Basements & Cellars: Understanding Your Options
Basement and cellar waterproofing is a specialist discipline in its own right, governed by its own British Standard. We don't carry out tanking or structural waterproofing ourselves — but if you're weighing up your options, here's what the standard actually says, in plain English.
Why below-ground spaces are a different problem
A basement or cellar sits below the water table, or close to it, and is exposed to groundwater pressure in a way that above-ground walls simply aren't. That's why below-ground waterproofing is covered by its own dedicated standard, BS 8102:2022, rather than the guidance that applies to rising or penetrating damp elsewhere in a property.
The three system types
| Type | What it does | How it works |
|---|---|---|
| Type A — barrier | Stops water reaching the structure | A tanking membrane or coating applied to the walls and floor |
| Type B — structural | The structure itself is watertight | Reinforced, waterproof concrete built to resist water ingress |
| Type C — drained | Manages water that does get in | A cavity drain membrane channels water to a sump and pump |
An important point BS 8102:2022 makes clear: for a habitable basement, combining at least two of these types is generally recommended. No single system is treated as foolproof on its own.
The honest caveat about Type C systems
A drained (Type C) system doesn't stop water entering — it manages it, channelling it to a sump and pump. That means it depends entirely on ongoing maintenance: the pump has to work, any alarm has to be tested, and a battery backup needs to actually function if the power goes. A drained system that isn't maintained doesn't fail loudly — it just quietly stores water out of sight instead of dealing with it. If a basement conversion is on the table, this maintenance requirement is worth understanding before, not after, the work is done.
Questions worth asking any waterproofing specialist
- Which type, or combination of types, are you specifying, and why for this particular basement?
- What's the maintenance requirement, and who's responsible for it once the work is finished?
- Is the specialist certified under a recognised scheme for structural waterproofing design?
- What happens if the sump pump fails — is there an alarm, and is there a battery backup?
We don't carry out basement tanking ourselves, but we're happy to point you in the right direction, or help if damp above ground level is also a concern.
Get in Touch →Frequently Asked Questions
Type A is a barrier — a membrane or coating applied to keep water out. Type B relies on the structure itself being built as watertight, reinforced concrete. Type C doesn't try to stop water entering at all; it manages what gets in via a cavity drain membrane leading to a sump and pump.
BS 8102:2022 generally recommends combining at least two of the three system types for a habitable space, since no single system is treated as completely foolproof on its own.
Yes. A Type C drained system manages water rather than blocking it, so it depends on the pump working, any alarm being tested, and a battery backup functioning if the power fails. Without that maintenance, problems can go unnoticed rather than being prevented.
Often, yes, but it requires proper waterproofing design specific to the space, usually a combination of system types under BS 8102:2022, and should be specified by a suitably qualified waterproofing specialist rather than treated as a standard damp-proofing job.