Usually, yes. Most cellars can be converted into dry, usable space with a properly designed waterproofing system, often a cavity drain membrane with drainage and a sump pump, alongside ventilation, insulation and the right approvals. The waterproofing design is the critical part.
A converted cellar can be the best room in the house: a home office, a gym, a playroom, a snug. I’ve converted plenty, and the difference between a good one and a bad one is all in the waterproofing.
Start with an assessment
A cellar is below ground and the ground around it is often damp or wet. Before anything is designed, the cellar needs a survey to understand the risks: the walls and floor, any water coming in, the water table, nearby drainage and what you want to use the space for. BS 8102, the British Standard for protecting below-ground structures against water ingress, sets out how that risk should be assessed and the grade of dryness needed for different uses. A habitable room needs a high grade.
The waterproofing
- Drained protection, a cavity drain membrane, is often used in older cellars. A studded membrane on the walls and floor lets any water that comes through drain behind it to channels and a sump, where it’s pumped away. The room side stays dry.
- Barrier protection, often called tanking, uses waterproof coatings, renders or slurries bonded to the walls and floor to hold water back.
Sometimes a combination is used. The right system depends on the building and the survey.
Sumps and pumps
If the system relies on pumping, the pump is critical. A good installation will have a properly sized pump, a backup pump, a high-level alarm, and often a battery backup in case of power cuts. Pumps need regular servicing. A failed pump in a converted cellar can lead to flooding.
The rest of the job
- Ventilation. Below-ground rooms need it, both to control condensation and for air quality.
- Insulation, heating and lighting.
- Head height, escape routes and fire safety.
- Building regulations approval is normally needed for converting to habitable space. Check with your local authority’s building control about what applies to your project, and about planning if you’re changing the outside.
Things to avoid
- Painting a waterproof coating onto unprepared brickwork and calling it done.
- Systems with no drainage route for water that does get through.
- Pump installations without backup or alarms.
Get the waterproofing right and the rest is just a nice room.
When to call a specialist
If you're thinking about converting a cellar or basement, get a survey from a CSSW-qualified surveyor before you plan anything else. Book a survey with All Dry on 01226 287181 or email info@alldrydampproofing.com.
Related video from Damp Sam
Listen on The Damp Show
Frequently asked questions
Do I need building regulations for a cellar conversion?
Converting to habitable space normally needs building regulations approval; check with building control.
What is BS 8102?
The British Standard for protecting below-ground structures from water ingress.
Do basement sump pumps need a backup?
A backup pump and high-level alarm are strongly recommended in case the main pump fails.