Structural water proofing using a cavity drain membrane

Structural waterproofing

A brief overview of Structural Waterproofing of wall and floors

Structural water proofing is the name for systems that damp proof below ground structures. In existing properties structural waterproofing is carried out from the inner wall surface.  Often using a Cavity Drain Membrane as the older wall/floor masonry may be in a weakened condition and it will not put additional load on the floor and wall structure, sometimes a combination of type A & C may be used.  Within its design limits, a cavity drain membrane will manage the failure of the buildings ability to resist groundwater penetration.  For instance, I have found in the Edinburgh new town area the cellars floors are often well-drained and have no water table issues.  This is due to their construction and the geology.  A CDM system is commonly used to control the water percolating down through the pavement and porous ground above the under-pavement cellar.

New construction sites have a diverse set of waterproofing problems compared with an existing building which has a history of resisting water.  In a new building, you are excavating underground (and into the unknown), and the new site has a lack of site water history.  This is why more investigation is needed.  This starts with a desk study followed by a site inspection.  The research helps in select materials and create a suitable specification, which needs to address any ground contamination due to past usage of the land, ground gases, i.e. Radon and potential flooding of the area due to location.

This is why a combination of Type A and B waterproofing system is preferred, this is applied to the new structure externally, or as part of the structure and both may require a suitable maintainable land drain installed to prevent water building up on the outside and finding a defect.  By combining these, you may create a tanked construction which is able to resist water penetration.

It is important that a suitably trained person advises a client.


Type A:  This system relies on a coating/membrane being applied to the wall/floor to make the structure resistant to the passage of groundwater. A manageable land drain should be installed to prevent water from finding a defect in an external coating or membrane and diverted to a suitable soakaway.  Groundwater should not be discharged into a vested sewer.

Type B:  Is the best form of the three types as the (often waterproof concrete) wall/floor construction structure is built to resistant to groundwater penetration.

Structural water proofing using cavity drain membrane
basement area

Type C:  Is formed out of a studded plastic membrane which manages the water entering the building. This is often used for repairing an area (this is not a tanking). It can be combined with a Type A or B to make them more repairable.

Groundwater should not be discharged into a vested sewer, but surface water can be.

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