What Does Basement Waterproofing Cost?
Quick Answer
Cavity drain membrane £80–150/m². Tanking slurry £30–60/m²
Installed prices including labour. Cavity drain is the preferred method for habitable basements.
Waterproofing Methods Compared
- Cavity drain membrane (Type C): £80–150/m² — studded membrane creates an air gap, water is channelled to a sump pump. Most reliable for habitable rooms.
- Cementitious tanking (Type A): £30–60/m² — multi-coat slurry applied directly to walls. Good for light damp but relies on a complete bond.
- External waterproofing (Type B): £150–300/m² — membrane applied to the outside of the structure. Only practical during new build or excavation.
- Combined systems: Often the best approach uses Type A + Type C together.
Typical Project Costs
- Small cellar (15m²): £3,000–6,000 (cavity drain)
- Standard basement (30m²): £6,000–12,000 (cavity drain)
- Large basement (50m²): £10,000–20,000 (cavity drain)
Additional Costs
- Sump pump and chamber: £1,500–3,000
- Battery backup for pump: £500–1,000
- Floor drainage channels: £30–50/linear metre
- Maintenance contract: £150–300/year
BS 8102 Classification
The British Standard BS 8102 classifies waterproofing by protection type:
- Type A (barrier): Tanking slurry, membranes applied to structure
- Type B (structurally integral): Waterproof concrete (e.g. Sika watertight concrete)
- Type C (drained): Cavity drain membrane with managed water
For habitable rooms (Grade 3 use), BS 8102 recommends using at least two types of protection in combination.
Last updated: April 2026