Basement Extension Builders in South West London

If you are planning to build a luxury basement in South West London, or to turn your cellar into a lounge, a games room or a home cinema, our team of expert builders can add an extra level to your home by creating bespoke living space beneath your house. As one of the leading builders in South West London, we are fully insured and have years of experience building basements in London. We work along with building inspectors who check every step of the construction process to ensure that all the correct procedures are followed and that the basement and the rest of the house remain structurally safe.

Cellar conversions

If you have a cellar where the ceiling height is at least two metres, you could easily turn it into a cosy basement room by renovating the interiors and adding lights and ventilation. You might still have enough space left to keep a few bottles of wine there, and by turning your new space into a lounge or sitting area, you will never have to carry the bottle up the stairs again.

Half basements

If your property sits on a slope, you could take advantage of this by building a semi-basement, with part of the new area sat below the ground. Since you can add windows and sometimes even sliding glass door to half basements, it is much easier to bring in air and natural light. You might even be able to extend the space into the rear garden, creating even more extra room.

Full basement extensions

When building a full basement, the whole new area will be below the ground level. It involves excavation, underpinning, waterproofing, tanking and under-structure construction. Basements are good at absorbing noise, which makes them the perfect space for home cinemas, playing music, or practising the drum kit without disturbing the neighbours.

What you need to know before building a basement in London

Cost

An average basement extension in London costs around £5000 per square metre. A large part of this figure is down to the groundwork: excavation and underpinning the foundations of the existing house. In prime South West London locations such as Richmond, Barnes and Kew, building a basement is still a lot cheaper than moving into a larger house.

Planning

If your property is a terraced or a semi-detached house, the Party Wall Act procedure requires you to serve a notice to your neighbours. The foundations of adjoining dwellings might need structural work to keep them stable during and after the project. An architect will have to carry out a survey before preparing the structural and architectural plans.

Waterproofing

Underground water will potentially cause pressure on the basement walls exploiting any weaknesses in the waterproofing, which could ultimately lead to the basement being flooded. This problem can be solved by running a land drain around the whole perimeter of the basement and pumping out any water collected there. Or, you can construct a cavity within the wall to trap the water and allow it to run down to a drain.

Ventilation and Natural Light

Basement rooms need to be adequately ventilated, as set out in the Building Regulations. If there is no possibility of providing opening windows, the easiest way to circulate a supply of fresh air is to install a mechanical ventilation system. Another way to provide ventilation and daylight is to lower the garden and install sliding glass doors onto a small patio with the steps outside the basement leading up to ground floor level.

Basement extensions at a glance

Who we are: Richmond Traders Ltd, a building and construction company based in Richmond, South West London.
What we do: basement excavation, conversions, underpinning, waterproofing and fit-out to create new living space.
Where we work: Richmond, Twickenham, Kingston, Hampton, Isleworth, Teddington, Ham, Petersham, Sheen, Barnes, Kew, Ealing and across London.
Related services: House extensions, Design and build, Planning and regulations.

To discuss your project, contact Richmond Traders for a site visit and an itemised quotation.

Frequently asked questions

Do I need planning permission for a basement extension?

It depends on the property and the local council. Many basement projects need planning permission and a party wall agreement, and all need Building Regulations approval. We guide you through the process.

How do you keep a basement dry?

We design and install a suitable waterproofing system, such as cavity drainage membranes or tanking, to keep the new space dry.

Can you convert an existing cellar?

Yes. We can lower floors, underpin walls, waterproof and fit out an existing cellar as usable living space.

Which areas do you cover?

We cover Richmond, Twickenham, Kingston, Hampton, Isleworth, Teddington, Ham, Petersham, Sheen, Barnes, Kew, Ealing and across London.