They’re also transformative when executed well. They add valuable space. They enhance how families live. Getting pricing right from the start ensures you budget appropriately and make informed decisions about your project.
House Extension Cost in London: Price Ranges by Type
Single storey house extensions in London typically cost 1800 to 2500 per square meter construction cost. For a 30-square-meter extension, construction costs range from 54000 to 75000. With professional fees at 10-15% and contingency at 10%, the total project cost likely ranges from 70,000 to 95,000.
Double storey house extensions cost significantly more. Typically, 2800-4500 per square meter. For a 40 square meter extension, total project cost runs 130000 to 200000 or more.
Kitchen extensions typically cost similar to single storey extensions. Pricing depends more on specification than size. Budget kitchens cost less. Premium kitchens cost substantially more.
Loft conversions typically cost 20000 to 50000 depending on conversion type. Simple conversions cost less. Dormer conversions cost more. Mansard conversions cost most.
Wrap around extensions typically cost 2800 to 4200 per square meter. For a 35 square meter extension, total project cost runs 128000 to 190000.
Basement extensions typically cost 1500 to 2500 per square meter but are more complex. Excavation. Waterproofing. Ventilation. Basement conversions are more expensive than ground floor extensions.
These are 2026 prices. Costs have increased since 2025. Material costs remain elevated. Labor costs increased. Building Regulations compliance adds cost.
What Drives House Extension Costs in London
Location within London matters significantly. Central London costs 30 to 40 percent more than outer London. Outer London costs 20 to 30 percent more than the South East regions. Property values and labor costs drive these variations.
Premium materials cost more. Matching existing London brick costs more than standard brick. High-specification finishes cost more than basic finishes.
Planning complexity affects costs. Permitted Development extensions avoid Planning Permission costs entirely. Planning Permission applications incur professional fees ranging from £ 2,000 to £ 6,000. Complex planning situations with multiple revisions cost substantially more.
Conservation Area status affects costs. Extensions in Conservation Areas often face higher design requirements. Better design costs more. Getting approvals sometimes requires design revisions.
Listed building status affects costs dramatically. Listed Building Consent is required for most changes.
House Extension Cost Breakdown: Where Money Goes
Windows and doors range from 3,000 to 10,000, depending on quality and quantity.
Electrical and plumbing cost 4000 to 12000, depending on extent.
Insulation and weatherproofing cost 2000 to 6000.
Internal finishes cost 6000 to 20000, depending on quality.
Kitchen or bathroom installation costs 5000 to 30000, depending on the specification.
Professional fees cost 8000 to 25000, covering architecture, engineering, and Building Control.
A 10 percent contingency covers unexpected issues.
| Cost Component | Budget Range | Mid-Range | Premium | Notes |
| Groundwork | £5-8k | £8-12k | £12-15k | Ground conditions vary |
| Structure | £10-15k | £15-25k | £25-35k | Size and complexity |
| Roof | £4-6k | £6-9k | £9-12k | Design and materials |
| Windows/Doors | £3-5k | £5-7k | £7-10k | Quality varies |
| Electrical | £3-5k | £5-8k | £8-12k | Extent of work |
| Plumbing | £2-4k | £4-6k | £6-8k | Complexity |
| Insulation | £2-3k | £3-4k | £4-6k | Standard levels |
| Finishes | £6-10k | £10-15k | £15-20k | Quality affects cost |
| Kitchen/Bath | £5-12k | £12-20k | £20-30k | Specification |
| Professional Fees | £8-12k | £12-18k | £18-25k | Services included |
| Contingency (10%) | £4-6k | £6-9k | £9-13k | Unexpected issues |
Location-Based Pricing Variations
Understanding your specific location within London helps with budgeting. Central neighborhoods command premium pricing. Outer neighborhoods cost less. These variations are significant.
Professional Fees Impact on Total Cost
Professional fees typically run 10 to 15 percent of the construction cost. For a 70000 construction project, professional fees run 7000 to 10500.
Getting Realistic House Extension Cost Quotes
Getting multiple quotes helps you understand realistic pricing. Different architects price differently. Different contractors price differently. Getting three to five quotes reveals the range.
Don’t just look at total cost. Understand what’s included. What costs extra? What is the timeline is.
Request detailed breakdowns. Understand where costs go.
Extension Architecture: Realistic House Extension Pricing
For your house extension in London, Extension Architecture provides transparent, realistic pricing. Contact them for a consultation and a detailed quote for your specific property.
