If you love your current neighborhood in Southampton but your family is outgrowing your living space, building an extension is often a much smarter choice than dealing with the massive fees, stamp duty, and hassle of moving house.
However, before you start looking at architectural designs, the number one question on every homeowner’s mind is: How much is a home extension actually going to cost?
Because construction costs depend heavily on the type of build, materials, and specific local conditions, there isn’t a single “one-size-fits-all” price. In this guide, we break down the current average extension costs across Southampton and Hampshire to help you budget effectively for your next project.
Average Cost per Square Metre (m^2)
In 2026, the baseline cost for a standard, straightforward home extension in the Southampton area generally falls between £1,750 and £3,000+ per square metre.
Basic Build Quality: £1,750 – £2,200 per m^2 (Standard materials, basic layouts, plastered walls)
Premium/Complex Build Quality: £2,500 – £3,500+ per m^2 (Premium finishes, large structural steel openings, complex glazing, or bi-fold doors)
Breaking Down the Costs by Extension Type
To give you a better idea of a total project budget, here is what you can typically expect to look at based on the style of extension you want to build:
1. Single-Story Rear or Side Extension
Perfect for creating those open-plan kitchen and dining spaces that completely change how a family lives.
Average Total Cost: £35,000 – £75,000+ (depending entirely on length, width, and glazing options).
2. Two-Story Extension
If you need both a larger living room and an extra bedroom upstairs, a two-story build offers the best value for money per square metre because you are utilizing the same foundation and roof structure.
Average Total Cost: £70,000 – £120,000+.
3. Wrap-Around Extension
Combining a side and a rear extension into an ‘L’ shape completely transforms a property, but it requires substantial structural engineering and support beams.
Average Total Cost: £65,000 – £105,000+.
What Hidden Factors Push Up the Final Bill?
When plotting out your construction budget, make sure you account for these crucial variables that sit outside the raw building costs:
Ground Conditions & Excavations: Ground layout is everything. If your garden has a significant slope, requires deep trench excavations due to soft soil, or sits near large tree roots, the groundwork and foundations will require more labor, safety checks, and concrete.
Structural Steelwork: If your dream is to completely knock out the back wall of your house for massive, seamless bi-fold doors, the price of structural steel beams will increase your budget.
Kitchens and Bathrooms: If your new extension includes a new kitchen fit-out or a utility room plumbing setup, you must factor in the cost of those premium appliances and tiling on top of the standard structural build.
Professional Fees: Don’t forget to budget roughly 10% to 15% extra for your architect drawings, structural engineer calculations, local council Building Control inspection fees, and party wall agreements if you share a boundary.
Ready to Discuss Your Project?
At Solent Pro Builders, we pride ourselves on delivering trusted, premium-quality renovations and structural builds across Southampton. We work directly with you to ensure your project stays structurally sound, entirely compliant with local council inspectors, and finished to the highest