The Top 5 Mistakes Homeowners Make When Planning an Extension

Planning a home extension is exciting — but it’s also easy to make avoidable mistakes that slow things down or cost more in the long run. At Plan My Extension, we’ve worked with plenty of homeowners who’ve been through it before, and we know what trips people up.

Here are the top five mistakes to avoid when planning your extension — and how our approach helps you stay one step ahead.

One of the biggest missteps is starting a project without being sure whether planning permission is required. Some extensions fall under Permitted Development, but many don’t — especially in conservation areas or if you’re building close to boundaries.

How PME helps: We’ll assess your project early and let you know if a planning application is needed. If it is, we prepare and submit it for you.

Without accurate measurements, nothing else can happen — yet many projects stall because a survey hasn’t been booked or completed. The longer you wait, the more things get pushed back.

How PME helps: Our survey process is fast, simple, and remote — either self-led or done by one of our trusted builders. No waiting for site visits or long lead times.

Even if you don’t need planning permission, most extensions still need building control approval. Forgetting this can lead to work being delayed or even stopped once it starts.

How PME helps: Our Technical Package includes all the drawings your builder needs to pass building control and start work without hold-ups.

Choosing a builder based on price alone — without checking experience or communication — can lead to delays, extra costs, or poor workmanship.

How PME helps: We connect you with vetted, PME-approved builders who understand our plans and know how to deliver them on site.

Many homeowners dive into building work without a clear set of drawings or scope. This can lead to miscommunication, changing costs, and last-minute decisions that create stress.

How PME helps: Our fixed-fee packages give you a clear, complete plan from the outset — so you know what’s happening, when, and why.

Most extension mistakes come from unclear steps, bad timing, or the wrong people. With Plan My Extension, you get straightforward, affordable support that helps you avoid the common pitfalls — and get your project moving smoothly.