Extensions seem straightforward until you’re actually doing one. Then costs explode, timelines double, and you discover problems that could have been avoided with better planning. Most expensive mistakes happen before construction even starts because planning got rushed or skipped entirely. Avoiding common errors saves more money than any other aspect of extensions.
Table of Contents
1. Working With A Building Company Before Finalizing Plans
Drawing plans without professional input creates expensive problems. Builders spot issues that architects and homeowners miss. That beautiful design might be impossible to build as drawn or require structural work, tripling the budget. Getting builder input during planning catches these problems when fixing them is cheap instead of discovering them mid-construction when solutions are expensive.
Collaborating with a building company London prevents the nightmare scenario where construction stops because plans don’t work in reality. Builders see hundreds of projects. They know what works, what fails, and what creates problems. Use that expertise during planning instead of treating builders as just laborers executing someone else’s vision.
2. Understanding Full Costs Before Starting Anything
Your extension budget probably covers construction. Does it cover planning permission fees, building control fees, structural engineer reports, party wall agreements if needed, utility connections or upgrades, temporary kitchen facilities during work, decoration after construction, and landscaping to fix the garden afterwards? Most budgets don’t account for these extras, and they add up fast.
List literally everything involved, including the boring administrative costs nobody thinks about. Budget for all of it. Extensions that start without comprehensive budgets always end with financial surprises that could have been planned for if anyone had bothered thinking through the complete process.
3. Getting Proper Planning Permission Instead Of Assuming Permitted Development
Permitted development rules are complicated and full of exceptions. Assuming your extension qualifies without actually checking with the planning department is gambling with massive stakes. If you guess wrong and build without the required permission, you might be forced to remove what you built. That’s a financial disaster that kills projects completely.
Verify what permissions you actually need before spending anything on construction. Yes, the planning process takes time. Building without proper permission takes even more time when you’re forced to stop work and apply retrospectively, or worse, demolish what you built.
4. Building For Future Needs Not Just Current Ones
Extensions are expensive. Building twice because the first extension became inadequate is even more expensive. Think about future needs beyond just immediate requirements. Growing family? Aging parents who might move in? Work from home space becoming permanent? Build for where you’re heading, not just where you are today.
This might mean slightly larger extension now, costing moderately more upfront, but preventing the need for a second extension later, costing vastly more. Future proofing saves money long term, even though it increases immediate costs slightly.
Conclusion
Extension mistakes get expensive fast. Working with building professionals during planning rather than after, understanding complete costs including boring administrative fees, verifying permission requirements instead of guessing, and building for future needs instead of just current ones prevents the disasters that turn extensions from improvements into financial regrets. Most expensive mistakes happen from poor planning, not from construction itself. Invest time in planning properly and save multiples of that investment by avoiding problems that shouldn’t have happened in the first place.
