How to create a basement room

Get the extra space you need by building another room underground

How much will a basement cost?

If you already have a cellar or basement to convert, you can expect to pay from £10,000 to £30,000. If, however, you need to dig out a new basement from scratch, this can cost from £40,000 to £100,000.

Costs will be at the higher end if, for instance, you live in an older building that might require underpinning or if there are drains beneath your house that need moving.

If you use an architect, they will usually charge from 12 to 15% of the build fee on a small project, and 7 to 8% on a large one.

Do I need planning permission?

If you live in a flat, you’ll definitely need to apply for planning permission. If you’re in a house, it may not be needed if you already have some sort of space in your basement, as the work should fall within permitted development.

However, if your house is on a flood plain or at risk of flooding, it’s likely you’ll be refused planning permission. You’ll have to get Building Regulations Approval, and if your home is listed, you’ll need Listed Building Consent. For more information of what is required, visit www.planningportal.gov.uk.
Who should do the work?

It’s good idea to get an architect to make sure your new basement is well designed and that it gets enough light.

Once your architect has drawn up general plans, then a structural engineer will need to check them.

Finally, you can call in either a dedicated basement contractor or a reputable builder to carry out the building work. The former usually costs more.

Is it a big job?

Building a basement conversion is a big job and it can take anywhere from 1 to 12 months to finish.

If you don’t have an existing cellar, the new basement will have to be dug out and a support put in place. You’ll have to pump water out of newly dug out cellars and existing ones if they’re damp.

The new room will usually then have to be waterproofed either by using a membrane or, for very damp spaces, a permanent drainage system whereby water is constantly pumped away. The whole process is called tanking.

You’ll also need to install central heating or underfloor heating.

How to use your basement space

There are loads of ways to make the most of your basement conversion. If you already have a big kitchen, you may want to use your new space for:

An extra room

You may recoup the cost of adding a games room when you come to sell, but an extra bedroom could add as much as £10,000 to the value of your home, and an office could add £20,000. The room will need to have a bright, ground-floor feel to increase value.

A utility room

If you have a dedicated room for your washer and dryer, you’ll free up space in your kitchen, but the downside is that it might not add much value to your property.

Useful contacts

These companies can help with your project:

Architect Your Home offers a pay-as-you-go service

Royal Institute of British Architects for architects in your area

The Basement Information Centre offers information on development and use of basements

See ideas for creating more space in your home, including building a side-return extension and loft conversion.

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