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Cavity Drain Type C Waterproofing
The Type C Cavity Drain system is a reliable internal waterproofing method for below-ground structures. Instead of blocking water externally, it accepts ingress and safely redirects it. Cuspated membranes on internal walls and floors form a drainage layer, guiding water to perimeter channels and into a sump system for removal, keeping interiors dry and protected
Service information
Type C waterproofing, as defined in BS 8102:2022, is a “drained protection” system that manages water after it enters a structure. It uses internal cavity membranes to depressurise and channel water into designated voids, offering a reliable and maintainable solution.
- A typical system includes:
- Cuspated membranes (walls and floors)
- Perimeter drainage channels
- Sump and pump units
- Backup systems, alarms, and maintenance access
- Ideal for new builds and retrofits, Type C systems are used in:
- Residential basements and conversions
- Industrial and commercial buildings
- Data centres, plant rooms, and crawl spaces
- Chemical/pharma facilities
- Refurbishments with limited external access
They’re especially suited for dry, habitable below-ground spaces in residential, commercial, and industrial settings.
The cavity drain system offers passive, internal water management. Rather than attempting to stop water at the external structure, it safely collects and redirects water before it can affect the interior.
Specially designed membranes are fixed to internal walls and floors to form a free-flowing drainage void. Water is channelled into perimeter drains and directed to a sump chamber, where it is pumped away.
Often used in combination with other waterproofing strategies, Type C systems offer:
- Controlled water flow and reduced hydrostatic pressure
- Improved air quality and reduced mould or damp risk
- Long-term serviceability with minimal upkeep
- Straightforward installation, even in occupied or finished buildings
Type C waterproofing is well-suited for a variety of new-build and retrofit settings, including:
- Residential basements and cellars
- Light & heavy industrial facilities
- Data centres and IT infrastructure
- Chemical and pharmaceutical plants
- Crawl spaces and plant rooms
- Refurbishment projects where external access is limited
Getting Type C waterproofing right from the design phase offers major advantages, including:
- Non-invasive solution: No need for external excavation
- Reliable and maintainable: Easy access for inspection and servicing
- Reduces long-term risks: Prevents moisture-related damage and decay
- Compatible with monitoring systems: Adds peace of mind with alarms and backups
- Quick to install: Especially beneficial in retrofit projects
- Fully compliant: Meets BS 8102:2022 and other industry standards
- Flexible integration: Can be paired with Type A or B systems for enhanced protection
- British Standard: BS 8102:2022 – Type C (Drained Protection)
- NBS Clause: J40/290 – Flexible Sheet Tanking / Damp Proofing
- System Integration: Works with battery backups, dual pumps, and telemetry monitoring
Preventive waterproofing means perfection right down to the smallest detail
Concept design
RASCOR’s engineers analyze the waterproofed scheme in terms of structural design, groundwater/gravitational water conditions, and facility size.
Detail design
Full responsibility is assumed for key aspects of design, including the minimum shrinkage reinforcement, joint layout and concreting workmanship.
Site operations
Our engineers provide advice on and actively supervise the incorporation of the RASCOR White Tank waterproof concrete basement system.
Monitoring
Quality assurance is essential to the achievement of the agreed standards of workmanship. These activities are performed continuously up to acceptance/handover and the start of the defects liability period.