Key Takeaway
Understand what extension design fees can include and how to compare written scopes, service levels and project-specific quotes across Hampshire.
How do project costs and planning routes compare?
Extensions add to the building, while loft and garage conversions work with existing space; each has different structural and planning considerations. The route depends on the property, so these comparisons are not an individual planning decision or quotation.
| Project | Typically needs planning? | Main cost factors | Typical design route |
|---|---|---|---|
| Single-storey extension | May qualify for permitted development if all conditions apply | Footprint, foundations and specification | Survey, layout, planning check and technical drawings |
| Two-storey extension | Depends on the design and permitted development limits | Structure, roof design and specification | Survey, planning check and coordinated structural information |
| Loft conversion | Some roof works may qualify, subject to restrictions | Roof type, stairs and structural work | Roof and layout assessment, planning check and Building Regulations |
| Garage conversion | Often possible without a planning application, but exceptions apply | Insulation, structure and services | Survey, planning check and Building Regulations design |
Extension Design Costs in Hampshire: A Guide
This article includes historical 2025 fee examples, not current or verified 2026 prices or a quote. Provider scopes and prices vary; check current package details for Hampshire Build's fees and exclusions. Compare written scopes as well as prices.
Have a project in mind? Start with a few details about your home.
Build an initial project budgetWhat Do Extension Designers Charge in Hampshire?
Extension designers in Hampshire typically charge in one of two ways:
1. Hourly Rates (Traditional Model)
- Junior designers: £60-£80 + VAT per hour
- Experienced designers: £80-£120 + VAT per hour
- Senior/chartered designers: £120-£180 + VAT per hour
- Total project cost: £3,500-£6,400 + VAT+ for typical extension
2. Fixed-Fee Packages (Modern Model)
- Pre-Build Package: £1,950 + VAT (see current page for its stated scope)
- Premium Package: £2,950 + VAT (adds defined contractor tender support and a client-focused building contract issued for signature)
- Premium Plus Package: £3,950 + VAT (adds an indicative staged programme, Building Notice submission and one Party Wall notice to one adjoining owner)
Illustrative Extension Design Cost Categories
The following are examples of services designers may price separately; they are not a statement of Hampshire Build's package inclusions. Confirm scope and current prices with each provider.
Initial Consultation & Site Survey (£300-£800 + VAT)
- Property inspection and measurements
- Site constraints assessment
- Design brief discussion
- Feasibility assessment
Architectural Drawings (£1,200-£2,500 + VAT)
- Existing floor plans and elevations
- Proposed extension plans (all floors)
- Proposed elevations (front, rear, sides)
- Section drawings
- Site location and block plans
Planning Application (£600-£1,200 + VAT)
- Planning application preparation
- Planning portal submission
- Council liaison and query responses
- Design and access statement
Building Regulations Drawings (£800-£1,800 + VAT)
- Detailed construction drawings
- Thermal calculations (U-values)
- Ventilation specifications
- Drainage plans
- Fire safety details
Structural Calculations (£800-£2,000 + VAT)
- Steel beam calculations
- Foundation design
- Load-bearing assessments
- Certification by a qualified structural engineer
Extension Design Costs by Project Type in Hampshire
Single-Storey Extension Design
- Hourly designers: £2,800-£4,500 + VAT
- Fixed-fee packages: £1,950 + VAT
- Average saving: £1,450-£2,550
Two-Storey Extension Design
- Hourly designers: £4,500-£7,000 + VAT
- Fixed-fee packages: £1,950-£2,950 + VAT
- Average saving: £2,550-£4,050
Kitchen Extension Design
- Hourly designers: £3,200-£5,500 + VAT
- Fixed-fee packages: £1,950 + VAT
- Average saving: £1,850-£3,550
Side Return Extension Design
- Hourly designers: £2,500-£4,200 + VAT
- Fixed-fee packages: £1,950 + VAT
- Average saving: £1,150-£2,250
Why Do Extension Design Costs Vary in Hampshire?
