“How much does a basement conversion cost?” is one of our most common questions. The honest answer is that it depends on the space, its condition and what you want to use it for. These are the factors that make the biggest difference.
1. The waterproofing system
Below-ground rooms need a properly designed waterproofing system. The two main approaches are a cavity drain membrane, which manages water and directs it to a drainage point, and tanking, a barrier applied to the walls and floor. Many projects combine both. The right choice depends on the ground conditions, the water table and how the space will be used.
2. Drainage and pumps
Cavity drain systems usually need a drainage channel and often a sump pump to remove water. Pump stations, back-up pumps and alarms all add to the cost but are what keep the space dry long term.
3. Headroom
If the existing ceiling height is low, increasing it means lowering the floor, which is a structural job involving excavation and underpinning. It is the biggest single factor in cost, and needs structural engineers and building control approval.
4. The condition of the existing space
Existing damp, decayed timber, failed old tanking, or structural cracks all need to be dealt with first. A survey will identify these at the start, so there are no surprises later.
5. Finishes and services
Insulation, plastering, flooring, lighting, heating, ventilation and any kitchen or bathroom all affect the final figure.
6. Access
Tight access, removing spoil from the site and working in terraced or listed properties can all add time and cost.
Getting an accurate price
The only reliable way to price a conversion is a site survey. We are members of the Basement Waterproofing Association and provide a fixed, written quotation after inspecting the space. Learn more about our basement and cellar waterproofing.
