Estimated Extension Costs for 2025: Planning Your Budget with Our Useful Guide
Planning to extend your home? Here's a comprehensive guide to help you understand the costs involved in building extensions in the UK in 2025.
Single-Storey Extensions
The cost of a single-storey extension can range from around £22,500 to £125,000, depending on size, location, and the quality of finish. For a small 15m² extension, expect to pay between £22,500 and £37,500, with London and the South East being at the higher end due to labour costs.
Side Return Extensions
Side return extensions typically cost between £35,000 and £55,000 for a 4m x 2m extension, depending on location and finish. An approximate figure for a side return extension should be around £2,800-£3,100 per m² (excluding VAT).
Two-Storey Extensions
Two-storey extensions generally cost 50% to 75% more than single-storey extensions due to additional complexities like foundations, roofing, plumbing, and electrical work. Exact UK-specific figures are less detailed, but expect significantly higher costs than single-storey extensions.
Conservatory Extensions
Conservatory extensions often cost less than full extensions but vary widely depending on materials and style. While specific costs were not provided, conservatories might be at the lower end of the extension cost spectrum.
Kitchen Extensions
Kitchen extensions (often single-storey) cost from around £50,000 to £120,000 depending on size, complexity, materials, and location. Structural costs alone range from roughly £2,200 to £3,300 per m² in 2025.
Factories Prefabricated Timber Frame Extensions
Factory prefabricated timber frame extensions have a cost range of £2,200-£2,800 per m², have factory quality control, faster on-site assembly, better air-tightness, but have higher upfront costs, less design flexibility, and require access for delivery.
Concrete Blockwork Extensions
Concrete blockwork extensions have a lower cost option of £1,600-£2,000 per m², are familiar to builders, good for DIY projects, but have a basic appearance that needs finishing, are weather dependent, and have lower thermal performance.
SIPs (Structural Insulated Panels) Extensions
SIPs extensions have a cost range of £2,400-£3,000 per m², offer excellent thermal performance, quick assembly, and reduced labour costs, but have higher material costs, require specialist installation, and have limited design flexibility.
ICF (Insulated Concrete Formwork) Extensions
ICF extensions have a cost range of £2,300-£2,900 per m², have good thermal performance, quick construction, and all-weather building, but are a specialist system, have higher material costs, require experienced contractors, and are less flexible in design.
Oak Frame Extensions
Oak frame extensions have the highest cost option of £3,500-£4,500 per m², offer a premium appearance, long lifespan, and are an architectural feature, but require specialist design, have limited suppliers, and are less common.
Self-Managed Extensions
Self-managed extensions, where you act as the project manager and hire individual trades, offer good potential for cost control and have a medium risk level.
Extension Insurance Requirements and Costs
Extension insurance requirements and costs include notifying your existing home insurance provider of the works, additional coverage being usually required, and total insurance costs between £1,500-£3,000 for a typical £100,000 extension.
Building Control Fees
Building control fees for extensions can vary, with typical fees for private building control being £630-£1,200 for a typical extension, which includes plan checking, site inspections, and a final inspection for certification.
Additional Expenses
When budgeting, don't forget to factor in additional expenses such as temporary kitchen facilities during construction, garden landscaping costs post-build, and any new furniture and appliances you'll need.
For a typical 30m² kitchen extension, budget between £66,000-£99,000 plus VAT.
Choosing the Right Construction System
Choosing the right construction system for your extension depends on your budget, site constraints, and local builder availability. Modern systems like SIPs and ICF might cost more initially, but can save weeks on build time and are worth considering if you're paying rent during construction or are worried about how long an extension takes.
Project Management
The cost of a two-storey extension per square metre is usually lower because you're spreading the cost of foundations and roof over twice the floor area. How you choose to run your project will also have a significant impact on the cost. Choosing a main contractor for the project inevitably incurs a higher overall build cost.
DIY Route
The DIY route for extensions can result in the highest potential savings, but requires a significant time commitment, good project management skills, and carries the most risk.
Always factor in a contingency of at least 10% for unexpected issues, and consider adding another 5% for potential inflation impacts. Also, consider whether you can face living on site during the build or need to move out for some or all of the duration of the project.
- The cost of a single-storey extension can range from £22,500 to £125,000, depending on factors like size, location, and quality of finish.
- Ideas for potential finishing touches in your extension can be found in lifestyle, fashion-and-beauty, and home-and-garden magazines.
- Side return extensions typically cost between £35,000 and £55,000 for a 4m x 2m extension, depending on location and finish.
- When considering materials for your extension, understand the energy efficiency benefits of modern systems like SIPs and ICF.
- Planning is crucial in any extension project; consult with architects, designers, and contractors to ensure your project meets local building regulations.
- Kitchen extensions, often single-storey, cost from around £50,000 to £120,000 depending on size, complexity, materials, and location.
- Factories prefabricated timber frame extensions have factory quality control, faster on-site assembly, and offer better air-tightness, but have higher upfront costs.
- As you plan your extension project, consider the impact of window and door choices on energy efficiency and overall costs.
- Concrete blockwork extensions have a basic appearance that needs finishing, are weather dependent, and have lower thermal performance compared to newer systems.
- SIPs extensions have excellent thermal performance, quick assembly, and reduced labor costs but have higher material costs and require specialist installation.
- ICF extensions have good thermal performance, quick construction, all-weather building, but are a specialist system, have higher material costs, and require experienced contractors.
- When budgeting for your extension project, don't forget to account for temporary kitchen facilities during construction, garden landscaping costs post-build, and new furniture and appliances.
