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Basement Specialists

Basement Conversions

Refurbishing your home or a property you own can be one of the most exciting projects you undertake. Often, especially in London, the high cost of moving homes makes refurbishment of your existing property the more sensible option.

With space at a premium these days, high property prices and soaring stamp duty rates, we have seen an increase in extensionsloft conversions and basement conversions, particularly in South West London, as a way to increase the living area of a home. Whilst extensions and loft conversions have been common, basement conversions in the London area are relatively new, but increasingly popular route to include areas such as wine cellars, cinema rooms, gyms and home offices. The SDA Build London team are specialists in basement conversions, being the builders of choice for basement conversions in the Chelsea, Kensington, Fulham and surrounding areas.

types and costs of basement conversions

Existing cellar

Do you already have an existing space in your basement that you want to convert into something habitable? If a space already exists, this is the best-case scenario of a basement conversion as the heavy-lifting has already been done. The cost of converting an existing cellar into something more usable would be approximately £2000 per m2, depending on the specs you choose. The costs will increase if you need to increase the head heights or lower the floor.

wine cellar conversion
media room

Basement excavation

If you need to excavate a basement, naturally the costs will be higher simply because the amount of work required will be more. The specific areas that will need to be costed are:

  • Removal of excess material under the home. You will need to factor in digging equipment, skips and additional labour.
  • Tanking and waterproofing. This is the single most important aspect of a basement conversion. Find out why.
  • Underpinning walls
  • Rerouting drains
  • Adapting to ground conditions which may only be revealed once your builder starts excavating
  • Adapting to water table levels.

You should expect the cost of a new basement excavation to be approx. £3000-4500 per m2.

Use of Basement

What will the room be used for? This is a vital factor in determining the cost. Basements are used for a variety of rooms including, gyms, cinema rooms, garden rooms, kitchens, playrooms, swimming pools and others. The cost of building any of these will depend on the specs you choose.

External Access

Do you require external access to the basement? This will add to your cost as a separate entrance and full access path will have to be excavated and created. It would be more cost-effective to have access from within the house, however, that may not always be desirable.

Other costs

There are other costs you need to consider and factor in your overall cost of build.

Architect Fees – Please read our guide on Choosing the Right Architect.
Planning Applications
Structural Engineer Fees
Building Regulation Fees – Find out about more about Building Regulations for Basements.
Party Wall Agreements

A basement conversion can add valuable space to your property, however, it’s important to consider all the elements mentioned above when you are working out the costs. If you’d like a handy tool to help you plan your project, please download our FREE project management checklist.

If you’d like to have a look at some of the basements we’ve built (and we’ve done a fair few), please visit our Projects page on our website, or DOWNLOAD our latest brochure to inspire you to get on with your basement conversion.


Book a free consultation in the comfort of your own home and share your design ideas with us. Our team will then come up with a unique solution for you and your home.

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If you’d like to look at some of the work we have done, why not download our latest brochure? We’re almost certain it will inspire you to get your property refurbishment project going.