Guide
Basement waterproofing: Type A, B and C under BS 8102, and what each costs
Updated
Basement waterproofing in the UK is designed to BS 8102:2022, which sets out three ways of keeping water out of a structure below ground: a barrier applied to it, a structure that is watertight itself, and a drained cavity that lets water in behind a membrane and pumps it away.
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The three types
BSI's own page for BS 8102:2022 says the code covers waterproofing barrier materials applied to the structure, structurally integral watertight construction and drained cavity construction. The trade calls them Type A, Type B and Type C.
Source: BSI: BS 8102:2022, protection of below ground structures against water ingress
- Type A, barrier (tanking)
- A cementitious slurry or membrane applied to the walls and floor, inside or out. The lowest cost per m², but it needs a sound wall and lower water pressure.
- Type B, structurally integral
- Waterproof concrete that resists water itself. It is built in when a basement is constructed, not added to an existing cellar.
- Type C, drained protection
- A studded cavity drain membrane that carries water that gets past the wall to a drainage channel, a sump and a pump. The usual choice for habitable space and higher water tables.
Those definitions are MPS Concrete's, on its own price page, which also notes that the most reliable schemes combine systems so that one backs up the other.
Source: MPS Concrete: Basement Tanking Cost UK
What each type costs
| Type | Rate per m² | Firm | Source |
|---|---|---|---|
| Type A tanking | £40 to £80 | North London Damp | North London Damp: Basement Waterproofing Cost Estimator |
| Type A tanking | £50 to £100 | MPS Concrete | MPS Concrete: Basement Tanking Cost UK |
| Type C cavity drain | £70 to £140, plus the sump pump system | North London Damp | North London Damp: Basement Waterproofing Cost Estimator |
| Type C cavity drain | £80 to £150 including sump and pump | MPS Concrete | MPS Concrete: Basement Tanking Cost UK |
Building regulations and planning
Approved Document C is the government's statutory guidance on resistance to moisture under the Building Regulations in England, covering the floors, walls and sub-soil drainage a basement depends on. Turning a cellar into living space is building work, so ask your contractor how its design meets it.
Source: GOV.UK: Approved Document C, site preparation and resistance to contaminants and moisture
The Planning Portal says converting an existing basement into living space is unlikely to need planning permission, but creating a new basement commonly does, as does adding a lightwell, altering the outside of the property or creating a separate dwelling.