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Cellar & Basement Conversion specialists - what you need to know

Basements and cellars are all too often missed opportunities, with the potential to add real value to your home. Conversions can unlock this potential, transforming underground spaces into useable rooms to suit your needs. Whether you’re looking for a guest room or granny flat, a larger kitchen or somewhere to let that gym equipment gather dust… a conversion may be the answer.

The precise nature of the conversion will depend on your plans for the space but regardless of its intended use, your new basement will need damp-proofing. Heating and ventilation systems must also be installed, to ensure the space is safe and comfortable.

Though many period properties will have basements, they are mostly cramped spaces intended purely for storage. Your builder may therefore need to dig down substantially to increase the head height. You will want to be sure your new basement isn’t claustrophobic and that any new rooms adhere to building regulations regarding minimum head height.

You may choose to extend your current basement beyond the original footprint of the house or building. With the right guidance, extending out beneath a garden can be a great way of maximising space. This may also allow your builder to incorporate light-wells into the design, which is an excellent way of introducing natural light into your basement. 

If there is no existing basement or cellar in your property, major excavation work will be necessary to create one from scratch. Along with any excavation, a new staircase will be added and your builder may also need to underpin any party walls.

Cost of cellar and basement conversion work

There are significant variables when it comes to costing – namely the extent of structural work required, access and ground conditions. The cost of damp-proofing, for example, will be dictated by the condition of your basement to begin with. If you’re looking at additional features, such as light-wells or bathrooms the extra work entailed will increase costs significantly.

For the most basic basement conversion, where no digging down or underpinning is required, it is advisable to budget £600-£1200 per square meter. If your basement floor needs lowering, costs will rise to between £1650 and £2200 per square meter. For basements created from scratch, quotes will be in the region of £2500 - £4000 per square meter.

The qualifications your tradesperson needs

Basement and cellar conversions can be carried out by reputable builders, often working in tandem with structural engineers.

Some builders will carry a card from the Construction Skills Certification Scheme. If your builder lists any specific qualifications it’s always a good idea to ask for proof of these before work begins.

There are various official trade bodies in the UK and it‘s advisable to check that your builder is registered with one of them – it’s not a necessity but is usually a good indication of how reputable they are. Each body has its own set of criteria, which must be met to qualify for membership.

You can find more detailed information about the different qualifications an experienced builder might have here. 

Planning permission for cellar and basement conversion jobs

Unless there is significant change to the external appearance of the building, planning permission is not usually required for basement or cellar conversions. This will obviously differ for listed buildings, or those in conservation areas.

You are likely to need planning permission where major excavation work is required to create a new basement, or where your basement is to serve as living accommodation. Further information can be found here. 

Insurance for cellar and basement conversion work

Public liability insurance is a requirement of any reputable tradesperson. This protects against any accidental damage to your home.

Questions you should ask your tradesperson

• Do they have public liability insurance?
• Do any of the planned adjustments require planning permission?
• Does the basement design adhere to building regulations (namely ventilation / fire escape routes / ceiling height)?