Mistakes to Avoid When Planning Your Home Extension in Surrey & London

Planning a home extension in Surrey or London can be an exciting way to unlock your property’s potential and create the space your family needs. But the journey from idea to finished extension is full of pitfalls that can lead to stress, spiraling costs, and disappointing results if not navigated carefully. Here are the top 7 mistakes to avoid, based on years of local experience—and how working with a trusted partner like CAB Design & Build can help you sidestep each one.

1. Inadequate Planning and Rushed Design

One of the most common—and costly—mistakes is jumping into construction without a thorough plan. Detailed design and planning are essential to ensure your extension meets your needs, integrates seamlessly with your existing home, and avoids expensive last-minute changes.

• Start with clear project goals and a comprehensive brief.

• Work with experts to create detailed architectural plans and 3D visuals if needed.

• Factor in flow, natural light, and how the new space will be used for years to come.

2. Underestimating Your Budget

It’s easy to misjudge the true cost of a home extension, especially with fluctuating material and labor prices in Surrey and London. Unplanned extras, delays, and unforeseen issues can quickly blow your budget.

• Obtain a fully itemised quote from your builder—watch out for vague allowances or omissions.

• Allow a contingency fund of 10–15% for unexpected costs.

• Understand what is (and isn’t) included in “the price,” and insist on transparent, fixed pricing.

At CAB Design & Build, what we quote is what you pay—no hidden costs or last-minute surprises.

3. Ignoring Planning Permission and Building Regulations

Assuming your home extension qualifies as “permitted development” is risky. Planning rules can be complex, and every local authority has its quirks, especially in conservation areas or with period homes.

• Always check if you need planning permission and get it secured before starting work.

• Make sure your extension will fully comply with building regulations—including structure, insulation, fire safety, and energy efficiency.

• Neglecting this can mean fines, delays, and even being forced to tear down unlawful work.

Explore our peace of mind guarantee, covering hassle-free permissions and full compliance.

4. Choosing an Inexperienced or Unqualified Builder

The temptation to go with the lowest quote often leads to disappointment—a cheap builder may cut corners or lack the expertise to deliver your vision. Mistakes can be expensive to fix and disrupt your home life.

• Vet your builder’s track record: ask for references, case studies, and proof of insurance.

• Choose a company with local experience, expert project management, and comprehensive deposit protection.

• Beware of vague promises and demand everything in writing.

See how our vetted team delivers quality work backed by real reviews and workmanship warranties.

5. Forgetting About Your Neighbours

A successful extension respects its surroundings. Overlooking your neighbours’ right to light, privacy, or ignoring party wall agreements can land you in disputes—or even project halts.

• Engage with neighbours early in the process.

• Address potential impacts on sunlight, privacy, and access.

• Ensure all necessary party wall notices are served and agreements in place before work begins.

6. Neglecting Practical Considerations Like Infrastructure and Light

Even well-planned extensions can suffer from poor ventilation, insufficient lighting, or impractical layouts if infrastructure and day-to-day usability are overlooked.

• Assess and, if needed, upgrade existing plumbing, electrics, and structural supports.

• Make the most of natural light with strategically placed windows, Veluxes, or glazed doors.

• Ensure smooth flow between new and old spaces; usability is as important as square footage.

Explore our expert home improvement services across kitchen extensions and loft conversions.

7. Overlooking the Future Value and Sustainability

Many homeowners get fixated on today’s needs or cheapest solutions—only to regret not futureproofing their home. Sustainable design features, flexible layouts, and quality materials add real value in the long term.

• Invest in energy efficiency—insulation, quality glazing, and eco-friendly heating.

• Use durable finishes and flexible designs that accommodate future lifestyle changes.

• Think about long-term property value, not just initial cost.

CAB Design & Build advises on every aspect, from material choice to energy-saving upgrades, helping you create a home that’s ready for the future.

Avoid Stress—Build with Confidence

A successful home extension transformation should bring you joy, not headaches. By partnering with local experts who offer end-to-end project management, transparent pricing, and deep local knowledge, you protect your investment and enjoy a smooth journey from concept to completion.

Ready to start planning your home extension in Surrey or London? Book your FREE consultation today and discover why hundreds of homeowners trust CAB Design & Build to turn dreams into reality.

Contact us now or explore our project portfolio for inspiration. Your dream home is just one call away!