8 Common mistakes to avoid when extending your home
Extending your home is an exciting opportunity to create more space, improve functionality, and add long-term value to your property. However, it’s also a major undertaking that comes with its fair share of pitfalls. At Project Nine, we’ve guided numerous clients through successful extensions - from contemporary open-plan kitchen additions to characterful period renovations. Drawing from that experience, here are eight common mistakes to avoid when planning your home extension.
1. Underestimating the True Cost
A frequent error is budgeting only for the build itself. The reality is that costs extend beyond construction - think planning fees, architectural design, structural engineers, party wall surveyors, project management, and VAT. A realistic budget should include a contingency fund of around 10–15% to account for unforeseen issues.
Project Nine Tip: We offer transparent budgeting from the outset, including professional fees and finishes, so there are no surprises down the line.
2. Skipping the Design Phase
Rushing straight into the build without properly considering the layout, proportions, or natural light can lead to disappointing results. A well-designed extension should feel like a seamless continuation of your home, not an afterthought.
Project Nine Tip: Our design-led approach ensures that every extension complements your existing space - both aesthetically and functionally.
“From our initial encounter… their professionalism was evident… we are delighted with the quality of the work and are thoroughly enjoying our newly renovated home.”
3. Overlooking Planning Restrictions
Whether it’s permitted development, conservation area rules, or listed building consent, failing to research planning requirements can cause costly delays. Even if your extension falls under permitted development, prior approval may still be needed.
Project Nine Tip: We can help advise how to handle the entire planning process working alongside the architect to ensure the process is as smooth as possible.
4. Ignoring the Neighbours
Neighbours can have a powerful influence on planning permission - especially if you share a boundary. Poor communication can result in objections or party wall disputes, which could delay your build.
Project Nine Tip: We recommend involving your neighbours early. A courtesy conversation goes a long way in keeping the project smooth and amicable.
5. Choosing Style Over Function
A visually striking extension that doesn’t work with your lifestyle or flow of the house can be frustrating in the long term. For example, an ultra-modern glazed box might not retain heat well or provide adequate privacy.
Project Nine Tip: We prioritise balance - beautiful design that supports how you live in the space every day.
6. Neglecting the Existing Layout
An extension should enhance your home, not just add square footage. That means considering how the new space connects to existing rooms and rethinking the internal flow.
Project Nine Tip: We look at your home holistically - sometimes reconfiguring existing rooms can unlock more potential than simply adding more space.
7. Assuming You Can Live Through the Build
Major construction work is disruptive, messy, and loud. While it’s tempting to stay put and save on temporary accommodation, living onsite can slow the project down or increase stress.
Project Nine Tip: We’ll advise early on whether temporary relocation is necessary and help plan timelines to minimise disruption.
8. Hiring on Price Alone
Going with the cheapest quote often leads to cost-cutting on materials, poor communication, or lack of accountability. The long-term cost of fixing mistakes can outweigh the initial saving.
Project Nine Tip: Our vetted build partners share our commitment to quality, and our team remains involved from start to finish to ensure your investment is protected.