Known by several different names, but what are they ? and what do they do?
Their correct name is cavity drainage membrane. They consist of dimpled sheets which create a free-drainage layer between the wall / floor surface and the inner face of the membrane. The dimples allow the membrane to “stand-off” of the wall / floor so water can travel behind.
Cavity Drainage Membranes are not a form of “Tanking”. Tanking or in more recent “Barrier” waterproofing relates to systems which hold water out of basements – in the main they are fitted outside of the basement and not inside. Barrier systems are predominantly used for new-build projects …
It’s critical that accumulated water is removed from behind these membrane systems. They are not designed to stop water from entering the fabric of the building – they offer a drainage path for the water to travel towards a suitable exit point. In addition they offer a damp resistant / vapour impermeable inner skin to the basement rooms isolating them from damp walls.