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 it from water infiltration to avoid cracking and other damage that would have subsequent repercussions on the building.
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 covert 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 the context 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).
Waterproofing, alternatively, refers to treating a surface to prevent the passage of water under hydrostatic conditions.
Note that dampproofing can’t be used if there’s a significant risk of hydrostatic conditions forming.
Positive-Side Waterproofing vs Negative-Side Waterproofing
There are a few ways to go about below-grade waterproofing design. First, there is positive-side waterproofing, which consists of installing a waterproofing membrane or 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 and tends to be the most successful, since it keeps water out and actually benefits from the external water pressure forcing it to work. It also allows the design team to inspect all lap joints and defects with full visibility.
The biggest drawback, however, is that once areas have been filled in with earth around the foundation, post-backfill inspection is not possible. If leaks occur due to building movement or faulty installation, repairs can only be made through excavation or interior retrofits.
There is one additional form of below-grade waterproofing to know as well: negative-side waterproofing. As you might guess from the name, negative-side waterproofing 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. It is primarily used for water-holding purposes (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 the installation for repairs or upgrades.
Water Management and Protection
Keeping water out is one challenge; managing water and protecting newly installed below-grade waterproofing assemblies is another. Therefore, we should also install protective layers, drainage layers and waterstops.
Protective layers, as their name implies, 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 or asphaltic boards. In some cases, layers serve dual purposes, such as insulation and drainage.
Drainage layers, alternatively, assist in the relief of hydrostatic head pressure and prolong the membrane life. Proper design means having the least possible amount of water reaching 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 prevent possible damage from backfill operations, or a drainage solution to direct the water away from the waterproofing membrane. Some drainage solutions can protect both the membrane and manage water.
Waterstops provide a final level of protection for the building, existing within concrete sections, especially joints. These premanufactured joint seals are often comprised of PVC or chloroprene rubber that must be fused together, bentonite clay that expands when wet, or hydrophobic injectable expanding grouts.
Key to Success
A good initial design begins with good communication between all team members. All team members involved need to be on the same page before and during the project to ensure a successful outcome. Waterproofing needs to be considered at the front end of any building construction project—in the design phase of a project. Designers and architects should consult with waterproofing manufacturers and contractors during the design phase to ensure that all requirements are fulfilled. Many major problems with projects can be traced back to parties failing to talk with one another or pre-construction meetings not being scheduled properly, so take special care to avoid potential oversights early on. When selecting a system design and the materials that will be used for a project, there are a number of questions worth asking yourself in order to make an informed decision.
Consider, for instance, the following:
- What are the site conditions?
- What are the soil conditions?
- What temperature limitations exist?
- What is the hydrostatic pressure at the location?
- What sort of drainage is found on site?
- What will construction sequencing be?
- Are all of the applicable materials compatible?
- What are the code requirements?
- How much is the building expected to move?
- What will be the primary function of the building?
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.