Mark Eden
13 min read
Key Takeaway
Complete breakdown of home extension costs in Hampshire 2025. Detailed pricing for design fees (£1,350-£2,950), construction costs (£1,800-£3,500/m²), planning fees, hidden costs, and real Winchester, Basingstoke, Southampton project examples.
Understanding Extension Costs in Hampshire 2025
One of the first questions Hampshire homeowners ask is 'how much will my extension cost?' The true answer depends on size, specification, location, and hidden costs many don't consider. Here's your comprehensive guide to budgeting for your Winchester, Basingstoke, or Southampton extension project in 2025:
Total Extension Cost Breakdown Hampshire 2025
For a typical 30m² single-storey kitchen extension:
- Design fees: £1,350-£2,950+VAT (3-5% of total project)
- Planning fee: £0-£528 (if planning required, as of April 2025)
- Building regulations: £500-£800 (council fee)
- Construction: £54,000-£105,000 (90-95% of total project)
- Total project: £56,000-£109,000 for 30m² extension
Design and Planning Costs Hampshire 2025
Architectural Design Fees
Hampshire Build Fixed-Fee Packages:
- Essential Package: £1,350+VAT (drawings + planning application)
- Pre-Build Package: £1,950+VAT (complete service - most popular)
- Premium Package: £2,950+VAT (complex projects + ongoing support)
Traditional Hourly-Rate Designers:
- Junior designers: £60-£80/hour (total project: £2,400-£4,800)
- Experienced designers: £80-£120/hour (total project: £3,200-£7,200)
- Senior/chartered designers: £120-£180/hour (total project: £4,800-£10,800)
- Your savings with fixed-fee: £1,050-£8,850
Structural Engineering Costs
- Steel beam calculations: £400-£800
- Foundation design: £400-£800
- Complete structural package: £800-£2,000+VAT
- Included in our Pre-Build Package
Planning Application Fees (as of April 2025)
- Householder planning: £528 (council fee)
- Prior Approval: £240 (for larger Permitted Development extensions)
- Listed building consent: £528 (in addition to planning)
- Conservation area: £528 (same as standard planning)
Building Regulations Fees 2025
Winchester City Council:
- Small extensions (<40m²): £550-£650
- Medium extensions (40-100m²): £650-£800
Basingstoke & Deane Council:
- Single-storey: £500-£700
- Two-storey: £700-£850
Southampton City Council:
- Single-storey: £520-£680
- Two-storey: £680-£850
Construction Costs Hampshire 2025 (per m²)
Single-Storey Extensions
Basic Specification (£1,800-£2,200/m²):
- Standard brick matching existing
- Flat roof with 2 roof lights
- Basic aluminum bi-fold doors (3m)
- IKEA or Howdens kitchen
- Standard porcelain tiles
- No underfloor heating
Good Specification (£2,200-£2,800/m²):
- Quality brick or render finish
- Flat roof with lantern or 4 roof lights
- Mid-range bi-fold doors (4-5m)
- Magnet or Wren kitchen
- Large-format tiles or engineered oak
- Underfloor heating throughout
High Specification (£2,800-£3,500/m²):
- Handmade brick or premium render
- Structural glass roof or large lantern
- Premium slim-frame bi-folds (5-6m)
- Bespoke kitchen (Benchmarx, John Lewis)
- Premium flooring (natural stone, wide oak boards)
- Underfloor heating + smart controls
- High-end lighting design
Two-Storey Extensions
Basic Specification (£1,600-£2,000/m²):
- Matching brick construction
- Standard windows and doors
- Basic kitchen downstairs
- Standard bedroom/bathroom fittings upstairs
- Carpet upstairs, basic tiles downstairs
Good Specification (£2,000-£2,500/m²):
- Quality brick and roof tiles
- Bi-fold doors downstairs
- Good quality kitchen
- En-suite bathroom with quality fittings
- Engineered wood flooring
- Underfloor heating ground floor
High Specification (£2,500-£3,200/m²):
- Premium materials throughout
- Large bi-folds + roof lights
- Bespoke kitchen downstairs
- Luxury en-suite with underfloor heating
- Premium flooring both floors
- Smart heating and lighting
Real Hampshire Extension Cost Examples 2025
Example 1: Winchester Kitchen Extension (30m² Single-Storey)
- Size: 6m x 5m = 30m²
- Spec: Good quality (bi-folds, underfloor heating, Wren kitchen)
- Design fees: £1,950+VAT (Pre-Build Package)
- Planning: £0 (Permitted Development)
- Building regs: £580
- Construction: 30m² x £2,400/m² = £72,000
- Total project: £76,870
Example 2: Basingstoke Side Return (18m² Single-Storey)
- Size: 6m x 3m = 18m²
- Spec: Basic (standard doors, no underfloor heating)
- Design fees: £1,350+VAT (Essential Package)
- Planning: £240 (Prior Approval, as of April 2025)
- Building regs: £520
- Construction: 18m² x £2,000/m² = £36,000
- Total project: £39,590
Example 3: Southampton Two-Storey (40m² Total)
- Size: 5m x 4m each floor = 40m² total
- Spec: Good quality (kitchen downstairs, bedroom + en-suite upstairs)
- Design fees: £1,950+VAT (Pre-Build Package)
- Planning: £528
- Building regs: £720
- Construction: 40m² x £2,200/m² = £88,000
- Total project: £93,268
