A basement extension is a great way to add extra space to your home. Sometimes it can be the only option if you live in a place that isn’t too big and can’t be extended in another way. Property prices in the UK are quite high, therefore, it’s often better to add another room instead of moving. A well-converted basement can make a cosy bedroom or leisure area, it can turn into a functional office, playroom, gym or even a wine cellar. Maybe one of your children is growing and doesn’t want to share a bedroom anymore? Or maybe you’re going to work from home and need an office? Extending an attic may not always be a good idea as it’s quite far from living spaces and can be mostly used for bedrooms or bathrooms. That’s why so many people decide to convert their basement.

Costs of basement extension

You’re probably worried about how much extending your basement will cost you. This will mostly depend on whether you have a big enough basement. If you do, it can be easily turned into something else or you’ll need to excavate to be able to change something. Conversion of the basement should cost about £900 – £1,400 per square metre if you’re not excavating, and £1,500 – £2,000 per square metre if you need to make some structural changes.

You might have to pay more if:

  • you have to work on drainage or if the area has a high water table,
  • your property is placed on clay, sand, marsh or made-up ground,
  • it’s hard to access the site or there’s no place for excavated soil,
  • a lot of people park on your street and you didn’t get permission for a skip.

Adding value to your property

If you’re thinking about converting your basement to increase your home’s value it might be a good idea to talk to local estate agents. They will tell you if it’s worth investing your money in it if you’re considering selling your house. Extra room can increase the value of your it by up to 20 percent. Make sure the ceiling is high enough and your basement is full of natural light to boost the value.

Do you need planning permission?

Planning rules are different in every area and change from time to time, so make sure to contact your Local Planning Authority before you start any work. You probably don’t need planning permission if you’re not making any structural changes. However, you might need it if you’re excavating your basement, changing a structure of the building or even lowering the floor level. Planning permission is also required if you’re planning a separate unit of accommodation, you live in a listed building or in a conservation area.


Remember also to ask your Local Planning Authority if a Basement Impact Assessment is required before granting approval. A Basement Impact Assessment is required during the planning stage because recently more homeowners worry about potential structural and water damage to their houses.

What about Building Regulations approval?

Whether you need planning permission or not, you’ll have to acquire Building Regulation approval to ensure that your basement meets standards of health, safety, and welfare conditions. This covers ventilation, fire safety, foundations, and other standards. It’s best to talk to a reputable local builder who has experience in such projects. They should provide you with plans and structural drawings and will work with local authority building control to achieve building regulations approval.

Is a Party Wall Agreement necessary?

If you’re excavating your basement, you might need a Party Wall Agreement. This is required when you’re excavating within 3 metres of the property of your neighbour and lower than their foundations, you’re excavating within 6 metres and at an angle cutting across 45 degrees from the bottom of their foundations or you’re inserting beams or flashing into a shared wall. The purpose of Party Wall Agreements is to protect properties of the neighbours and it often requires sending notices to neighbours, a legal agreement and a condition survey.