1. Design

1.1 There are 2 different categories of in ground works and 4 different scenarios/risk categories (in order of importance – 1= most risk, 4 = least risk);

1.1.1 WATER RETAINING STRUCTURES

a. Waterproofing of ground & water retention walls – e.g basements, lift pits etc below the water table, water tanks etc.

1.1.2 INGROUND AREAS

a. Waterproofing of ground retention walls where there is HABITABLE building space on the other side e.g underground offices or retail areas –“lower ground” areas – buildings on steep hills steeped against the hill – minor hydrostatic loads
b. Waterproofing of ground retention walls where there is a NON HABITABLE building space on the other side e.g underground car parks (may be a “dry” or “wet” basement car park) – minor hydrostatic loads
c. Waterproofing of ground retention walls where there is no building space on the opposite side – e.g a landscape retaining walls (looking to protect finishes on the wall and seepage only) – minor hydrostatic loads

1.2 The first step in designing the waterproofing system is to determine the standing water level. This is the level that the water table NORMALLY sits at.

1.3 Bear in mind that at times of prolonged wet weather the table will be higher than at times of prolonged drought and requires some level of judgement.

1.4 If the building is BELOW the standing water level – then the area is a WATER RETAINING STRUTURE.

1.5 This means the membrane is underwater all the time. So - paint on acrylic membranes, or even a paint on “blackjack” just won’t do the job. They would not be FIT FOR PURPOSE.

1.6 Primary consideration for this work is the protection of the structure itself – the waterproofing system needs to protect the structure from aggressive contaminants in the water- acid sulphates, salt water etc. This is known as “brackish” water and will rapidly deteriorate a structure by rusting reinforcement, attacking membranes, and waterstop seals that are not design to resist this type of water.

1.7 If the building is ABOVE the standing water level then it will be an in ground application. The type of membrane is then selected based on a cost versus risk. There is little point spending considerable extra cost using a water retaining structure equivalent system on a basement in a dry environment where water ingress is very limited.

1.8 A planter box built hard against a residential unit wall (not allowed in this policy by the way) is likely to deserve more attention/consideration than a planter box in an on grade car park.

1.9 In summary there are waterproofing systems/membranes best suited to each application