CM20 Cavity Drain Membrane for Basements

Clever Shield CM20 Cavity Drain Membrane – High Capacity Type C Basement Waterproofing

Take control of heavy water ingress with the Clever Shield CM20 Cavity Drain Membrane — a high-capacity Type C waterproofing membrane engineered for demanding below-ground environments.

With a 20mm stud profile and superior drainage performance, CM20 delivers reliable protection for basements, floors, and structures exposed to high groundwater levels—helping you achieve a Grade 3 dry, habitable space in line with BS 8102.

Maximum Drainage. Maximum Protection.

• Type C Waterproofing System – Fully compliant with BS 8102:2009
• High Drainage Capacity (14L/m²) – One of the highest in its class
• BBA Certified (18/5595) – Independently tested for performance & durability
• Ideal for High Water Tables – Designed for challenging below-ground conditions
• Fast Installation – Lightweight rolls for quick floor application
• Minimal Structural Impact – No major prep or invasive work required
• Long-Term Durability – Resistant to water, salts, roots & structural movement
• Temperature Resistant – Performs in both hot and cold environments

Built for Demanding Waterproofing Projects

The CM20 membrane creates a high-capacity drainage void, allowing water to flow freely into drainage channels and sump pump systems, preventing pressure build-up against floors and walls.

Perfect for:

• Basement and cellar waterproofing
• Floor waterproofing systems
• High water table environments
• Tunnels, vaults & underground structures
• Radon barrier compliant installations
• New build & retrofit waterproofing

Product Specifications

• Stud Height: 20mm
• Water Void Capacity: 14 litres/m²
• Material: High-density polyethylene (HDPE)
• Roll Sizes:
  • 2m x 20m (40m² coverage)
  • 2m x 10m (20m² coverage | approx. 20kg)
• Application: Floors & walls (below ground)

Designed for Complete Waterproofing Systems

For best results, install CM20 as part of a full cavity drain system including:

• Perimeter drainage channels
• Sump chambers & pump systems
• Fixing plugs & sealing tapes
• Floor finishes or screed systems

This ensures a maintainable, long-term waterproofing solution that meets UK building standards.

Ideal for Converting Problem Spaces

Whether you're tackling a flooded basement or planning a full conversion, CM20 helps you create dry, usable living or storage spaces—even in high-risk environments.

Frequently Asked Questions

What is a Type C cavity drain membrane?

A Type C membrane manages water ingress by allowing it to enter a controlled cavity and safely drain away, rather than blocking it.

Why choose a 20mm membrane?

A 20mm stud depth provides greater drainage capacity, making it ideal for areas with high water ingress or pressure.

Is Clever Shield CM20 BBA certified?

Yes, CM20 is fully BBA certified (18/5595), ensuring compliance with UK waterproofing standards.

Can this be used on floors?

Yes, CM20 is specifically designed for floor applications and can also be used on walls in high-risk areas.

Is it suitable for basement conversions?

Absolutely. It’s ideal for creating dry, habitable basement spaces when used as part of a full system.

BBA

CM20 BBA

BBA Certification Clever Shield CM20 Cavity Drain Membrane 18 5595

Performance

Declaration Of Performance CM20 Cavity Drain Membrane WPDOP05 2019 08

TDS

 CM20 CDM Data Sheet