If you’re planning a home extension, cost is usually the first question that needs answering before real planning can begin. This guide sets out realistic price ranges for house extensions across Hampshire, based on current UK build costs and the factors that most affect your final price. Pricing depends on project scope, specification, property type, site access, planning requirements, structural work, and finishes, so treat the figures below as a starting point rather than a fixed quote. See our full range of options on our house extension services in Hampshire page.
Average House Extension Cost in Hampshire
Most fully-finished house extension projects in Hampshire fall somewhere between £1,800 and £2,800 per square metre, including a basic kitchen or bathroom fit-out where relevant. Higher-spec glazing, bespoke joinery, or premium finishes push costs above this range, while a simple shell-only structure can cost less. Two extensions of the same footprint can end up with very different price tags once site access, the condition of the existing property, and finish specification are factored in.
Cost by Extension Type
Single-Storey Extension Cost
A single-storey extension in Hampshire typically costs £35,000-£90,000, depending on size and specification. A modest 20m² addition sits toward the lower end, while a larger 30-40m² extension with bi-fold doors and a vaulted roof costs more.
Double-Storey Extension Cost
Double-storey extensions add significantly more floor space for proportionally less cost per square metre, since foundation and roof costs are shared across two floors. Expect a typical double-storey extension in Hampshire to start from around £60,000, rising with scale and specification.
Kitchen Extension Cost
A kitchen extension usually adds £15,000-£35,000 to the base build cost, covering plumbing, electrics, ventilation, and a new fit-out. Open-plan kitchen-diner extensions are among the most common projects homeowners ask us to quote across Hampshire.
Rear and Side Return Extension Cost
Rear extensions vary widely with size, from around £35,000 for a modest addition to well over £100,000 for a large wrap-around project. Side return extensions, common on Victorian and Edwardian terraces in Southampton and Winchester, tend to cost £20,000-£45,000 depending on width and structural work involved.
What Affects the Price of Your Extension
Several factors influence the final cost of any house extension:
- Size and layout of the new space
- Property type and age, since period properties often need extra remedial work
- Site access, as tight urban plots cost more to build on
- Ground conditions, including Hampshire’s variable clay and chalk subsoils
- Structural work, such as steel beams and load-bearing wall removal
- Roofing, glazing, and door specification
- Electrics, plumbing, and kitchen or bathroom fit-out
- Quality of finishes and fittings
- Planning requirements and any party wall agreements needed
Planning Permission and Building Regulations
Some extensions fall under permitted development rights and don’t need a full planning application, while others do, depending on size, position, and design; requirements vary slightly between local authorities across Hampshire. Every extension must still meet Building Regulations. Budget roughly £200-£1,500 combined for planning and building control fees, plus £1,000 or more if a party wall agreement is needed. We can advise which route applies to your project before any drawings are produced.
Architect, Structural Engineer and Professional Fees
Most projects need input from an architect or architectural designer and a structural engineer, particularly where steel beams or load-bearing walls are involved. Professional fees typically add £3,000-£8,000, depending on complexity and drawing requirements. Where significant structural alterations are involved, it’s worth reviewing our structural works service alongside your plans.
Ways to Control Your Extension Budget
- Agree a clear specification before drawings are finalised, not after
- Get like-for-like quotes so you’re comparing the same scope of work
- Choose finishes early to avoid costly changes mid-project
- Build in a contingency of around 10-15% for unforeseen issues
- Phase optional extras, such as bi-fold doors, if budget is tight
Why Quotes Can Vary Between Contractors
It’s common for quotes on the same extension to differ by tens of thousands of pounds. This usually comes down to what’s included: some builders quote a shell only, others include full electrics, plumbing, and finishes. Always ask exactly what’s covered, and whether the figure is fixed or provisional.
How to Get an Accurate Extension Quote in Hampshire
Because so much depends on your property, site, and specification, the only reliable way to get an accurate cost is a site visit and a proper design conversation. Request a callback and we’ll talk through your project before producing a detailed, itemised quote.
Frequently Asked Questions
Most fully-finished extensions cost between £1,800 and £2,800 per square metre, though this depends heavily on size, specification, and site conditions. A site visit is the only way to get a figure specific to your project.
Not always. Many extensions are covered by permitted development rights, but this depends on size, position, and design, so it’s worth checking before finalising your plans.
A well-designed extension can add meaningfully to your property’s value, though the return depends on your local market, build quality, and how well the new space suits the house.
In most cases, yes. A well-managed build controls access and dust carefully, though kitchen extensions can involve short disruption while services are reconnected.
A single-storey extension typically takes 12-16 weeks to build, while a double-storey extension can take 4-6 months, depending on scale and complexity.
Ready to Plan Your House Extension in Hampshire?
If you’re weighing up your options and want a realistic, no-obligation figure for your project, we’re happy to help. With over 18 years of building experience across Hampshire, we can talk you through what’s achievable for your budget and property. Call Hampshire Building Co. on 01489 358525 or email info@hampshirebuildingco.com to arrange a site visit.
