Cellar damp proofing, more accurately called basement waterproofing, keeps ground moisture and water out of the usable space below a house. Depending on the cellar and how you plan to use it, the answer may be better ventilation and drainage, a cementitious tanking system bonded to the walls, or a cavity drain membrane that collects water behind it and channels it to a sump and pump. We start by finding where the moisture comes from, because a cellar can be damp from the ground, from a leak or from condensation.
Why are cellars damp?
A cellar wall is a retaining wall with earth on the other side. In older houses it was usually built of brick or stone with no membrane, on the understanding that the cellar would be cool, a bit damp and used for coal or storage. Moisture moves through the masonry from the soil, and after heavy rain or when ground water is high, it can seep in at the joint between wall and floor or through cracks.
That is not the only cause. We often find that a cellar’s worst damp comes from somewhere more fixable:
- A leaking or blocked gully, downpipe or drain outside, pouring water into the ground right against the cellar wall.
- A leaking water supply pipe or waste pipe passing through or near the cellar.
- A blocked-up coal chute or light well collecting water.
- Condensation, when warm, moist air from the house or outside meets the cold cellar walls and floor, particularly in summer.
- Poor or no ventilation, so the space never dries.
Getting this right matters. Condensation in a cellar will not be fixed by tanking, and a leaking drain will keep soaking the ground whatever system goes on the inside.
Liverpool cellars
Cellars are common in the city’s Victorian and Edwardian housing, from long terraces to large villas. In Aigburth and around the larger houses of Toxteth, many big Victorian properties have substantial cellars, and some conversions to flats have put the cellar to new use. Some terraced houses elsewhere in the city also have smaller cellars, so it is worth checking what is under the floor before blaming the walls. Many have been bricked up, filled or forgotten, and some develop damp or rot in the timbers of the floor above as a result. We treat each one on its own merits.
How do you want to use the cellar?
The right level of protection depends on what the space is for. BS 8102, the British Standard code of practice for protecting below-ground structures against water ingress, sets out different grades of environment. In plain terms:
| Intended use | What it needs | Typical approach |
|---|---|---|
| Basic storage or plant room where some damp is acceptable | Water kept out, some dampness tolerated | Fixing outside leaks and drainage, improving ventilation, sometimes a simple drainage channel |
| Dry storage, workshop or utility | No water penetration, drier air | Cavity drain membrane or tanking, plus ventilation or dehumidification |
| Habitable room: bedroom, living space, home office | Dry, comfortable, ventilated and heated | A full waterproofing design, usually a cavity drain membrane with drainage and a sump, along with insulation, ventilation and heating; Building Regulations may apply |
We are clear with you about which category your plans fall into, because a system designed for storage is not suitable for a bedroom.
Cavity drain membranes and tanking compared
Cavity drain membrane
A studded plastic membrane is fixed to the walls and laid over the floor. Water that comes through the masonry is not stopped at the wall but runs down behind the membrane into a drainage channel, and from there to a sump where a pump discharges it. The membrane can then be dry-lined or plastered. Because it manages water rather than holding it back under pressure, it suits many older cellars. The pump needs power, a backup plan and periodic servicing.
Cementitious tanking
A waterproof render or slurry is applied directly to prepared masonry to form a barrier. It relies on a strong bond to the wall, so the substrate has to be sound and clean. It can suit some walls but can be vulnerable to cracking where the structure moves.
In many cases the design combines measures. We explain the options for your cellar, including their limitations, in a written quote.
Cellar waterproofing is not a DIY job. It involves working with a structure that holds back ground, and sometimes with old coatings or boards that may contain asbestos. We do not disturb suspected asbestos; it must be tested first by a licensed specialist.
What we check on a visit
- The walls, floor, stairs and ceiling of the cellar, including any old coatings or timber.
- Moisture and humidity readings, and signs of salts, tide marks or running water.
- The outside: gullies, downpipes, drains, ground levels, light wells and coal chutes.
- Pipework running through or near the cellar.
- Ventilation and any blocked-up openings.
- Timbers in the floor above for wet rot or dry rot, which damp cellars can encourage.
Afterwards we explain the cause in plain English and give you a written quote. If the main source is outside, such as a broken drain, we tell you what needs fixing and who would usually do it.
Damp cellars and the rest of the house
Moist air from a damp cellar can rise into the house, adding to condensation upstairs and raising humidity in ground-floor rooms. Timber joists that bear on damp cellar walls can decay. If you are seeing damp patches on the ground floor or soft boards, our damp floor repair page may also be relevant, as cellar and floor problems often go together.
What affects the cost?
We do not quote prices until we have seen the cellar. The main factors are the size of the walls and floor, the intended use, the system chosen, whether a sump and pump are needed, access down the stairs, the condition of existing walls and coatings, timber repairs, electrical work for pumps or lighting, and any finishing such as dry-lining or plastering.
Cellar work is one part of our wider damp treatment in Liverpool. If your concern is really mould and condensation in the rooms above, our damp and mould specialists covering Merseyside can look at the whole house.
Damp or wet cellar?
Call 07777 659786 or leave your details. Tell us whether the cellar gets wet after rain, how you use it now and how you would like to use it, and we will call you back to arrange a visit.
Frequently asked questions
Can a Victorian cellar be made completely dry?
Usually it can be made dry enough for its intended use, but the method depends on the cellar. Storage needs a different standard to a bedroom. Many older cellars are best treated with a cavity drain membrane that manages water rather than trying to block it. Outside leaks and drainage should be fixed first.
What is the difference between tanking and a cavity drain membrane?
Tanking is a waterproof coating bonded to the wall that holds water back. A cavity drain membrane is a studded sheet that lets water run behind it to a drainage channel and sump, where it is pumped away. Membranes do not rely on a perfect bond to old masonry, which is why they are common in older cellars.
Why is my cellar wetter in summer?
Often that is condensation rather than water coming in. Warm, humid summer air meets the cold cellar walls and floor, and moisture forms on them. Waterproofing will not solve condensation. Ventilation or controlled dehumidification usually helps, so it is important to diagnose the cause before choosing a fix.
Do I need Building Regulations approval to convert a cellar?
Converting a cellar into a habitable room, or changing its use, often involves Building Regulations, for example around ventilation, escape, insulation and electrics. Check with your local authority building control or an approved inspector before you start. Simple repairs to a storage cellar usually do not need approval.
Can a damp cellar cause rot in the floor above?
Yes. Joists and floorboards over a damp, unventilated cellar can stay wet enough for wet rot, and in some cases dry rot. If boards feel soft or there is a musty smell, it is worth having the timbers checked. See our wet rot repair page for more.