Planning a home extension is one of the most exciting yet daunting projects a homeowner can undertake. Whether you're looking to add a kitchen extension, create additional bedrooms, or build a stunning open-plan living space, proper planning is essential for success. With over 20 years of experience building extensions across Kent, we've guided hundreds of homeowners through this process. Here's everything you need to know.
Understanding Your Needs and Budget
Before contacting builders or architects, spend time understanding exactly what you need from your extension. Are you addressing a specific problem (lack of space, dark rooms, poor layout) or pursuing an aspiration (luxury kitchen, home office, guest suite)? Document your requirements clearly:
- Space requirements: How many additional square metres do you need?
- Functionality: What will the space be used for?
- Design preferences: Contemporary or traditional? Lots of glass or solid walls?
- Budget: Realistic budget including 10-15% contingency
- Timeline: When do you need the work completed?
Extension costs in Kent typically range from £1,500-£2,500 per square metre depending on specification. A 25 square metre single-storey extension would cost £37,500-£62,500. Higher specifications with bifold doors, underfloor heating, and premium finishes increase costs towards £3,000 per square metre.
Do You Need Planning Permission?
Many extensions can be built under Permitted Development Rights without planning permission, but there are specific criteria:
Permitted Development allows:
- Single-storey rear extensions up to 6 metres (detached houses) or 4 metres (semi-detached/terraced)
- Two-storey rear extensions up to 3 metres beyond the original house
- Extensions no higher than 4 metres (single-storey with pitched roof)
- Side extensions up to 4 metres high and 2.5 metres wide
You'll need planning permission if:
- Your extension exceeds permitted development limits
- Your property is listed or in a conservation area
- You want to extend the front of your house
- Previous extensions have used up permitted development rights
We recommend a pre-application consultation with your local planning authority (Tonbridge & Malling, Sevenoaks, Tunbridge Wells, etc.). This costs around £150-£300 and provides valuable feedback before formal submission.
Choosing the Right Design
Good extension design seamlessly integrates with your existing property whilst maximising functionality. Consider:
Orientation and Natural Light: South-facing extensions receive excellent natural light throughout the day. North-facing extensions may need larger windows or skylights.
Proportions: Extensions should complement your existing property, not overwhelm it. A small house with a massive extension looks unbalanced.
Materials: Match or complement existing materials. For period properties, using reclaimed bricks maintains character. Modern extensions often benefit from contrasting materials that acknowledge the old whilst embracing the new.
Internal Layout: Think beyond the extension itself – how will it connect to existing rooms? Will you remove walls to create open-plan living? Where will services (heating, electrics, plumbing) run?
Many clients work with architects to develop designs, but experienced builders like ourselves can also advise on design development, drawing on extensive practical experience.
Building Regulations Compliance
All extensions must comply with Building Regulations, covering structural integrity, fire safety, ventilation, energy efficiency, and sound insulation. Your builder handles Building Control liaison, ensuring:
- Foundations: Adequate depth for ground conditions (typically 1-2.5m in Kent)
- Structural elements: Properly sized steelwork, lintels, and wall ties
- Insulation: Meeting current U-value requirements for walls, roof, and floors
- Drainage: Compliant foul and surface water connections
- Electrics: Safe installation by qualified electrician
Building Control inspects at key stages (foundations, drainage, structural elements, completion) and issues a completion certificate confirming compliance.
Selecting Your Builder
Choosing the right builder is crucial. Look for:
- Local reputation: Check reviews, ask for references, view completed projects
- Experience: Proven track record with similar extensions
- Insurance: Public liability and employer's liability insurance
- Detailed quotations: Clear breakdown of costs, not just a total figure
- Transparent communication: Responsive, clear explanations, regular updates
Beware of unusually low quotes – they often indicate corners being cut or hidden costs emerging later. The cheapest quote rarely delivers the best value.
The Build Process Timeline
Typical single-storey extension timeline:
Weeks 1-2: Groundworks (excavation, foundations, drainage) Weeks 3-5: Brickwork to wallplate Week 6: Roofing and windows/doors Weeks 7-8: First fix (electrics, plumbing, insulation) Weeks 9-10: Plastering Weeks 11-12: Second fix (kitchen, bathroom, decorating)
Two-storey extensions take 16-20 weeks. Weather, material availability, and complexity affect timelines.
Living Through the Build
Most homeowners remain in their homes during extension work. We create clear separation between construction and living areas, using dust barriers and temporary external access where possible. For kitchen extensions, temporary kitchen facilities (small cooker, sink in utility room) maintain functionality.
Final Thoughts
A well-planned, well-executed extension transforms your home and adds significant value. Take time in the planning stage, choose your builder carefully, and maintain clear communication throughout. The result – a beautiful extension that feels like it was always part of your home.
Ready to start planning your extension? Contact Carey Brothers & Sons for a free consultation and no-obligation quote. With over 20 years of experience across Kent, we'll guide you through every step from initial ideas to final completion.
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