How Much Tanking Membrane Do I Need?
Quick Answer
Wall area + floor area + 10% for overlaps
A 4m × 3m basement (2.4m high) needs ~45m² of membrane (walls + floor + overlaps)
How We Calculated This
For a 4m × 3m basement with 2.4m ceiling height:
- Floor area: 4 × 3 = 12m²
- Wall area: 2 × (4 + 3) × 2.4 = 33.6m²
- Sub-total: 12 + 33.6 = 45.6m²
- Plus 10% overlaps: ~50m²
Types of Tanking System
- Cavity drain membrane (Type C): HDPE studded membrane, manages water. £15–25/m² material. Most reliable long-term
- Cementitious tanking slurry (Type A): Brush-applied waterproof coating. £8–15/m². For minor damp issues
- Structural waterproofing (Type B): The structure itself is the barrier (e.g. waterproof concrete). New-build only
Cavity Drain System Components
- Wall membrane: 8mm or 20mm stud height
- Floor membrane: Laid under screed
- Perimeter channel: Collects water at wall/floor junction
- Sump pump: Removes collected water (1–2 per basement)
- Sump chamber: Below floor level, houses the pump
Costs (2026 UK)
- DIY materials only: £30–50/m²
- Professional installation: £80–150/m² (supply and fit)
- Typical basement conversion: £1,500–£2,500/m² (complete, including fit-out)
Last updated: April 2026