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Last updated on April 3rd, 2023

Bedroom extension cost guide

Dreaming of a spacious master bedroom, or need an extra child's bedroom? With a bedroom extension, you can create lots of extra living space. It can help you turn a tiny box room into a decent-sized child's bedroom, or add an ensuite bathroom to an existing bedroom.
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In this guide, we’ll look at the average bedroom extension cost. Unless your home is a bungalow or has bedrooms on the ground floor, you’ll probably need to build a two-storey extension. This will undoubtedly cost more, but it creates more space downstairs too.

Master bedroom extension cost

The cost of extending your master bedroom depends on a few factors. There are build costs to pay, plus planning application and building regulation fees. You may also need to pay professional fees if you employ an architect or structural engineer to work on your project.

It can also be more expensive to have building work done depending on where you live (i.e. London).

 Low costHigh costAverage cost
Single storey extension £16,000£67,000£41,500
Two-storey extension £24,000£100,500£62,250
Adding ensuite bathroom £3,000£10,000£6,500

Our costs are ballpark averages – get a local tradesperson to quote now

Lastly, the size of your planned extension will inevitably affect the cost. Costs for a small (3m x 5m) single-storey bedroom extension start from around £16,000. This could shoot up to as much as £67,000 for a large (6m x 8m) extension on one floor.

If your bedrooms are upstairs, you may need to build a two-storey extension in order to create more space. This is likely to cost around 50% more than building a single-storey extension. This can push the total price up to between £24,000 and £100,500. This isn’t a set-in-stone rule though. There are also additional costs for things like structural support and changing the roof to factor in.

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Adding ensuite to bedroom cost

Bathrooms tend to cost more to build and fit than bedrooms. If you plan to add an ensuite, you could expect to pay between £3,000 and £10,000 on top of the basic extension build costs.

Luxury en suite

Fittings and finishings

With the shell of your extension complete, it’s time to finish it. If you plan to keep the finish simple with paint and relatively cheap flooring such as carpet, you won’t pay much at all.

But if you have grander plans for bespoke joinery and high-spec flooring, make sure you factor these extra costs into your budget.

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Do I need planning permission to build a bedroom extension?

Many home extensions fall under what is known as ‘permitted development‘. Provided your plans meet all the conditions for this, you may not need planning permission. Remember though that your extension will need to meet building regulations.

Do I have to use an architect or structural engineer for my extension?

You don’t necessarily need an architect for your extension project, but a structural engineer could prove invaluable. As your project involves the stability of a building, it’s important to get it right. An expert can provide you with structural calculations and drawings which the building contractor will use during the project.

How long does it take to build a bedroom extension?

It can take around three to four months to complete this kind of project, depending on whether your extension is single or double-storey.

But the timescale will largely depend on existing utilities in the extension footprint, and the ground conditions for the foundations. It also depends on how long the reinstatement work takes. This refers to fencing, paths and gardens around the new extension.


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