Where an ordinary extension or loft conversion isn’t possible, homeowners are looking below their feet for extra room. If you already have a cellar there may be fewer obstacles than for those retrofitting a basement, but either way it is a sound investment in terms of both adding space and value.

Here, we list the typical process of a basement conversion:

Initial Consultation

You will sit down with your basement specialist or architect and discuss your needs for the proposed project. You will then be given an indication of the costs involved and offered a quotation for the structural and fit-out aspects of the work.

Design and Planning

A full survey of the property is carried out and a design for the proposed basement is created. Once a design has been agreed, the planning permission application is submitted (which should take approximately eight weeks).

While waiting for planning approval, your basement specialist company or architect will organise a Party Wall surveyor to contact the neighbouring properties to achieve a Party Wall award. Once the Party Wall award and planning permission has been obtained, you will then receive an idea from your specialist on the timeframe for each phase of the project, along with the final time for completion.


Work on the basement is started by digging and removing any soil, with any underpinning works carried out, and reinforced concrete and timber or steel beams erected as required to support the structure of the existing house, following the guidance of a structural engineer. The basement excavation will involve supporting the existing foundations, the internal loadbearing walls, floors and any concrete pads that may be supporting an existing extension.

This will then be followed by waterproofing the structure and reconfiguring drain runs and existing manholes, to ensure that you are left with a waterproof shell that’s ready for the next stage of fitting the basement out.


The fit-out of the basement will involve everything from the insulated screed-covered floor – on which you can then lay carpets, wood flooring or tiles – electrics, plumbing, first and second fix items such as joinery, doors and painted finishes that must all comply to Building Regulations standards, organising the lighting scheme, and finally adding the furniture.

Main image by Delta Membranes

Our Sponsors