The benefits of a Type C (drainage) system

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Billy Shinners

A Type C (drainage) system is a water management system in which a cavity drain is utilised to control water once it has penetrated the structure of a building.

This type of system is designed to combat water ingress and can be used to grades 1-3, according to BS 8102:2009.

Installed utilising a high-density polyethylene internal drainage membrane, the system is loose laid in flooring applications and attached to the wall with surface plugs in vertical installations.

Water which has penetrated a structure is directed into the drainage system and collection sump before being discharged from the building via the pumps.

Key benefits

Type C (drainage) systems offer a host of benefits, starting firstly with installation. Easy to install with minimal preparation, they help to save time and money.

Their flexibility means they can accommodate minor movements within the structure too, without affecting the cavity drain system. Importantly, they do not put additional hydrostatic pressure on the location, meaning potential major reinforcement is not needed.

In addition, cavity drain systems provide a fail-safe in the event of other existing waterproofing measures failing.


When to use a Type C drainage system

Put simply, cavity drainage systems can be applied in most situations where there is some existing or potential water ingress that needs to be controlled.

This kind of drainage is often used in refurbishment as a primary waterproofing system where there is existing water ingress. When it comes to new builds, they are a secondary waterproofing system to provide a fail-safe. Additionally, these systems are regularly installed in instances where the existing structure cannot take further hydrostatic pressure due to the build up of water in the surrounding ground.

Useful in locations that are susceptible to water ingress, like old brick structures, Type C systems rely on the resistance of the structure itself but accommodate leakage and seepage, guiding the liquid to a suitable discharge point. This means they are commonly used in the walls and floors of basements and cellars.

Key considerations

Type C (drainage) systems require regular maintenance from specialist contractors in order to ensure they’re working effectively and to check that there has been no build up or blockage in the cavity. Clearing of contaminants, such as lime and silt, is vital as they have the potential to cause flooding.

The design of the system should consider maintenance such as access to sump/pumps and water channel. Backup pumps and alarms should be included in most systems, especially those in which consequences of failure are great.

Finally, designers need also to consider any risks associated with possible contaminated water entering the structure, as well as the location’s susceptibility to Radon.

A gravity-drained system may be an option for properties that are formed on sloping ground. This will remove the need for sumps and pumps, but will still require maintenance.

Sika has a range of materials for Type C systems, including pumps and membranes. To find out more about Sika products, call 0800 292 2572 or

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