Waterproofing concept and considerations

To define the appropriate waterproofing strategy and type of system for a specific project, it is important to consider not only the ground conditions but also the project requirements.

The British Standard BS 8102:2009 describes different levels of watertightness required for the end use of a structure.

For waterproofing structures below ground, BS 8102:2009 outlines three different waterproofing methods, the choice of which should take all of the relevant project requirements into consideration.

  • Type A waterproofing, also known as tanking, is an externally or internally applied barrier system applied to the walls and floors of the structure that can withstand ground water from entering the building under pressure.
  • Type B waterproofing is an inbuilt characteristic of the actual structure by adding waterproofing additives to the concrete used to form the floors and walls of the structure.
  • Type C waterproofing is essentially a set of dimpled membranes called Cavity Drain Membrane (CDM) installed externally or internally to the walls and floors of the structure. A type C system does not aim to prevent water coming into the structure but instead manages it and diverts it into either a pumping chamber or external land drain.

Grade 1

Basic utility

Some seepage and damp areas tolerable*

– Underground car parks
– Plant rooms
– Workshops

* Dependent on use

Additional requirements

(formerly Grade 4)

As Grade 3, plus consideration of the internal environment required

– Air conditioning
– Ventilation
– Radon and methane protection
– Residential areas
– Computer rooms
– Archives
– Special purpose facilities and areas

Grade 2

Better utility

No water penetration, ventilation may be required

– Underground car parks
– Storage areas
– Workshops
– Electrical plant rooms

Grade 3


No water penetration, totally dry environment

– Ventilated residential units and offices
– Restaurants and commercial areas
– Leisure facilities