What is a home extension?

A home extension is an additional area built onto your existing property. This can be to the front, side, rear, height or any combination of those.

For example, a wraparound extension builds outwards to the back of your property as well as down one or both side returns. A garage extension typically builds to the side of the frontage of your home, and a rear extension builds out into your garden space.

Which type of extension you choose depends on:

  • What you will use the additional space for
  • How much budget you have to allocate to the project
  • Where around your property you have land to build on

What are the fastest extensions to build?

Since there are so many choices when it comes to building an extension, it is important to understand how long the process might take. A simple extension without any extensive interior works and that comes prefabricated can be erected in as little as a week.

Larger extension projects requiring new foundations to be dug, external walls, roofing and windows to be installed and complex structural work can take six months and upwards.


How much does an extension cost?

The simplest way to think about an extension cost is in terms of square meterage. Costs in London and the southeast tend to be higher than elsewhere in the UK.

A typical extension cost is from £1,500-£2,000 per m2. In London, this can rise to £2,000-£2,500 per m2. If you are considering a build of around 5 metres square you can, therefore, expect to budget around £32,000-£50,000 in total.

It is worth considering whether any planning permissions, Party Wall Agreements or other certifications will be required, in which case those costs need to be added to the budget. The design and approvals process for a complex build can take several months in itself and may increase the total timescale to around one year.

What factors impact the cost of an extension?

There are lots of factors to consider; these include:

  • What the intended use of your extension is; if you are extending a kitchen or building a new bathroom then there will be costs involved to purchase new units and worktops, as well as the interior installation work.
  • How much glazing is involved in your extension? Triple glazing is the most energy-efficient option, and can cost around £300 per window, but will be more expensive for bespoke sized windows or over-size frames.
  • How easy your site is to access. For properties in built-up urban areas site access can be a challenge and specialist equipment might be needed to transport materials, dig foundations and support your build during the construction.
  • Whether you plan to complete any of the work yourself. Some homeowners opt to purchase a shell extension, whereby only the external build is completed and they can either hire independent tradespeople for the rest of the work or complete this themselves.
  • What sort of materials you require. Popular materials such as brick, uPVC and laminate floorings can be relatively low cost. Bespoke materials such as polished concrete or oak timber frames are much more expensive.

What are the benefits of building an extension?

There are lots of reasons to build an extension to your home. Some include:

  1. Increased living space
  2. Improved property value
  3. Making use of empty parts of the property
  4. Upgrading your home
  5. Expanding rooms such as kitchens and living areas
  6. Building a new room, such as a home office or playroom
  7. Creating capacity for a growing family
  8. Generating extra storage space to de-clutter your home

Frequently Asked Questions

Do I need planning permission for an extension?

Whether or not you need planning permission depends on the size of your build, the materials you use, whether you are in a conservation area, and how the extension relates to the size of your existing property.

Most extensions within the below criteria are eligible for permitted development, and therefore do not require planning permission. However, it is best to check with your local planning authority before beginning any work to ensure that you are compliant with their rules.

  • The extension does not accommodate more than half of the land available around the original property. Please note that this includes any previous extensions.
  • The extension is not adjacent to a public road at the front or side.
  • The highest point of the extension is not higher than the existing roof peak.
  • For a single-story extension on a semi-detached or terraced property, the rear of the build does not extend past the original property by more than 3 metres. This extends to 4 metres for detached homes.
  • The extension is no higher than four metres, for a single-story extension.
  • The extension uses materials of a similar appearance to the existing property.

Please note that these are just some of the exceptions and that others may apply.

What types of extension design can I choose from?

There are lots of options when choosing your extension design. Some of the most popular include:

  • Side return extensions alongside the side of your home
  • Rear extensions building outwards into your garden
  • Sunroom or conservatory extensions
  • Timber frame extensions
  • Wrap-around extensions at the rear and side of your property
  • Garage extensions
  • Two-storey extensions to create extra living space
  • Dormer extensions to convert your attic or upper floor space
  • Porch extensions to the front of your property
  • Shell only extensions

Remember that whichever type of extension you choose, Building Regulations may apply. This process is provided by your local authority who will send a Building Control inspector at intervals throughout your build to ensure that safety standards are met.

Mike Alexander
Hey there, I'm Mike - writer and part time home improvement expert at Refurbb. Since owning and refurbishing my own property in 2018, I've since been developing rental properties, writing about my home improvement endeavours, sharing what I've learned and connecting readers to reputable tradespeople in the UK.

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