It’s not uncommon for waterproofing to take a backseat when developing plans and specifications for a building. Yet when it comes to protecting a building’s foundation from the impacts of water infiltration, there are good reasons why waterproofing needs to stay top of mind.
“The foundation ensures building loads are supported and distributed. It is therefore critical to protect them from water infiltration to avoid cracking and other damage that would have subsequent repercussions on the building,” Catherine Lavoie Canuel, Product Manager of Building Envelope with Soprema.
Certainly, while the more visible elements of a building tend to receive the most attention, it’s often the unseen components that can have the greatest impact on building performance and sustainability.
Are you hoping to keep those unseen risks at bay? Here are a few things to know about protecting your foundation.
Waterproofing vs. dampproofing
There are essential differences between waterproofing and dampproofing. In terms of below-grade protection, dampproofing refers to treating a surface to resist the passage of moisture in the absence of hydrostatic conditions (e.g., if your surface is above the water table). Essentially, it acts only as a barrier against moisture and provides no protection in case of water accumulation when drainage at the bottom of the foundation walls doesn’t work properly.
Waterproofing, alternatively, refers to treating a surface to prevent the passage of water under hydrostatic conditions. It’s the solution for all below-grade conditions that are or might be exposed to hydrostatic pressure (e.g., with high water-table levels) or in flood-prone areas.
Note that dampproofing is not a substitute for waterproofing if there’s a realistic chance of hydrostatic conditions forming.
Installing waterproofing membranes
There are a few ways to approach a below-grade waterproofing design. First, there is positive-side waterproofing, which consists of installing a waterproofing membrane/layer between the substrate you are protecting and the source of water. This type of application is commonly referred to as exterior side waterproofing, as the waterproofing materials are applied to the outside of the building.
Positive-side waterproofing is generally seen as the least problematic option to pursue. It tends to be the most successful since it keeps water out and is benefited by the external water pressure that is forcing it to work. This method also allows the design team to inspect all lap joints and defects with full visibility. “The excellent elongation properties of the membranes provide sealing and protection for the foundation as a whole in the event of new cracks,” explains Lavoie Canuel, noting, “The biggest drawback, however, is that once areas have been filled in with soil around the foundation, post-backfill inspection is not possible. If leaks occur due to building movement or faulty installation, repairs can only be made via excavation or interior retrofits.”
Negative-side waterproofing, as the name implies, protects the surface opposite the side of applied hydrostatic pressure (e.g., the inside of a basement wall). Negative-side waterproofing keeps water from entering an occupied space and is applied to what is known as the dry face. Negative-side waterproofing is primarily used for water-holding purposes (e.g., preventing water from entering a space), but it does not prevent the water from entering the substrate (wall). The main advantage of negative-side waterproofing is that it is accessible after installation for repairs or updates.
Managing water around the foundation
Keeping water out is one thing; managing water and protecting newly installed below-grade waterproofing assemblies is another altogether. Therefore, it is recommended to install protective layers, drainage layers, and water stops. Specifically:
- Protective layers protect below-grade membranes from damage. This damage can either occur from backfill or consecutive trades. Depending on the membrane, common materials used in protective layers include insulation, asphaltic boards, or an additional layer of HDPE. In some cases, layers serve dual purposes, such as insulation and drainage layers.
- Drainage layers help relieve hydrostatic head pressure and prolong membrane life. Proper design means having the least possible amount of water reaches the membrane, and water management is highly recommended in all below-grade assemblies. These panels are typically impact-resistant, dimpled plastic attached to a woven geotextile fabric, and they channel water away from the membrane. Almost all below-grade waterproofing projects will have either a protection layer (board) to protect against possible damage from backfill operations or a drainage solution to manage the water away from the waterproofing membrane. Some drainage solutions can protect both the membrane and manage the water.
- Waterstops provide a final level of protection for the building. They exist within concrete sections, especially joints. It is best to promote the evacuation of water near the foundation walls. In this case, a gravity drainage system is recommended. In some cases, however, it is not possible to evacuate water by gravity, so a tanking system should be considered.
The science behind below-grade waterproofing
There are three major environmental forces that come into play when avoiding unwanted moisture infiltration: hydrostatic pressure, capillary action, and the water table.
Hydrostatic pressure is pressure exerted by a stationary liquid in all directions against adjacent surfaces. Water exerts 0.43 psi of pressure for every foot of water present, and this pressure increases with depth and seasonal rainfall levels. Resulting from water-saturated soil, this pressure can occur against vertical foundation walls as well as under-the-floor slabs, putting additional loads on the structural elements and forcing water into any crack or imperfection in the structure, thereby making waterproofing more difficulty.
Capillary action (aka “capillarity,” “capillary motion,” or “wicking”) refers to the ability of water to flow in narrow spaces without the assistance of—and in the opposite direction of—gravity. Hydrostatic pressure can force the migration of water through any punctures or gaps in the membrane, ultimately leading to water infiltration inside the building.
Lastly, construction activity around a building can affect the water table; that is, the level below which the ground becomes saturated with water. As a result, the hydrostatic pressure exerted on a building can change, subsequently affecting the capillary action within your building materials.
Waterproofing comes with many considerations, each of which needs to be examined carefully to protect critical components and maintain the health of a building. The complexities can be overwhelming, but that’s where having the right expertise and materials can seal the deal.
For more information, visit Soprema.ca.
