How much does an extension over a garage cost?

By adding to an existing structure, you’ll be able to make use of otherwise wasted space and avoid eating into your garden. A new pitched roof can often eliminate any water ingress issues that old flat roof garages suffer with, so you can kill two birds with one stone.

Here, we’ll look at the typical cost of an extension over the garage. It can often work out cheaper than building a new extension from scratch, as the groundworks and foundations are already built.

Cost of extension above single garage

An extension over a single garage won’t give you heaps of extra space, but it could still be very useful. For example, you could create a new child’s bedroom or playroom, home office or an ensuite bathroom.

It could cost around £20,000 to build an extension over a single garage, including the roof.

How much would an extension over a double garage cost?

An extension over a double garage gives you lots more space, enough for a new master bedroom or family bathroom.

It can cost around 30% more than an extension over a single garage, and you could pay up to £35,000 for a completed project. Structural issues may complicate matters. If the garage requires underpinning, this can increase the cost considerably. Likewise, if you need to relocate walls or retile for a bathroom where another room was before.

Cost of extension above garage with ensuite bedroom

If you’d like to create a new bedroom with an ensuite bathroom in your new above-garage extension, you’ll find the ensuite to be the most expensive part. Once the extension is built, fitting a bathroom could cost around £5,000.

Extending over a double garage is recommended to give you enough space. But if you only have a single garage, you can still create a new ensuite for an existing bedroom. This means in total, your extension with an ensuite bathroom will cost between £23,500 and £38,000.

One thing worth noting in advance is that garage roof extensions can really highlight how worn out and tired your main house roof is looking. Consider asking your builder for an optional price to re-tile/slate the whole main roof to see if your budget would allow for this work.

FAQs

Can I build an extension over a detached garage?

You can certainly build an extension over a detached garage, this could create an ideal space for a home office or guest room. You might even find it less complicated a project, as the rest of your home won’t be affected by building work. But you need to allow for access, for example, a staircase in the garage into loft space, or otherwise an external staircase. Also, many garages, including detached ones in particular, have inadequate foundations to support an increased amount of brickwork and would need structural surveys and potentially work in the foundations to allow the additional building work to take place.

Will an over-garage extension upset my neighbours?

It’s a good idea to seek advice from your local planning department on how your extension will affect neighbouring properties. There are certain things you may need to do. For example, leaving a gap between your extension and next door’s upstairs avoids what is known as ‘terracing’. You should also avoid blocking your neighbour’s windows or other key fixtures where possible.

You might also want to speak to affected neighbours in advance, to let them know your plans and provide some reassurance.

Do I need planning permission to extend over my garage?

Depending on the size of your extension and other details of your plans, you may not need planning permission. Your extension may fall under what is known as ‘permitted development‘. However, it’s recommended to speak to your local planning department for guidance.