New Case Study
Mr & Mrs Andrews, St Albans
Read their story →
Extension Design Services
Planning drawings and building regulations for single-storey, double-storey extensions and loft conversions. Serving Hampshire, Surrey, Hertfordshire & surrounding counties. Simple 4-step process, fixed-fee pricing. Use our Extension Cost Calculator for instant estimates.
Choose Your Design Package
Our three comprehensive packages cover everything from planning to on-site build support
- Professional on-site measured survey
- Detailed planning drawings
- Planning application submission
- Full building regulation drawings
- Certified structural calculations
- Everything in Pre-Build Package, plus:
- Detailed schedule of works
- Professional contractor vetting
- Contractor proposal gathering
- Client-focused building contract
Payment Terms
£250 + VAT deposit to begin — balance on completion of design consultation
Simple two-payment structure across all three packages. No milestone payments, no surprises.
Additional storey: £750 + VAT | Loft conversion: £950 + VAT
Calculate Your Extension Cost
Get an instant estimate for your project and receive a personalised proposal
Get Your Free Project Proposal
With real planning data for your area
Select your extension type to continue
Estimates are for guidance only - not a binding quote. Shell/core costs exclude finishes, kitchens, bathrooms, and decoration. All costs exclusive of VAT. See Terms.
Explore More
Professional Services
Essential services to support your extension project. Click to enquire.
Party Wall Notice
Legally compliant party wall notices prepared and served under the Party Wall Act 1996. Required before building near boundaries or shared walls.
Water Board Build Over
Complete build over agreement application with drainage drawings. Required when building over or near public sewers.
Building Control Application
Full application to Building Control or Approved Inspector. Required before construction begins to ensure compliance.
Ecologist Report
Preliminary Ecological Appraisal for planning applications. Required when your site may contain protected species or habitats - common for loft conversions, extensions near trees or hedgerows.
Flood Risk Assessment
Comprehensive Flood Risk Assessment for planning applications. Required when your property is in a flood zone. Includes site analysis, flood zone mapping, mitigation measures and full FRA report for submission.
Your Complimentary Extension Feasibility Assessment
Understanding what's possible before you commit - our comprehensive 30-minute video call consultation covers all the essentials
Cost Feasibility Analysis
Professional cost assessment based on current square metre rates for shell and core builds, giving you realistic budget expectations for your Hampshire extension project.
Physical Space Assessment
Quick professional review to verify adequate land area for your proposed building extension, ensuring your project is physically viable on your property.
Planning History Review
We check publicly available planning history for your property and surrounding area, helping to identify potential opportunities and constraints before we begin the design process.
What You'll Receive
Professional Budget Assessment
Realistic cost estimates based on current market rates and your specific requirements
Site Viability Confirmation
Clear understanding of what's physically possible on your property
Planning Permission Insights
Early identification of planning opportunities and potential constraints
Next Steps Guidance
Clear roadmap for moving forward with your extension project confidently
Ready to Discover Your Extension's Potential?
Book your complimentary 30-minute feasibility assessment and realise what's possible for your Hampshire home
No obligation • Professional advice • Video call consultation
Why Choose Hampshire Build?
With over 15 years of residential design expertise, we deliver exceptional extension design services with transparent fixed-fee pricing and rigorous attention to quality on every project
15+ Years Experience
Over 15 years of residential design expertise with successful projects across Hampshire, Surrey, Hertfordshire, and beyond.
Fixed-Fee Pricing
No hourly surprises. Transparent packages from £1,950 (Pre-Build) to £4,950 (Premium Plus) — you know exactly what you'll pay from day one. Calculate your extension cost
Fast Turnaround Times
Efficient project delivery with streamlined processes that get your extension designs completed quickly without compromising quality.
End-to-End Service
From initial feasibility assessment to building control approval - we handle every aspect of your extension design process.
Our Track Record Speaks for Itself
Successful Extensions
Years of Experience
Planning Success Rate
Complimentary Consultation
Ready to Experience the Hampshire Build Difference?
Join hundreds of satisfied Hampshire homeowners who chose our expert extension design services. Book your complimentary consultation today.
What Our Clients Say
Trusted by Hampshire families for professional extension design services
"Thank you Mark, we have really appreciated how prompt you have been with responding to emails and calls whilst we have been going through design and planning stages. Your reassurance, reliability and professionalism have been a great help."
Sandra Trott
"Excellent service from start to finish. Our original architect continually let us down, but Mark at Hampshire Build was responsive, professional and delivered exactly what we needed for our extension project."
Andrew Stone
"Mark & his team were brilliant in helping us finish off our build - they were kind, efficient and have done a great job. Will definitely be using them again in the future for any work!"
Charlie Brenninkmeijer
Happy with our service? We'd love to hear from you! Your review helps other families find us.
Our Simple, Transparent Process
From initial survey to final technical drawings - we've streamlined the extension design process to deliver professional results quickly and efficiently.
Initial Consultation
Discuss your project requirements and choose your fixed-fee package. Pay £250 + VAT deposit to begin. Simple, low-commitment, and the same for every package.
- Complimentary 30-minute consultation call
- Review property and project requirements
- Explain planning and building regulation requirements
- Choose appropriate package
- Secure your project with deposit
Measured Survey
Professional on-site measured survey within 10 working days of deposit payment. Accurate measurements form the foundation of your design.
- Comprehensive onsite measured survey and property measurement
- Photograph existing conditions
- Identify structural elements and constraints
- Assess planning considerations
- Create accurate base drawings
First Draft Drawings
First draft drawings issued within 15 working days of survey completion. Review and provide feedback.
- Create initial design concepts
- Develop detailed extension design drawings
- Consider planning policy compliance
- Present designs for your review
- Incorporate your feedback and finalise
Finalisation & Submission
Design consultation to finalise drawings, then planning submission and technical documentation as per your package.
- Prepare planning application documents
- Submit to local planning authority
- Create building regulation drawings (Pre-Build)
- Coordinate structural calculations (Pre-Build)
- Provide final technical drawing package
Project Timeline Summary
Typical timeframes for your extension design project
10 Working Days
Measured Survey
On-site survey completed within 10 working days of deposit payment
15 Working Days
First Draft Drawings
Initial design drawings issued within 15 working days of survey completion
Simple Payment Structure
No hidden costs, no hourly rates — just two simple payments from start to finish
Initial Deposit
To secure your project
Paid upon booking to begin the measured survey and design process.
Balance Payment
On completion of design consultation
The balance of your fixed package fee is payable on completion of your design consultation. No milestone payments, no surprise invoices — just two simple payments from start to finish.
Ready to Start Your Project?
Begin your extension journey today with our streamlined process and transparent pricing.