How Much Does a House Extension Cost in 2025? (Real Examples from Surrey
Understanding House Extension Costs in 2025
Understanding real costs is crucial if you plan a house extension in 2025. Prices vary depending on the size, design, and finish you choose. Recent shifts in material and labor costs make early planning more critical than ever. This guide shares real project examples from homes across Surrey — including Cobham, Weybridge, and Epsom — to give you a clearer idea of what to expect.
What Is the Average Cost of a House Extension in 2025?
The cost of building a house extension in 2025 primarily depends on the size, design, and specifications of the project.
Here are typical ranges based on real work completed across Surrey:
Single storey extension: £1,800 to £2,400 per square metre (base build)
Double storey extension: Add 40–60% to single storey cost
Kitchen extension (including fit-out): £3,000 to £4,000 per square metre
Rear extension with glazing and skylights: £2,500 to £3,500 per square meter
Loft conversion: £1,500 to £2,500 per square metre
Important:
Higher-end finishes, bespoke glazing, or complex structural work will increase costs.
Site access, ground conditions, and planning requirements can also affect the final figure.
Every home is different, so we recommend starting with a proper conversation rather than relying on online calculators.
5 Key Factors That Affect Extension Costs
Several key factors influence the final cost of a house extension:
Size and complexity of the design
Larger spaces, bespoke layouts, and tricky rooflines all add to the overall build cost.
Type of rooms added.
Due to plumbing, electrics, and fixtures, kitchens and bathrooms are more expensive to fit out than simple living rooms or utility spaces.
Groundwork and drainage needs
Older Surrey homes often require upgraded foundations or drainage adjustments, especially when access is tight or soil conditions are poor.
Quality of finishes
Costs can rise sharply depending on the level of finish, from basic standard fittings to high-end bespoke kitchens, flooring, and glazing.
Planning permission and structural engineering
Some extensions fall under permitted development, but others need full planning permission and structural engineering reports, which add time and fees.
Real Cost Examples From Recent Surrey Projects
Here are real-world examples from recent projects we have completed across Surrey:
Cobham rear kitchen extension – £145,000
A modern rear extension with bifold doors, vaulted ceiling, skylights, and a complete kitchen rework.
(Included structural steelwork, high-end kitchen fit-out, and garden landscaping.)
Weybridge loft and rear extension – £175,000
A combined rear and loft conversion project, adding a new master suite upstairs and an open-plan family living space downstairs.
(Included planning permissions, bespoke glazing, and extensive drainage rework.)
Epsom full-width open-plan extension – £130,000
A full-width ground floor extension, with bifolds onto the garden, skylights, and a large new utility room.
(This included reconfiguring internal walls, installing a new kitchen, and doing external work.)
Each project was tailored carefully to the family’s needs and designed to blend naturally with the existing home.
See What Surrey Families Built
If you would like to see more examples of real project costs, timelines, and stunning finished spaces from homes across Surrey, you can download our 2025 Home Extension Brochure.
Inside, you will find:
5 real Surrey home extensions, fully costed
Actual build timelines and key project details
Honest before-and-after results
What worked, what added the most value, and what to watch out for
Hidden Costs Homeowners Often Miss
When planning a house extension, it is essential to budget appropriately for costs that are not always included in basic quotes:
Planning application fees: Typically £250–£500, depending on your council.
Structural engineer reports: Essential for steelwork design, usually £1,500–£3,000.
Party Wall Agreements: If building near neighbors, budget around £1,000+ for surveyor costs.
Upgraded glazing and bespoke kitchens: High-end choices can add significantly to the overall spend.
Landscaping and garden restoration: Often needed after construction work disrupts outdoor spaces.
Planning for these early avoids nasty surprises once the building is underway.
Is It Worth Extending in 2025?
For most Surrey homeowners, extending remains one of the smartest ways to add value and improve daily living.
Well-designed extensions typically add 10–20% to a property's value.
Extending avoids stamp duty, moving costs, and the hassle of relocating.
You stay in the home and area you love, with space properly tailored to your life.
The key is planning carefully, setting realistic budgets, and choosing a team that can deliver properly.
Next Steps: Planning Your Project Properly
The best time to start planning is before you get stuck comparing quotes with no clear plan.
A short conversation now could save months of second-guessing later.
You will get a clearer idea of realistic costs, timescales, and options based on real experience.
Ready to Plan Your Project Properly?
If you are serious about extending your home in 2025, the best first step is getting real advice based on your space, your goals, and your budget.
In a short planning call, we can help you:
Understand realistic costs for your project
Spot potential planning or design challenges early
Map out a clear timeline from start to finish
Answer any questions before you commit to anything
It is a proper conversation — no pressure, no obligation, just the right advice at the right time.