Example 4: Winchester Conservation Area Orangery (35m²)
- Size: 7m x 5m = 35m²
- Spec: High (brick pillars, glazed lantern, premium kitchen)
- Design fees: £2,950+VAT (Premium Package - conservation area)
- Planning: £528 (conservation area planning)
- Building regs: £650
- Construction: 35m² x £3,200/m² = £112,000
- Total project: £119,398
Hidden Costs Hampshire Homeowners Forget
During Construction
- Temporary kitchen: £500-£1,500 (microwave, mini-fridge, camping stove)
- Eating out: £800-£2,000 (3-4 months no proper kitchen)
- Skip hire: £400-£800 (2-4 skips during build)
- Scaffolding: £800-£1,500 (if not included in builder quote)
- Utilities disconnection/reconnection: £300-£600
- Building Control inspection fees: Included in BC fee
After Construction
- Interior decoration: £1,500-£4,000 (painting, finishing)
- Furnishing: £3,000-£10,000 (dining table, sofas for new space)
- Kitchen appliances: £2,000-£8,000 (if not in builder quote)
- Landscaping reinstatement: £1,500-£5,000 (lawn, paving, fencing)
- Cleaning: £300-£600 (deep clean after builders)
Contingency Costs
- Ground conditions: £1,000-£5,000 (if clay deeper than expected)
- Drainage issues: £500-£3,000 (existing drains need rerouting)
- Structural surprises: £1,000-£4,000 (weak walls, asbestos removal)
- Design changes mid-build: £500-£3,000 (client requests changes)
- Recommended contingency: 15-20% of construction cost
How to Reduce Extension Costs in Hampshire
Design Stage Savings
- Fixed-fee design packages: Save £2,000-£4,000 vs hourly designers
- Permitted Development: Save £528 planning fee + 8 weeks time
- Simple rectangular shape: 15% cheaper than complex shapes
- Standard sizes: Use standard door/window sizes
Construction Savings
- Builder directly: 10-15% cheaper than using main contractor
- Off-season build: November-March often 5-10% cheaper
- Material choices: Aluminum bi-folds vs premium slim-frame saves £2,000-£4,000
- Flat roof: £3,000-£6,000 cheaper than pitched roof for 30m²
- IKEA kitchen: £4,000-£8,000 cheaper than bespoke
What NOT to Skimp On
- Foundations: Hampshire clay needs proper depth
- Insulation: 2025 Part L standards essential
- Bi-fold door quality: Cheap doors fail within 5-10 years
- Underfloor heating: Hard to retrofit later, worth £2,000 investment
- Building regulations: Never skip - expensive to fix later
Extension Costs by Size Hampshire 2025
| Size | Type | Basic Spec | Good Spec | High Spec |
|---|---|---|---|---|
| 20m² | Single-storey | £36,000-£44,000 | £44,000-£56,000 | £56,000-£70,000 |
| 30m² | Single-storey | £54,000-£66,000 | £66,000-£84,000 | £84,000-£105,000 |
| 40m² | Single-storey | £72,000-£88,000 | £88,000-£112,000 | £112,000-£140,000 |
| 40m² | Two-storey | £64,000-£80,000 | £80,000-£100,000 | £100,000-£128,000 |
| 60m² | Two-storey | £96,000-£120,000 | £120,000-£150,000 | £150,000-£192,000 |
Table shows construction costs only - add design fees, planning, building regs, and contingency
Winchester vs Basingstoke vs Southampton: Cost Differences?
Construction costs are remarkably similar across Hampshire in 2025:
- Winchester: £2,200-£2,800/m² average (slightly higher due to affluent area)
- Basingstoke: £2,000-£2,600/m² average (lower due to more competition)
- Southampton: £2,100-£2,700/m² average (similar to Winchester)
- Rural Hampshire: £2,300-£3,000/m² (travel costs, less competition)
Financing Your Hampshire Extension 2025
Payment Options
- Savings: Most cost-effective (no interest)
- Remortgage: 3-6% interest typical (spread cost over 25 years)
- Home improvement loan: 6-12% interest (5-10 year term)
- Personal loan: 8-15% interest (1-7 year term)
Builder Payment Schedule
- Deposit: 10-15% upfront
- Stage payments: 25% at foundations, 25% at roof, 25% at first fix
- Final payment: 15% on completion
- Never pay 100% upfront!
Hampshire Build's Transparent Pricing
Our packages provide certainty on design costs upfront:
- Essential £1,350+VAT: Drawings + planning application
- Pre-Build £1,950+VAT: Complete service (95% choose this)
- Premium £2,950+VAT: Complex projects + ongoing support
All packages include measured survey, architectural drawings, planning application, and council liaison. Pre-Build adds building regulations and structural calculations - everything your builder needs to quote accurately.
Ready to budget accurately for your Hampshire extension? Book a free cost consultation or view our transparent fixed-fee packages serving Winchester, Basingstoke, Southampton, and all Hampshire areas.
More Useful Resources
- Extension cost calculator — get an instant personalised estimate in minutes
- Kitchen extension cost Hampshire 2025 — detailed pricing for kitchen extensions
- House extensions Basingstoke — local cost examples and planning guidance
- Garage conversions Winchester — a cost-effective alternative to extending
- Permitted Development rights guide — when you don't need planning permission
