Most buildings extend below grade level. The below grade portions of the building enclose a variety of functional spaces ranging from fully occupied space to sensitive electrical vaults, water storage cisterns, storage rooms, and parking. This wide range of uses and tolerance for moisture within the space makes the design of the below grade waterproofing system challenging. For example, it is common for owners to accept some moisture ingress into below grade spaces in unoccupied areas such as parking. However, this is not the case for occupied spaces and water leakage through landscaped podium slabs and foundations walls into below grade spaces is one of the most common problems for building owners and managers, in addition to being a common source of construction litigation.

Unlike other building components that can be designed to be replaced several times within the service life of the building, many elements of the below grade systems cannot be cost effectively replaced and must therefore be designed and constructed to last the service life of the structure. Waterproofing in blind formed foundations walls is one example of a system that cannot typically be renewed or replaced during the service life of the structure. In all cases below grade systems are difficult to access and costly to repair or replace. For this reason durability of design and materials is mandatory with below grade enclosure systems. Quality assurance and control during the construction process is critical to the success of these systems.

Below grade enclosures typically comprise 3 main elements:

• Foundation Walls
• Floor Slabs
• Landscaped Plazas and Podium slabs

It is essential to understand the environmental and geotechnical loading on the below grade building enclosure and have a full understanding of the interior environment before selecting and designing the below grade waterproofing system. As with all elements of the building enclosure, the interfaces between the floors, walls and the roof, as well as all of the complex penetrations, must be integrated in order for the system to be functional. RDH’s extensive experience in maintaining, investigating, and repairing problems on existing below grade structures, coupled with our design and site experience constructing new buildings in marine environments below sea level, give us a unique understanding of the link between design and the ultimate long term performance of the below grade enclosure.

RDH was commissioned to undertake the Study of Poured-In-Place Concrete Wall Performance in Coastal British Columbia for the Canada Mortgage and Housing Corporation and Homeowner Protection Office. We have also produced a technical bulletin addressing concrete construction and waterproofing.