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Flat Roof Single Storey Extension

Flat roof single storey extension: everything you need to know

By Heather · 07 Mar '22  · 

4 min read


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.


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.

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Two Storey

Gives you glazing freedom

One of the biggest perks of a flat roof is the glazing freedom it allows you. A flat roof will enable you to install more glazing than a pitched roof would.


There’s almost no limit to what you can do with the extra space from a flat roof single storey extension. You could turn it into a gym, study, bedroom, or use it for storage. Also, their structure allows you more freedom to experiment with non-traditional layouts and floor plans.

Types of flat roof extension

Solid roof single storey extension

Solid roof extensions are entirely covered so that there are no transparent elements. They’re characterised by several layers of insulation, making them more energy-efficient than other types of flat roofs. You also enjoy complete privacy from above and improved acoustics with solid flat roofs.

Glass roof flat roof extension

Glass roofs usually feature a large portion of glazing. They are very modern in style and are perfect for maximizing the light coming into your single storey extension for a visually stunning effect. The entrance of natural light will open up your living area and make the room appear bigger and more spacious.

Lantern roof

A lantern roof typically has skylights or roof lanterns attached to it. This is an excellent way of letting in natural light and adding height to your room. Although slightly costlier than solid flat roofs, lantern roofs create a striking effect, really adding a feature to your home.

Get inspired: a solid flat roof extension in Runnymede

Flat roof single storey extension in Runnymede, completed 2020

A flat roof single storey extension in Runnymede, completed 2020

A flat roof single storey extension in Runnymede, completed in 2020

By knocking through an existing wall between the kitchen and living room, these homeowners were able to get twice the amount of space out of their flat roof single storey extension. To help keep lots of natural light flooding in, they paired skylights with a beautiful set of bifold doors.

How much will installing a flat roof single storey extension cost?

Adding a flat roof extension to your home could be pretty expensive regardless of how small or simple it is. Still, its cost is well worth it as a flat roof extension increases your living space and, when done right, adds to the value of your home.

On average, a flat roof extension could cost about £52,500, which comes to around £1,850 per m2. Still, these figures are pretty vague and will be affected by factors such as the extensions’ size, materials, added features, and the condition of your current space.

If you’d like a more specific evaluation of how much it would cost to install your flat roof single storey extension, you can talk about your project to a Resi expert or use our cost calculator here.

Regulations and requirements for installing a flat roof single storey extension

For your extension to be deemed habitable, it must meet building regulations. Building regulations are standards concerning insulation, drainage, and ventilation that have been set in place to ensure that buildings are safe and fit to be occupied.

Here are some of the building regulations flat roof single storey extensions must follow:

  • The flat roof must have a slope of 1:8
  • Water should drain to one or two edges
  • Cold roofs must have ventilation
  • Roofs must be wind resistant and strong enough to walk on
  • Warm roofs must have a VCL bonded to the deck

The guidelines stated above are a few of the many building regulations associated with installing a flat roof single storey extension. We recommend you discuss your project with one of our experts to ensure that your project is compliant.

In many cases, you won’t need full planning permission to install a flat roof single storey extension since single storey extensions fall under permitted development rights. However, there are exceptions to this. If you’re living in a flat, maisonette, or a listed building, you’ll most likely need to apply for planning permission as permitted development rights typically do not apply there.

Also, if your home is located in a conservation area, there might be limitations to permitted development rights. Hence, we recommend you consult your local authority on this.

Resi offers an all-in-one platform that can help ease the burden of bringing your dream flat roof single storey extension to life. From planning permission to building regulations, hiring contractors, and picking the best materials, our consultation team is here to help — we even offer financing solutions!

Ready to get started? Get a free Resi quote here. You can also contact us for more information on the financing solutions we offer.

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