How much does a London basement conversion cost in 2023?

Mar 21, 2023 | Property News

London is a densely populated city where above-ground space is at a premium. Creating space underneath the existing building is often the only way to increase the usable square footage of your home, and basement conversions have become increasingly popular with homeowners in the capital as a result.

The extra space can be used for a variety of purposes, ranging from a home office or children’s playroom, to a wine cellar or luxurious spa and swimming pool, and the additional floorspace can add significant additional value to your property. Successful basement conversions can create spectacular spaces, but such projects require considerable project management alongside construction expertise and creativity with interior design.

How much does a basement conversion cost?

The cost of creating a basement extension will vary significantly between projects. Whether additional excavation is required, or if you will be making major structural alterations, it can have a major impact on the final price;  alongside other elements such as the ground make-up of the site and the relative location of neighbouring properties.

As there are so many factors involved in a basement conversion, it is best to discuss your needs with a qualified team with the right expertise and experience from the start. Good London Builders can guide you through the process from start to finish, from selecting the right team of structural engineers, planning consultants, party wall surveyors, and building control specialists to coordinating all the materials and fitting the final fixtures.

What affects the price of a basement extension?

Planning applications

Planning regulations are complex. To make sure that you get the right permissions for your basement construction, it is best to employ an experienced planning consultant with knowledge of your local planning department. We have experience in managing basement conversions and major structural refurbishments across west London, including Battersea, Chelsea, Clapham, Fulham, Kensington, Pimlico, Southwark, and Wandsworth and can help you to apply for the right permissions.


Each part of London is different, and the expense of expanding down beneath a building can vary significantly due to the ground make-up, water levels, and relative location of neighbouring properties to the area.

Basement design and purpose

A room beneath your property should ideally be as flexible an addition as one constructed above ground. A successful basement design will minimise hallway space, provide seamless access to the new basement floor from your current home, and make the most of opportunities for natural light.

Construction expertise

A basement conversion is a complex project, especially if excavation is needed to create a space larger than the property’s current cellar and major structural reinforcements are required. Some basement conversions will call for mass concrete traditional underpinning, whilst others might need reinforcement with continuous flight auger (CFA) piles. Almost all below-ground projects will involve damp-proofing and considerations around drainage. We will take into account all these elements and hundreds more to make sure we find the right people with the knowledge and expertise to complete your basement extension to the highest standards.


Basements can be constructed with brick, concrete block, poured concrete, pre-cast concrete, or even treated wood. We take care of logistics to make sure that these materials, alongside the various fixtures and fittings, arrive on-site at the right time and at the right price to ensure the construction can continue without delay.

Interior design

The architecture and build creates the right shell for a successful basement conversion, but it is interior design that completes the look. We work with our clients to find an interior designer that matches their tastes to help them create a spectacular new space that is sympathetic to the design of the rest of their home.

If you are looking to convert your existing cellar into a new living space or would like to explore your options to excavate a new basement, then contact Good London Builders today on 0207 978 5097.

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