Planning a Home Extension in London? Here's What You Need to Know First

With property prices in London at an all-time high, more homeowners are choosing to extend their homes rather than move. Whether you're looking to add a rear kitchen extension for a more spacious feel or a loft conversion for extra bedrooms, getting an extension can be a smart, cost-effective way to expand your property and add value.

However, property development in London comes with unique challenges - limited access due to tight spaces, party wall agreements (and disagreements), and strict planning rules in conservation areas can create friction when planning an extension.

Here's what you need to know before getting started:

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Define the Purpose of Your Extension

In a city as condensed as London, every square foot matters. So it's crucial to be clear about what you want from your extension. Are you expanding your kitchen? Adding a home office? Creating a rental studio? Your goals will shape the design, layout, and budget—and help your builder complete the job to your vision. Being as specific as possible at the start will create more ease throughout the rest of the process.

An example of a Regal construction extension

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Set a Realistic Budget (And Include a Buffer)

Prices typically start from around £40,000 for a simple rear extension in London and can easily rise to over £100,000 for larger, high-spec builds. Be sure to include costs for design, planning permission, party wall agreements, finishes, and unforeseen extras—especially if you're working on an older property. We always advise allowing 10-15% extra as a contingency, so as not to be stuck with any hidden costs or last-minute problems.

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Planning Permission and Permitted Development

Many London extensions can fall under Permitted Development Rights, which allow homeowners to carry out work or changes to the property without applying for planning permission. However, this depends on your property type, the size of the extension, and your local borough's rules. If you're in a conservation area, you may face extra planning constraints. It is important to note that flats and maisonettes don't qualify for Permitted Development.

Even if planning permission isn't needed, Building Regulations approval is always required to ensure your extension meets safety and structural standards.

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Be Aware of Party Wall Agreements

In dense areas like London, most terraced or semi-detached properties share walls with neighbours. If your extension work affects a shared wall - for example, digging foundations near it or building against it - you may need to serve notice under the Party Wall Act 1996. This legal process can take a couple of months, so make sure to plan ahead and communicate with your neighbours beforehand to maintain friendly relations.

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Thinking About Extending?

At Regal Construction, we’ve helped London homeowners unlock their properties' full potential with tailored, high-quality extensions. If you’re ready to start planning — or just need honest advice — get in touch for a consultation.