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Flat roof single storey extension: everything you need to know

5 min read
Oct '25 • by Heather

Quick summary

A flat roof single storey extension typically costs around £1,850 per square metre, with an average total of about £52,500 for a standard project, including VAT. This price depends on size, materials, and features, but smaller or simpler extensions tend to be cheaper. Most are quick to build, but costs can vary based on specific requirements.

As time flies, your family’s needs change, and you might find that you need more space in your home. Instead of moving to satisfy that need, you should consider installing a single storey extension instead.

One major factor to consider when installing an extension is the roof type — flat or pitch roof single storey extension? Whichever you decide on will significantly affect the functionality of your extension and its overall look.

While pitched roofs have a traditional look and blend in easily with older, historical houses, flat roof extensions have a more modern appeal and afford you more flexibility to play around with non-traditional designs.

In this post, we’ll be covering everything you need to know about installing a flat roof single storey extension. From types of flat roof extensions to their cost, requirements and regulations for installation, and, of course, some examples of past projects to get you thinking.

Why install a flat roof single storey extension?

Although flat roofs are famous for developing complications like gathering water and requiring frequent maintenance (complications easily tackled by proper construction), they’ve their fair share of benefits. Here are some reasons you should consider installing a flat roof single storey extension:

Extra space

Installing a flat roof single storey extension allows you to add that extra living area you’ve been craving. They’re an excellent solution for growing families and will help you avoid the hassle of uprooting your family and moving house. As a bonus, also get the option of converting your flat roof to a terrace or garden.

Cost

Installing a flat roof single storey extension generally requires fewer materials, labour, and time than a pitched roof. Hence, flat roof single storey extensions are generally cheaper to install than their counterpart.

How much does an architect charge?