Completed basement conversion

How Much Does A Basement Conversion Cost?

When it comes to making a house a home for your family, you can never have too much space. Space lets households relax and spend their time wisely, without being on top of each other. Despite this, not everyone has the luxury of owning a large or spacious home. Families that wish to reside in big cities like London, for example, may have to settle for a home that is smaller than they would like due to house prices. There are a number of ways, though, to make your home or property feel and look more spacious, with basement conversions being just one viable option. Basements can be transformed and utilised for a wide range of reasons, where you need a home office, a playroom for your children, a home gym or simply an extra living space for family members to relax away from the chaos of your main home.

Many homes may have existing basements that have been neglected over time or simply used as storage areas and not habitable rooms. Or, you may not currently have a basement but wish to build one from scratch. Either way, when considering ‘how much does a basement conversion cost’ it’s important to take into account the wide range of costs that come with taking on the task of a basement conversion. Think about the building, damp proofing, decorating and more, all tasks that will require a budget either for materials and tools or to employ professional help to take over. Let’s take a look at the main costs to consider.

All that being said however, as a rough guide you can expect a to spend around £1000 per square metre for a basement conversion.

What Else To Consider

As we’ve mentioned, there’s a lot to consider when it goes into calculating the price of your basement conversion, you’ve got building regulations, damp and waterproofing, insulation and heating, ventilation, lighting and more! In the below sections we will dig deeper into these elements so you can better understand the work that goes into a basement (cellar) conversion.

Building regulations

If your basement or cellar is currently unused and not habitable, you will need to make sure it is regulated by professionals to ensure complete safety before and after your project. You must adhere to Building Regulations if you want to avoid fines, ensure that your basement can be heated and lit efficiently and that it is a safe space to spend time.

Be prepared for unexpected costs to crop up at this stage, as regulations can flag up issues with ventilation, fire safety, energy efficiency, electric wiring and damp that will most likely need professional help to fix.

On top of this, consider the walls that will be affected if you plan to build a new basement or adapt the structure of an existing one at all. If you will be building on or next to a ‘party wall’ – one that connects two houses together – you will need to inform your neighbours about the work being done and come to an agreement. If the local authorities are involved to help the two parties reach a reasonable agreement, you will need to be prepared to pay up to £700, so its best to work with your neighbours and keep on their good side!

Damp and waterproofing

If you live in an older home or have a basement that is largely unused due to damp, it will likely need to be waterproofed professionally. Low-level or below ground level rooms are far more prone to damp and flooding due to the moisture in the air and ground. For this reason, you must be prepared to protect your basement from damp and mould when transforming it into a habitable space. While there are DIY damp proofing kits available online, it is far safer to invest in professional damp removal or prevention services to make sure your basement is protected and free from potentially harmful mould, rot or damp. Allerton Damp Proofing are leading experts in damp proofing and removal for properties across the UK, specialising in property surveying and basement conversions to help people transform their dingy and damp downstairs areas into a warm and cosy space to spend time.

If your basement has already been regulated and you have recently had damp proofing experts take a look around your home, you can skip these costs, though it’s always better to be safe than sorry. If damp is left to spread and turn into mould it can release dangerous spores into the air which can wreak havoc for those with existing lung or skin conditions and, in some cases, even lead to serious health issues.

Insulation and heating

Heat rises – so naturally, the temperatures below your house will be far lower than at the top, making basements colder places to spend time. Houses with basements already built-in may already have insulation installed throughout, but if your insulation is decades old or you are building a new basement, adding high-quality and thorough insulation is another cost to take into account.

The purpose of insulation is to stop the cold air from the outdoors or ground reaching the walls of your home and prevent the warm air from escaping. On the other hand, as well, good insulation methods should also have a vapour control layer to stop warm air reaching the wall and forming condensation. If not, the moisture on your walls can lead to damp and even rot which can damage the structure of your home.

On top of the insulation, you will need heating methods installing to make sure your basement is a cosy space and doesn’t require several layers. Radiators and electric heaters, as well as underfloor heating if you have a larger budget available, are all great options to transform a previously cold area into an inviting room.


If you plan to use your basement as a gym, office, or room that will be commonly used, you will need to make sure there is plenty of ventilation. Windows, doors, or extractor fans are all ways to

increase the airflow around your room, prevent excess moisture and avoid damp forming. Not only will this keep your room in good condition, it will make it a safe and far more pleasant space to be.


Finally, think about how much you will need to spend on lighting. The majority of basements will receive little to no natural light from the sun, making it essential to install ceiling lights, wall lights, and/or plenty of lamps.

In Summary

Overall, there is a wide range of costs and factors to consider when deciding to renovate and convert your basement. If your basement is in particularly poor condition or you are building a new basement from scratch, you will need professional help to make sure your basement is properly regulated and safe. For a rough guide though, you can expect to spend around £1000 per square metre.

Despite the costs that can quickly add up when converting a basement, a habitable and attractive basement room can add huge amounts of value to your home – particularly valuable if you ever decide to move and sell your home.

About Mat

A complete novice trying to navigate in the world of DIY. I bought my first home about 2 years ago & ever since I've been trying to research & learn how best to tackle common household problems.

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