Types of house extensions

Are  you thinking of extending your home, but feel a bit overwhelmed at all the options out there? Our house extensions London and Hertfordshire building specialists have teamed up with an architect to create this article outlining the different types of house extensions to give you an idea of what is involved and how they will transform your home. This guide will help you decide which extension is best for your property.
Types of single storey house extensions

Single Storey Rear, Side and Wrap Around

    Single-storey extensions can help you expand your kitchen or add an extra room to your house. They come in three types. 

  • Rear Home Extensions

  • A popular type of home renovation project, a rear extension takes in the fashion for large open-plan kitchens. You could add sliding glass doors to extend the space out into the garden too.

  • Side Return Extensions

  • A side extension is perfect for owners of older Victorian and Georgian properties with unused side alleyways. It can add up to three metres to the kitchen width, which could transform a small dark room into a bright kitchen-diner. Adding a large roof light or a glazed ceiling will bring extra light into your home. 

  • Wrap Around House Extensions

  • A wrap-around extension (pictured) involves extending both the back and the side of the property maximising the ground floor potential of your home.
 types of double storey house extension

Double Storey Extensions

If you need to add more than one room to your home, a double-storey extension is a cost-effective option as you will be using one roof and the same foundations for both levels.

You could create a large kitchen with dining area and easy access to the garden on the lower half, and an additional bedroom, large family bathroom, office or even a home gym on the second half.

Two storey home extensions can be built onto the back or the side of the house. A rear double-storey extension can have either a flat or a pitched roof, while an extension added onto the side of the house will generally need to have a pitched roof similar to the existing one with the roofline being preferably slightly lower.

Side extension with a basement

Cellar Conversions and Basements


If you have a cellar with a sufficient ceiling height, it is possible to convert it into a living room by simply renovating the interiors, and adding ventilation and lights.

If your property sits on a slope, you could build a semi-basement with a part of the area sitting below the ground. Bringing light and air into half basements is usually straightforward, as you will be able to add windows and in some cases even bi-fold or sliding glass doors.

If you are adding a side or rear house extension to your house, you might be able to incorporate a basement extension into the design, so that you will have a two-storey extension which will only expand one storey above the ground level. This would be beneficial for properties where building a regular double-storey extension is not an option due to design limitations or planning restrictions.

over structure house extensions

Over Structure Extensions

If your house has an attached garage or a previous single-storey extension, you could build a new extension on top of it. In other words, you are 'building over' the existing structure, hence the name.

Some older garages have single-skin brickwork unable to carry the load of another building on top. If this is the case, more structural work would be required to strengthen the original walls before a new extension can be built on top of the garage.

This type of extension project is great if you want to add an extra bedroom, office, study or a playroom for the children.

Loft extension dormer

Loft Conversions

If you have an attic with sufficient floor to ceiling heights, you could create an extra room by simply converting your loft by adding a couple of Velux or other good quality windows to your roof, creating a roof light loft conversion.

If your attic is not high enough, you could still add a room by building a dormer loft conversion or a mansard extension, which will allow you to create maximum head space.

If your property has a hipped roof (a roof that is slopped on three or four sides rather than just two), you might need to extend it by constructing a hip to gable extension first. 


Permitted development rights and planning permissions

Thanks to the recently relaxed Permitted Development rights, most single-storey rear and side extensions, some small two storey rear extensions and Velux and Dormer loft conversions do not require planning permission. Mansard loft conversions, wrap-around house extensions, over-structure extensions and double storey side extensions will usually need permission from your local authority. Below are some of our recently completed projects, explaining which ones required approval and why. If in doubt, you can contact house extension design and build specialists such as Marriott Construction, who are happy to offer professional advice.

One storey rear house extension

One storey rear house extension

One storey rear house extensions qualify under the Permitted Development if they do not extend beyond the back wall of the original house by more than six metres in case of a terraced or semi-detached house or eight metres in case of a detached property. Your extension must not cover more than half of the land surrounding the original building. The roofline must not be higher than four metres. If you live in a flat, maisonette, listed building, or a home located within a conservation area, you will always be required to apply for planning permission.

This single-storey house extension in Barnet, London did not require planning permission as it extends less than six metres beyond the rear wall of a semi-detached house. 

Two storey rear house extension

Two storey rear house extension with semi-basement

A double-storey rear extension might qualify under the Permitted Development providing that it does not expand more than three metres beyond the back wall. The distance between the extension and the garden's rear boundary must be at least seven metres. The addition must not be higher than the original house, and the construction must not include a balcony, veranda, terrace or a raised platform. As with all types of extensions, the appearance of the exterior should match the original house.

This sizeable two-storey extension with a partial basement and a terrace in Hampstead, North West London, required planning permission. 

wrap around house extension

Wrap around house extension

Wrap-around extensions, which use both the back and the side of the house creating an L shape, such as this kitchen extension in Welwyn Garden City, Hertfordshire, always require planning permission from the local authority.

How to Apply?
You can apply for planning permission online at: https://www.planningportal.co.uk/info/200126/applications

If you found this guide useful, visit our Renovation Blog for more House Extension Ideas

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