London House Extension Costs 2025 | Vector Living Tips
- Vector Living
- Nov 9
- 7 min read
If you're considering a house extension in London, Surrey, or Hampshire in 2025, it's important to understand the costs, timelines, and approvals involved. A side return or rear kitchen extension can significantly enhance your living space, but costs can vary based on factors like design complexity, location, and materials. At Vector Living, we provide end-to-end project management, ensuring your extension is completed on time, on budget, and with minimal disruption to your family life. Read on for a comprehensive guide to house extension costs in 2025 and how Vector Living can help you achieve your dream extension.
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Why Extension Costs Look Different in 2025
The cost of house extensions in 2025 is influenced by several factors, including market trends, labour rates, and material availability. In London, prices have been impacted by inflation and the increasing demand for high-quality materials and skilled labour. Access to your property also plays a significant role, narrow streets, limited parking, and heritage locations can add premiums to the overall cost.
To keep your costs under control, we recommend conducting early surveys and setting a fixed scope to avoid budget creep. Having a clear design and budget from the start is essential for managing costs effectively.
Cost Drivers You Must Plan For
When budgeting for a side return or rear kitchen extension, several key cost drivers will influence the overall price.
Build Scope and Complexity:
Structural Openings and Steel Design: The size of the structural opening between your existing property and the new extension, as well as the steel design required to support the structure, can add significant costs.
Roof Type and Glazing: The choice of roof type and glazing, such as large glass doors or rooflights, can drive up costs. Glazing, in particular, can be expensive, but it’s crucial for creating a bright, airy space.
Services Upgrades: Your kitchen and utility areas may require electrical and plumbing upgrades to handle the demands of modern appliances. This can add to the overall budget.
Specification Choices:
Kitchen, Worktops, and Appliances: The choice of kitchen units, worktops, and appliances will have a significant impact on your budget. High-end materials and appliances can push costs up, but they also improve functionality and aesthetics.
Flooring, Heating, and Lighting: The type of flooring, heating system, and lighting fixtures you choose will all contribute to the cost. Underfloor heating, for example, adds both to the cost of materials and installation time.
Joinery and Bespoke Storage: Custom-built joinery and storage solutions are excellent for optimising space in your extension but can be expensive compared to off-the-shelf options.
Site Constraints and Access:
Scaffolding and Deliveries: On narrow streets, scaffolding and delivery vehicles may require permits or special arrangements, which can add to the overall cost.
Temporary Works and Protection: For properties in close proximity to neighbours, you may need to invest in temporary works or protection to prevent damage to shared walls and ensure safe working conditions.
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Side Return Extension Cost Guide London 2025
A side return extension is a popular choice for creating an open-plan kitchen-dining space. The typical footprint for a side return extension is 3-4 metres wide, which makes a significant difference to kitchen layout and flow.
Build Cost per m² London: In 2025, the average cost for a side return extension in London is between £2,000 and £3,000 per m², depending on the specification and complexity.
Drainage and Party Wall Works: You’ll also need to budget for drainage works and potentially a party wall agreement, especially in terraced homes, where the extension might impact shared walls.
Value Options: You can manage costs by opting for standard rooflight options rather than full-glass structures, which are more expensive but can add significant visual appeal.
Rear Kitchen Extension Cost Guide London 2025
A rear kitchen extension typically involves creating a larger living space with an opening to the garden, which enhances both natural light and indoor-outdoor flow.
Build Cost per m² London: The average cost for a rear kitchen extension in London is between £2,500 and £3,500 per m², depending on the materials and the complexity of the build.
Structural Knock-Through and Bifolds: This type of extension often includes the cost of structural knock-throughs and the installation of large bifold doors or sliding doors, which can add £10,000 or more to your budget.
Planning and Buildable Depth Limits: When extending a rear kitchen, it’s important to consider local planning restrictions, particularly around how far you can extend into the garden. Some boroughs have limits on buildable depth, which could affect your design and costs.
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Professional and Statutory Fees in London
In addition to the construction costs, there are several professional and statutory fees that you must account for in your extension budget.
Planning Permission Costs and Alternatives:
Planning Application Fees: If your extension requires planning permission, you’ll need to pay for application fees, which can range from £200 to £400, depending on your local council.
