Engineering and Construction

The main structural design and construction details to prevent moisture migration through basement walls is a drainage system at the base of the wall to prevent the build-up of hydrostatic water pressure and a waterproofing system applied to the exterior wall surface. Such a system for basement walls is shown in Fig. 11.24. A perforated drain is installed at the bottom of the basement wall footing. Open graded gravel, wrapped in a geofabric, is used to convey water down to the perforated drain. The drain outlet could be tied to a storm drain system.

The waterproofing system frequently consists of a high strength membrane, a primer for wall preparation, liquid membrane for difficult to reach areas, and mastic to seal holes in the wall. The primer is used to prepare the concrete wall surface for the initial application of the membrane and to provide long-term adhesion of the membrane. A protection board is commonly placed on top of the waterproofing membrane to protect it from damage during compaction of the backfill soil. Self-adhering waterproofing systems have been developed to make the membrane easier and quicker to install. For example, Fig. 11.25 shows a self-adhering waterproofing system that has been installed to the back side of a basement wall. In Fig. 11.25, the waterproofing system is located on the right side of the photograph and the perforated drain is visible in the center of the photograph.