The first question that an architect will have to answer is if waterproofing is required on the building that they are designing. This can be a complex question and the answer could have significant ramifications over the life span of the structure. Economic and code requirements could also weigh heavily in the decision process. Waterproofing may be included for peace of mind, as this is the one component of the building that it may be best to caution on the side of err.
Once there is determination that waterproofing is required, the designer faces the equally daunting question of determining whether dampproofing or waterproofing is required and where they should be applied. In order to correctly decipher where to use waterproofing and dampproofing the designer should be familiar with these types of materials and the basic waterproofing design elements of each.
Dampproofing is a system designed merely to resist the flow of moisture in a gaseous state. It can only be used in below-grade walls that are not subjected to hydrostatic pressure. These types of systems resist the flow of water vapor through a building component. They are most commonly used to prevent or reduce migration of water by diffusion. The most common form of dampproofing material is bituminous (asphalt) coating, which is either solvent-based (cut-back asphalt) or emulsion. These coatings are applied in one or more applications with a brush, spray, or trowel. Reinforcements are rarely applied in these systems. If reinforcements are used they typically consist of woven jukes or cotton fabrics that are specially applied over substrate cracks or openings.
Waterproofing systems are designed to resist hydrostatic pressure that is extended by moisture in a liquid state. Waterproofing systems typically use reinforcement membranes that can be adhered to the substrate in a variety of application methods. Typical application methods include hot application with heated asphalt, cold applications with solvent based adhesives, torch applications or self adhered membrane sheets.
The decision to use waterproofing or dampproofing systems can be determined by three criteria. First, if hydrostatic pressure is present, a waterproofing system is required. A waterproofing system is also required for framed slab constructions. For retaining walls or slabs-on-grade the question is whether a slight leak risk is acceptable. If the answer is yes, then dampproofing may be considered. If the answer is no, then waterproofing is required.
There are two basic configurations of below-grade components that require dampproofing or waterproofing. The first is a “box” configuration that consists of a structural slab on top, foundation walls on the sides and a slab-on-ground at the bottom. The other type of configuration is an “L-shape” configuration, which consists of a foundation and a slab-on-ground with no structural slab.
The type of waterproofing treatment applied at these components is based on the three criteria that are identified above and the following three basic rules of waterproofing design:
- You must waterproof the structural slab because it will be subjected to hydrostatic pressure from surface runoff.
- If you waterproof the slab-on-ground, you must waterproof the foundation wall – particularly if there is a fluctuating water table.
- You must either dampproof or waterproof both the foundation wall and the slab-on-ground
- Waterproofed structural slab, plus dampproofed wall and slab-on-ground
- Waterproofed structural slabs, walls, and slab-on-ground
- Waterproofed structural slab and walls, plus dampproofed slab-on-ground
- Dampproofed foundation wall and slab-on-ground
- Waterproofed wall and slab-on-ground
- Waterproofed wall, dampproofed slab-on-ground