A Type C System isn't classified as a hydrostatic barrier but will provide protection by means of water management. The principal determining factor with Type C is a formed Cavity that enables water to run through the system and is directed to collection channels. Collection channels deliver the water to a discharge destination. In order for this to be achieved, a cavity drain membrane(CDM) is used with drainage pipes directing to a sump and pump system to manage the disposal of the collected water. Crucially, the pumped water is discharged into suitable drainage capable of managing large quantities of water.

The British standard (BS8102:2009) deems that combined protection should be considered where the project is classified as high risk, the consequences of falling to achieve the intended internal environment are too high additional vapour checks are necessary for a system where unacceptable water vapour transmission can occur