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Bird view of façade elevation with timber of smart passive house in Royal Borough of Kensington and Chelsea of London

Basement Conversions

Basement Conversion in London

A basement conversion can create a range of possibilities within your home, from a simple spare room to an entirely new storey. It is also ideal for homeowners looking for more room without compromising on their outdoor space.

​Pros of Having a Basement Conversion in London

Many people assume that their basement can’t be used as a suitable living area yet our expertise allows us to design warm, light-filled basement conversions that add depth and character to your home.

LXG-ATG-00-XX-PH-A-0038-Staircase and Bathroom view

How Much Does a Basement Conversion Cost

in London

It can help to have an idea of how much your basement conversion costs as an average. It’s important to always keep in mind that many variables can add to the average cost; other conditions can make the cost lower. Make sure you work with the right company that can support you making the choices that are best for you, also considering your budget requirements.

Baseline costs of construction in London, which don’t include professional fees and finishes like flooring, windows, doors, furnishing and joinery, fittings etc:

  • Creation of a new basement under an existing building: £3,000 to £5,000 per sqm

  • Conversion of an existing cellar: £2,250 to  £3,750 per sqm

  • Extension of an existing basement/cellar to the garden: £2,500 to £4,000 per sqm

Planning Permission for a Basement Conversion

For basements in London, permitted development is restricted to not substantial alterations. You can convert an existing cellar or basement into a living space within permitted development rights. Any excavation for a basement requires planning permission. Approval rate for basement conversions planning applications is very high, because councils usually grant permission. The process for the application, though, is a bit more complex, due to the amount of required documentation, reposts, investigations and other conditions that are specific to basement applications. The final result is very predictable, but the process to get there is usually longer and has higher cost than applications for standard extensions  like loft conversions or rear extensions.

LXG-ATG-00-XX-PH-A-0018-Kitchen and Living Room

Architectural Designers for Basement Conversion in London

Our team of experts would be glad to help you with your journey to achieve your dream for your basement. We have designers who will be able to help you with your design process, planning application, building regulation package, structural package and also the build stage. Please feel free to get in touch with us to use your free 30 minute consultation and we will help you through the process.

An example of

Basement Conversions Projects

that we have done.

9 Lexham Gardens Mews

Construction Status:
Development Area:

January 2021
London, UK
Garage and Outbuilding Conversions
65 m2


they wanted to replace the garage with a smart passive house that looked like a garage. We designed this smart house with consideration to every little detail.

Bedroom and metal staircase of the new-built smart passive house as an architectural garage conversion in Royal Borough of Kensington and Chelsea of London
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