What are the three types of basement waterproofing?

BS 8102:2022 defines three types: Type A (barrier or tanking) applies a waterproof coating to the structure; Type B (structural integral) uses specially designed reinforced concrete that is inherently waterproof; Type C (drained protection) uses a cavity drain membrane system that manages water ingress by directing it to a sump pump. Each has different applications, and combining systems provides the highest protection grade.

Which waterproofing system is best for a basement conversion?

Type C (cavity drain membrane) is the most commonly used system for basement conversions in the UK because it works with water pressure rather than against it, is forgiving of minor structural defects, and can be installed without external excavation. BS 8102 recommends combining two systems (e.g. Type A + Type C) for habitable basements to achieve Grade 3 (dry) protection.

How much tanking slurry do I need?

A cementitious tanking slurry (Type A) is typically applied in 2-3 coats at 1.0-1.5 kg/m² per coat. For 3 coats at 1.5 kg/m² over 100m² of wall and floor, you would need 450 kg of slurry. Always follow the manufacturer's specific application rates. The substrate must be clean, sound, and dampened before application.

Do I always need a sump pump with Type C waterproofing?

Yes, Type C cavity drain membrane systems always require at least one sump chamber with pump to discharge collected water. The sump chamber should be minimum 20 litres capacity, with a submersible pump rated for the expected flow. BS 8102 recommends a battery backup pump in case of power failure. For basements over 50m², two sumps are recommended.

How long does basement waterproofing last?

A properly installed waterproofing system should last the lifetime of the building. Type A tanking has a typical design life of 30+ years. Type B structural concrete is permanent but relies on the concrete remaining uncracked. Type C membrane systems have mechanical components (pumps) that need replacing every 5-10 years, but the membrane itself is lifetime-rated.

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Basement Waterproofing Calculator

Calculate waterproofing material quantities for Type A (tanking slurry), Type B (structural concrete), or Type C (cavity membrane with sump pump) systems per BS 8102.

Wall Area

Total internal basement wall area

Floor Area

Internal basement floor area

Waterproofing Type

Per BS 8102:2022 classification

How We Calculate This

This calculator determines material quantities for the three main basement waterproofing systems defined in BS 8102:2022 (Code of Practice for Protection of Below Ground Structures Against Water).

Type A — Tanking

Cementitious slurry is applied in multiple coats to wall and floor surfaces. Quantity = total area × coverage rate (kg/m²) × number of coats. A typical 3-coat application uses 4.5 kg/m² total.

Type B — Structural

Reinforced concrete designed to be waterproof in itself (watertight construction per BS EN 1992-3). Wall thickness typically 250-300mm, slab 200-300mm.

Type C — Drained

Cavity drain membrane (studded HDPE sheet) is fixed to walls and floor with a channel drain at the perimeter collecting water to a sump pump. Membrane area includes a 10% overlap allowance.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.