envelope in Kensal Rise, NW London

House Extension Costs in 2024

The cost of your extension will largely depend on its size, as this directly correlates to the overall budget. Below are estimated costs for construction (updated for 2024 and including a 7% increase), excluding VAT and professional fees:

Single-Storey Extensions

• London: £2,355–£3,530 per sqm
  For cost-effective finishes, budget around £2,355 per sqm. High-end finishes will increase costs to £3,530 per sqm.
• Rest of the UK: £1,410–£1,765 per sqm

Two-Storey Extensions

Add 50–60% to the single-storey costs. Economies of scale apply, as only one set of foundations and a single roof structure are required, but planning permissions may be more challenging.

Basement Extensions

Basement extensions are significantly more expensive due to the complexities of construction and associated risks:

• London: £4,705–£5,880 per sqm

Twelve Arches, Kensal Rise, NW London

Key Cost Factors

Functionality

• Kitchens: Adding a kitchen to your extension typically costs an extra £16,000–£42,800, depending on the design and appliances.
• Bathrooms: Expect to pay £5,350–£10,700, increasing with higher-quality fixtures and finishes.

Site Constraints

• Difficult access (e.g., terraced houses) can increase costs as builders may add charges for moving materials and equipment.
• Site-specific challenges such as soil conditions, relocating utilities, or removing existing structures (e.g., conservatories or sheds) will also add to your budget.
• Extensions for listed buildings or properties in conservation areas will incur higher consultant and construction fees.

Specifications

• Larger windows and bespoke glazing (e.g., bi-fold or sliding doors) significantly enhance a project but will increase costs.
• Flooring, tiling, smart home systems, and lighting will also impact your budget.

Additional Costs to Consider

Consultant Fees (15–20% of Construction Costs)

• Architects: Architects are central to any extension project. They provide design expertise, help navigate planning permissions, and ensure your vision is realised in a way that works within your budget.

  Architects can also identify cost-saving solutions, such as reorganising existing spaces, and produce detailed drawings to reduce the risk of costly on-site errors.

• Other Consultants: Quantity surveyors and structural engineers may be required, depending on the complexity of your project.

Planning and Administration

• Planning applications for house extensions cost £206.
• If your extension falls under permitted development, applying for a Lawful Development Certificate (£103) is highly advisable. This certificate confirms the work is lawful, which is particularly important for resale purposes.

VAT

Extensions generally attract a 20% VAT rate. However, properties vacant for two or more years may qualify for a reduced 5% rate. Your architect can guide you through VAT exemptions or reductions.

Insurance

Your standard home insurance policy may not cover you during construction. Additional policies, such as non-negligence insurance, can protect you against unforeseen damages to your property or neighbouring properties.

Queen's Park House, Queen's Park, NW London

Budget Breakdown

Here’s an approximate breakdown of a typical project budget:

• Construction: 60%
• Architect: 10% (part of the 15–20% consultant fees)
• Other Consultants: 5%
• Planning and Admin: 1%
• Party Wall Agreements: 3%
• Insurance: 1%
• VAT: 20%

How Architects Can Help

A good architect doesn’t just design your space - they manage your project to ensure efficiency, cost-effectiveness, and a high-quality outcome. They can:

• Advise on cost-saving alternatives.
• Provide detailed plans for accurate builder quotes.
• Help navigate planning permissions and potential site constraints.
• Recommend builders and oversee the construction process to ensure smooth execution.

Ice Cream House, Hampstead, N London

Added Value

Beyond the practical benefits, a well-designed extension can increase the value of your home by up to 30%, particularly in sought-after areas of London. Additionally, tailored spaces, such as garden-linked kitchens, home offices, or playrooms, can significantly enhance your lifestyle and make your home more enjoyable.

Frequently Asked Questions

Do I Need a Quantity Surveyor?

A quantity surveyor is advisable for projects exceeding £100,000. They provide accurate cost estimates, break down your budget, and help you identify savings.

What Are the Timeframes for a House Extension?

The timeline depends on the complexity of the project, but you should plan for 6–12 months, including design, planning, and construction.

How Much Space Should I Add?

The size of your extension should balance your needs, budget, and potential planning constraints. Your architect will help you determine the optimal size for your property.

Ready to transform your space? At RISE Design Studio, we specialise in sustainable, client-focused design, helping you craft a beautiful and functional extension that enhances your home and enriches your lifestyle. Whether you're dreaming of a double-storey extension to create more room for family, work, or leisure, we’re here to bring your vision to life in 2024.

Let us help you design a space that not only adds value to your property but also aligns with your aesthetic and practical needs. Get in touch with us today to start your journey towards a more spacious and inspired home.