Lawful Development Certificate (LDC): For certain projects, especially those under permitted development, an LDC may be required. This typically costs between £100 and £200.
Conservation Area Considerations: If your property is in a conservation area, additional costs for compliance may be necessary, and planning approval might take longer to secure.
Party Wall Costs and Process:
Party Wall Surveyor Fees: If your extension affects a shared wall or boundary, you’ll need to engage a party wall surveyor. Fees for this process can vary but typically start at around £1,000.
Shared Wall Steel Bearings: In cases where structural steel beams need to bear onto shared walls, you’ll need to account for additional costs, including engineering calculations and specialist labour.
Building Control and Structural Engineering:
Plan Check and Inspections: Your extension will need to be approved by building control, and this process includes multiple inspections during construction to ensure compliance with building regulations.
Calculations for Beams and Foundations: Depending on the complexity of your extension, you may need structural engineering calculations for beams, pads, and foundations, which will add to your costs.
Programme and Timelines to Site Start 2025
Timing is crucial for a successful extension project, especially if you’re working around family milestones or wanting to complete before a certain season.
Typical Sequence for a Smooth Build:
Month 0 to 1: Measured survey and concept design.
Month 1 to 2: Planning or LDC submission.
Month 2 to 3: Technical design and tendering process.
Month 3 to 4: Procurement and mobilisation.
Indicative Site Durations: Side return extensions typically take 3 to 4 months to complete, while rear kitchen extensions may take 4 to 6 months, depending on the complexity and materials.
Build Cost per m² London Guidance
Understanding the cost per m² is key to setting a realistic budget for your extension. Here’s a breakdown for typical good, better, and best specifications:
Good Spec: £2,000 to £2,500 per m² – Standard materials and finishes, including basic kitchen units and flooring.
Better Spec: £2,500 to £3,000 per m² – Higher-end materials, including quality kitchen appliances, underfloor heating, and premium glazing.
Best Spec: £3,000 to £3,500 per m² – Custom designs, high-end appliances, and luxury finishes such as bespoke joinery and large glass doors.
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Ways to Optimise Budget Without Compromise
There are several ways to optimise your budget without sacrificing quality:
Value Engineering Moves:
Standardise Spans and Glazing Modules: Opting for standard structural spans and glazing sizes can significantly reduce costs.
Efficient Heating and Lighting: Choosing energy-efficient heating solutions and lighting packages can lower both your initial costs and long-term energy bills.
Bundle Kitchen Procurement: Purchasing your kitchen as part of the main contract can save money compared to buying separately.
Avoidable Cost Risks:
Late Scope Changes: Delays or changes to the design during construction can cause budget overruns. Ensure that scope and decisions are locked in early.
Underestimating Utilities Upgrades and Drainage: It’s easy to overlook the cost of drainage or utility upgrades, but they can be a significant cost in a rear kitchen extension.
Vector Living Delivery Approach
At Vector Living, we ensure that your extension project runs smoothly from start to finish.
Our approach includes:
Single Point of Contact: One dedicated project manager handles all communication, ensuring transparency and clarity throughout the process.
Transparent Cost Plans: We provide clear cost breakdowns and staged approvals to keep you informed.
Trusted Trades and Sequenced Works: Our qualified contractors are familiar with our process, ensuring that your extension is delivered on time, on budget, and with minimal disruption.
Ready to start planning your house extension? Book a free 20-minute discovery call with Vector Living today to discuss your side return or rear kitchen extension project. Let us help you create the home you’ve always wanted, with clear costs and a managed timeline.
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FAQs About London Extension Costs 2025
What is the quickest way to get a costed proposal?
Start with a measured survey and outline scope for pricing. This will give you a clear idea of the project’s costs.
Do I need planning permission for a rear kitchen extension?
Many single-storey rear extensions can proceed under permitted development. Confirm with a Lawful Development Certificate and local policies.
What budget should I allow for party wall matters?
Set a realistic allowance for surveyors and awards, especially in terraced and semi-detached properties.
How is build cost per m² calculated in London?
It is based on the gross new floor area and the specification level, including optional items like kitchens, glazing, and landscaping.
How long will my extension take on site?
Side returns are typically faster to complete than deep rear kitchens. Duration depends on structure, access, and finish level.
Questions, or ready for a site visit?
Get a free quote, 0208 058 8008 or office@vectorliving.co.uk
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