Designing waterproof systems
Particular attention should be paid to the specification of waterproofing systems - particularly for deep basements - relating to areas of high water table and in soils with aggressive chemicals. An appropriate specialist should be contacted for early advice and help on waterproofing design.
Good design and workmanship are primary factors in achieving waterproof construction. Key considerations are compatibility of waterproofing systems, sealing around joints and junctions of the waterproof membrane and, for integral structural waterproofing systems, attention to the construction joints.
Structural design may affect the choice of waterproofing and compatibility between the two is essential. For example, the stress and permissible crack width of a structure is controlled by reinforcement. In plain wall structures (i.e. not reinforced) the applied waterproof membrane needs to be appropriate to the anticipated movement of the structure, as the allowable movement or cracking may exceed the strain capacity of some waterproofing membranes. This is also a key consideration when refurbishing or extending basements, since movement between existing and new structures must also be anticipated.
Details and construction profiles should be simple, avoiding nibs and thickening of structure wherever possible to prevent complicated junctions. Adequate details must be provided for each junction and considered in three dimensions (3D) for thoroughness.
Although discontinuity with respect to waterproofing might be acceptable - subject to careful detailing and an appropriate assessment of risk - in practice this may not be allowed due to the need to manage radon, methane and other ground gases and contaminants.
Water stops are an essential part of the waterproofing design solution; for Type B protection used at the junction of structural panels, between walls and floors or along day-work joints for cast in situ concrete, the principle types can be classified as:
a) Passive sections e.g. PCV water bars, located outside or within the structure to obstruct water transmission.
b) Active strips or slurries (hydrophilic or crystallization) that react with water to prevent its further progression. These are set within the section of the structure, or post-injected.
c) Specialist sealing resin injected into pre-positioned permeable hoses or similar.
Further information is available from our guidance document Basements: Waterproofing