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  • Neil Harrison

What about a Basement extension? - an ideal project which can add value to your home - but what m...

Updated: Jun 24, 2023

A good few different types and styles of property all offer the potential for the valuable extra living facility of a basement extension. We, at Mint, of course, appreciate how valuable a home extension a home basement can be to many homes, and there are some excellent basement extensions on view in our 'home' town of Cheltenham and indeed right across our local Cotswolds area.

We noted the high profile, ever informative, HomeOwners Alliance has been offering some timely basement extension advice in their recent Newsletter. The Alliance’s expert team quite rightly indicate that a basement extension for sure can be a fantastic way to expand living space, creating an extra bedroom, TV lounge, office or gym and what's more in doing so add value to most homes!

ins and outs

They schedule in their newsletter here - some valuable guidance on the ins and outs and challenges of a successful basement home extension.

Indicate the HomeOwners Alliance - “The costs and complexity of a basement project will vary dramatically depending on whether you have an existing cellar with enough headroom that can be easily converted or whether you will need to excavate to make the space workable.”

cost indications

A rough rule of thumb, they say, is that a basement conversion is likely to cost between £900 to £1,400 per square metre if it is an existing space with no structural changes needed. For projects that require excavation and underpinning the cost is likely to range between £1,500 and £2,000 per square metre.

guiding hand

The Alliance indicate that as a priority it is advisable to speak to your local planning authority and building control department before you start any work to make sure you know exactly what permissions are required. If you have a basement home extension in mind, of course, we at Mint are very much on hand to guide and assist and ensure you are well-informed about all aspects of your planned basement extension project.

planning permission?

It is true, you will almost certainly need planning permission if you are making any structural changes, altering the external appearance of the property or if your home is listed or is in a conservation area. If you are making structural changes and share a wall with your neighbour you will need a Party Wall Agreement.

adding value

A key question with all home extensions, whether basement or not, is will the project add value to your property for the future. The HOA indicate, quite rightly, that an extra room, such as a converted basement, can increase your property value by up to 20 per cent.


The Alliance go on to suggest that home-owners should speak to a couple of local estate agents before starting a basement project and get them to indicate whether they feel in the current housing climate you will recoup your investment when it comes to selling you home in the future.

specialist issues

With basements there are specialist issues to consider - one very very vital one is ensuring there is a good source of natural light and decent ceiling height in your new renovated basement. These features can very much help to ensure that your conversion is a worthwhile investment that really does boost your home’s value. The more light is the more right – one might say!

rising costs

Also, say the HOA, there just might be certain factors that can push up your basement conversion costs. These can include requirements such as having to divert drainage or if where your home is located, has a high water table, which means you need a pump to be working constantly during the project.

‘ground’ effects

What’s more, if your property sits on certain types of ground such as clay, sand, marsh or made-up ground extra costs can also occur. (Note - made-up ground is also known as 'fill' or man-made ground, where levels have been altered or filled in using building waste and previously excavated material.)

here to help

Other issues might be a difficult access, nowhere to store excavated soil or a street with high parking demand, which might mean you can’t get permission for a vital skip. Lots to think of it seems, but if you have a basement plan, as already said, we at Mint can assist in all respects as with any home extension renovation or refurbishment project you may be considering.

For lots more detail on key aspects affecting your basement project project plans, get further information here:-

Refurbishment, improvement and extension of your home, including a 'room' in the garden, Mint offers a full development and finishing service to add value to your home for 2020. We are here to help with any questions or concerns you may have. We have all the expert contacts on hand to help you.

Whatever your needs, please request your quotation to improve, refurbish or extend your home. Contact Mint Builders on 01242 279739or email

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