Waterproofing of basements and other below ground structures

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The design of waterproofing systems shall be undertaken by a suitably qualified person and be appropriate for the specific performance required. Items to be taken into account include:

  1. waterproofing design
  2. risk-based design

Waterproofing design

Waterproofing systems should be designed by a waterproofing design specialist. Designers who have successfully completed the Certified Surveyor in Structural Waterproofing (CSSW) qualification available from the Property Care Association (PCA) are generally acceptable to NHBC. An alternative demonstration of competence may be acceptable, subject to successful review.

The waterproofing design specialist should be appointed in the early design stages to co-ordinate with other designers, including the engineer, and to ensure satisfactory integration of the waterproofing system.

Risk-based design

Waterproofing should be appropriate to the risk, and generally assume exposure to a full height of water during the design life of the building.

Combined systems should be used where:

  • a Grade 3 environment is needed, and
  • the wall retains more than 600mm.

Alternatively, where the builder has demonstrated that the water table is permanently below the underside of the lowest floor slab, a Type B structurally integral concrete system is acceptable without further protection from a combined system.

The following Types of waterproofing are acceptable where a Grade 2 environment is needed and more than 600mm of ground is retained:

  • Type A fully bonded barrier
  • Type B
  • Type C
  • a combined system.