Key Takeaway
Wondering what a house extension costs in Hampshire in 2026? We break down real prices by extension type, size and finish — with no hidden surprises.
If you're a homeowner in Hampshire thinking about extending your property, the first question you'll have is: how much is this going to cost?
It's the right question — and the honest answer is that costs vary depending on the type of extension, the size, your location in Hampshire, and the finish you're after. In this guide, we'll walk you through realistic price ranges based on what we're seeing on real projects across Hampshire in 2026.
Average Extension Costs in Hampshire (2026)
As a general starting point, most homeowners in Hampshire can expect to pay somewhere in the range of £1,800 to £2,800 per square metre for a quality home extension, depending on specification.
Here's how that breaks down by common extension types:
Single-storey rear extension
The most common type. For a standard 20–30m² rear extension in Hampshire, expect to budget £45,000 to £75,000 fully finished. This includes structural work, insulation, glazing, and a plastered, painted finish ready for your kitchen or living space.
Double-storey extension
More cost-effective per square metre than a single storey because you share foundations and roof costs across more floor area. A typical double-storey addition runs £80,000 to £140,000 depending on size and specification.
Side return extension
Popular in Hampshire's Victorian and Edwardian terraces, particularly around Southampton and Portsmouth. These narrower additions can transform a kitchen. Typical costs range from £35,000 to £65,000.
Wrap-around extension
Combines rear and side return into one larger L-shaped space. Costs typically start at £70,000 and can reach £120,000+ for larger projects with high-end glazing and finishes.
Loft conversion
Not technically a ground-floor extension, but often considered alongside them. A full dormer loft conversion in Hampshire typically costs £45,000 to £80,000 and adds a bedroom and bathroom without touching the garden.
What Affects the Cost of an Extension in Hampshire?
Beyond type and size, several factors move the price up or down:
- Specification and finishes. A standard finish — plastered walls, basic glazing, concrete floor — sits at the lower end of the range. Add bi-fold doors, underfloor heating, structural steel, or a flat roof with a roof lantern, and costs climb accordingly.
- Ground conditions. Hampshire has varied soil conditions. If your home sits on clay soil (common across much of the county) or near chalk, additional foundation work may be needed. A site survey before finalising a budget is always advisable.
- Existing structure. Older properties, particularly those built pre-1970, often need additional structural work to tie a new extension into the existing building safely.
- Planning and Building Control. Most rear extensions up to 8 metres on a detached home (6 metres on a semi or terrace) fall under Permitted Development or Prior Approval, avoiding a full planning application — but Building Control sign-off is still required on all extensions. We handle both for our clients as part of our fixed-fee design packages.
- Location within Hampshire. Labour and material costs can vary slightly across the county. Projects in and around Winchester, Basingstoke, and Andover tend to sit in a similar range to Southampton and Portsmouth, though access and site constraints can make a difference.
Design Fees: Fixed-Fee Packages vs. Hourly Rates
One of the biggest concerns homeowners have — and rightly so — is cost uncertainty. Many designers charge by the hour, making it difficult to know what you'll pay before work begins.
At Hampshire Build, we operate on a fixed-fee design package model, meaning the design fee you're given at the start is the fee you pay. No hourly billing, no surprise additional charges. Our fixed-fee design packages cover everything from feasibility report and measured survey through to planning drawings and application submission, with building regulations drawings and structural coordination available in higher-tier packages.
Our packages start from £1,350 + VAT for the Essential Package, rising to £1,950 + VAT (Pre-Build) and £2,950 + VAT (Premium). Each package has its own milestone payment schedule — you only pay the next stage when we deliver it. View full details on our Design Packages page.
What Hampshire Build's Design Service Covers
When you work with us, your fixed-fee design package includes:
- Comprehensive feasibility report
- Professional on-site measured survey
- Expert design consultation
- Detailed planning drawings
- Complete planning application submission
- Building regulation drawings (Pre-Build and Premium packages)
- Certified structural calculations (Pre-Build and Premium packages)
- Schedule of works, contractor vetting and building contract (Premium package)
Our design fee is separate from construction costs, planning authority fees, Building Control fees, and any specialist reports. This separation is intentional: it means you receive fully costed, professionally drawn plans before committing to a builder, giving you the information you need to get competitive build quotes and control your total budget.
How to Get an Accurate Cost Estimate
The best way to understand what your specific extension will cost is to use our extension cost calculator — it gives you a realistic estimate based on your extension type, size and finish level in under two minutes.
From there, you can book a complimentary 30-minute consultation with Mark to discuss your project, understand your options, and get a clear fixed-fee design price with no obligation.
Frequently Asked Questions
Do I need planning permission for an extension in Hampshire?
Most single-storey rear extensions fall under Permitted Development rights, meaning no formal planning application is needed. However, extensions over 4 metres depth on a detached home (3 metres on a semi or terrace) without Prior Approval, two-storey extensions, side extensions, and any work on properties in conservation areas will need formal planning permission. We advise on the planning position for your specific property as part of every complimentary consultation.
How long does an extension take to build in Hampshire?
A typical single-storey extension takes 10–16 weeks from groundworks to completion. Double-storey or more complex projects can take 20–28 weeks. Your builder should provide a clear construction programme before work begins. Hampshire Build's design phase — from deposit to planning drawings — typically runs 6–10 weeks.
Can Hampshire Build help with the design as well as finding a builder?
Yes. Our Premium Package includes contractor vetting, proposal gathering from two vetted building teams, and a client-focused building contract — providing comprehensive support from initial design all the way through to the start of construction. Our Essential and Pre-Build packages focus on the design and planning or building regulations drawings respectively.
Are Hampshire Build's prices fixed?
Yes. All three of our design packages are fixed-fee. The price quoted at the start is the price you pay. Each package has its own milestone payment schedule, and you only pay the next stage when we issue that stage of work to you.