- Location: Winchester and Basingstoke command higher rates than smaller towns
- Experience: Senior designers charge 2-3x junior rates
- Project complexity: Conservation areas, listed buildings cost 30-50% more
- Service scope: Full service packages vs basic drawings only
- Billing model: Hourly vs fixed-fee dramatically affects total cost
Hidden Costs to Watch For
When comparing extension designer quotes in Hampshire, beware of these extras:
- Separate hourly fees for routine project communication
- Meeting charges (£80-£150 + VAT per meeting)
- Phone call time (some charge for every call)
- Travel expenses (£50-£150 + VAT)
- Administration fees (£100-£300 + VAT)
- Council application fees (separate - £250-£650 + VAT)
How to Save Money on Extension Design Costs
- Choose fixed-fee packages: Save £2,000-£4,000 vs hourly billing
- Use local designers: Hampshire specialists understand local planning
- Provide clear brief: Reduces back-and-forth
- Bundle services: Planning + building regs together saves money
- Avoid unclear scope: A clear brief helps control costs with hourly designers
Real Hampshire Extension Design Cost Examples
Winchester Kitchen Extension (30m²)
Ready to apply these ideas to your own home?
Check your project costs- Hourly designer quote: £4,200 + VAT
- Hampshire Build Pre-Build Package: £1,950 + VAT
- Saving: £2,250
Basingstoke Two-Storey Extension (45m²)
- Hourly designer quote: £6,800 + VAT
- Hampshire Build Pre-Build Package: £1,950 + VAT
- Saving: £4,850
Southampton Side Return (18m²)
- Hourly designer quote: £3,400 + VAT
- Hampshire Build Pre-Build Package: £1,950 + VAT
- Saving: £2,050
Is Cheaper Extension Design Better Value?
Not always. Consider:
- Planning track record: Experienced designers save money by avoiding rejections
- Well-detailed drawings: Incomplete drawings can lead to contractor queries or additional work
- Local knowledge: Hampshire planning specialists understand council preferences
- Avoid delays: Clear decisions help protect against extended rental costs or delayed moves
Hampshire Build's Fixed-Fee Approach
Our three fixed-fee packages state the fee for their defined scope:
- Pre-Build Package (£1,950 + VAT): Planning drawings, building regulation drawings prepared for Building Notice submission, and required structural calculations prepared by an independent qualified structural engineer
- Premium Package (£2,950 + VAT): Adds tender support to two vetted contractors, cost proposals, a schedule of works and a client-focused building contract issued for signature
- Premium Plus Package (£3,950 + VAT): Adds a staged programme of works, Building Notice submission and one Party Wall notice to one adjoining owner
All packages include an on-site measured survey, planning drawings and building regulation drawings prepared for Building Notice submission, plus required structural calculations prepared by an independent qualified structural engineer. The fixed fee covers the stated package scope; statutory and third-party fees are separate.
What Questions to Ask Extension Designers
- Is your fee fixed or hourly? If hourly, what's the total estimate?
- What exactly is included in your fee?
- How do you set and manage the project scope?
- Can you show recent planning approvals in Hampshire?
- How long will the design process take?
- Are structural calculations included or extra?
- Do you handle building regulations or is that separate?
Total Project Budget: Beyond Design Costs
Extension design is typically 5-8% of total project costs:
- Design fees: £1,950-£6,400 + VAT
- Planning fee: the current published fee (council)
- Building regulations: £400-£800 + VAT (council)
- Construction: £40,000-£100,000 + VAT+ (depending on size/spec)
- Total typical project: £45,000-£110,000 + VAT
Saving £2,000-£4,000 on design fees makes a meaningful difference to your overall budget.
Ready to get accurate pricing for your Hampshire extension? View our fixed-fee packages or book a complimentary consultation to discuss your Winchester, Basingstoke, or Southampton extension project.
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