Basement Conversions

Basement Conversion London
Converting a Basement

Converting or extending basement to a home providing valuable extra living space without transforming the exterior of the house. Basement is located close to the main living areas and has a more flexible range of uses. There is no right or wrong way to set up space. You have to focus on what you want and need to decide what is your highest priority is. Start by listing the functions of the new space and what size space you will need to accommodate it. Will there be a kitchen? Will the room be a bedroom, an office, a family room, or a home theatre? Is there going to be a bathroom? Will it be a home gym?  Do you need separate rooms for all those purposes? All of these types of rooms have specific dimensions and requirements. List those out in a short “program.”

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Typical process of basement conversion:

Initial Consultation

You will meet up and discuss your needs with basement specialist or architect. You may find it easier to make a list of questions beforehand which you can refer to and make notes on. Getting indication of the costs involved.

Design and Planing

A full survey of the property is carried out and a design for proposed basement is created.

Good quality design is an integral fundamental part of sustainable development. As a matter of fact, a good design responds in a practical creative way to the function and identity of the place. Once design has been agreed, the planning permission application is submitted.

You must tell your neighbours if you want to carry out any building work near or on your shared property boundary. Basement specialist or architect will organise Party Wall surveyor to contact neighbouring properties to achieve a Party Wall award. The Party Wall Act provides a legal framework for preventing and resolving disputes in relation to boundary walls, party walls and excavations near neighbouring buildings.


Basement conversions are not a DIY job because of the risk of undermining the foundations, leading to instability or even the collapse of the supporting walls. Work on the basement is started by digging and removing soil. Underpinning and reinforced concrete works carried out and steel beams erected as required to support existing structure of the house.

Basement excavation and structural works will be followed by waterproofing the structure, reconfiguring drain runs and existing manholes. There are several ways to waterproof the structural walls of a basement. The specific method used will depend on the ground conditions and the type of construction. This is likely to be tanking, using some form of membrane, such as bonded sheet or cavity drain membranes.

Basements are naturally well insulated by the earth surrounding them, but will require additional insulation to meet Building Regulations requirements.


The key considerations for the first stage of the fitting-out process are space, comfort and light. In the words, making interior spaces suitable for occupation. Basement fit-out will involve everything from the insulated screed or polished concrete covered floors, electrics, plumbing, first and second fix items such as joinery, doors and painted finishes, organising the lighting scheme, and finally adding the furniture.

How much does a basement conversion cost and how long will it take?

Inarguably, project price depending on the size of the property, the amount of excavation and building work required and its complexity. In fact, big factors that add costs to the project are needs to divert drains, difficult or poor ground conditions, access to the site etc. Also the cost of fitting a basement reflects on the quality of the work undertaken.

Here’s a rough estimate of the costs involved:

  • Conversion of existing basement – £1,100 – 1,500 per m²
  • Lowering floor level and underpinning an existing basement – £1,500 – 2,000 per m²
  • Digging new basement space and underpinning – 2,000 – 3,000 per m²
  • New basement space beneath the garden – £1,500 – 2,500 per m²
  • Creating a light-well / external access – £5,000 – 9,500
  • Engineers fees – £1,000 – 1,500
  • Planning application – £172
  • Building Regulations application – £750 + according to the value of works
  • Party Wall surveys – £700 per neighbour
  • VAT – 20% added by a VAT-registered contractor

A high price is not necessarily a sign of quality in a building firm. But, more than that, it is important to resist the obvious temptations of a low price. If one firm comes back with a quote for your work which is significantly lower than the other tender prices, you need to be suspicious.

Although projects must meet their cost, time and quality targets. Project success can be defined in many ways, but investing in professional project management and controls can yield some very substantial benefits.

Should you require any further help or assistance, please do not hesitate to contact us.

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