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Below-Grade Waterproofing Systems 101: Commercial Builds

14 minutes read

Below-Grade Waterproofing Systems 101 for Commercial Buildings

Unlike residential waterproofing, commercial moisture issues affect more than one family.

When building or maintaining a commercial property, waterproofing should be one of your top priorities. Without the proper seals and barriers, your hard work could sustain damage that leads to larger (and grosser) problems like dry rot and mold.

But where do you start? Perhaps at the bottom. Below-grade waterproofing systems give your build a solid foundation for years of beauty and functionality. Not only will you avoid the property owner screaming at you about repair costs, you’ll also ensure the space remains open – and making money.

We’re here to help you navigate the world of waterproofing a commercial building so your work holds up over time.

What is Below-Grade Commercial Waterproofing?

While weatherproofing your entire commercial build is essential, it’s important to start with below-grade foundation waterproofing. This involves treating a surface or structure to prevent the passage of water under hydrostatic pressure.

Below-grade waterproofing is applied where the underground comes into contact with a structure. A few examples include:

  • Horizontal concrete blocks
  • Exterior walls
  • Plaza decks

There's a range of moisture-proofing products that address any use case you could think of; we'll get to them in a bit.

Benefits of Below Grade Waterproofing

By using the right sealants and membranes, you can protect your commercial build from waterproofing failure, structural weakening, and human health hazards.

As you can imagine, without below-grade waterproofing, the foundation of a commercial or industrial structure is prone to moisture damage. This can impact its integrity to the point where the only option is restoring the building. Deterring water damage means reducing the amount needed to make any future repairs, are often incredibly costly for the owner.

Dry rot, mold, and the other negative effects of leaks can be difficult to see. The longer they exist, the more it'll cost to make repairs. Commercial waterproofing not only protects facilities from the immediate cost of fixing leaks; it also saves property owners money in the long run.

Preventative vs. Reactive Waterproofing

Commercial waterproofing can be either preventative or reactive.

Proactive measures usually happen during a build since waterproofing the foundation is a natural step in the construction process. During this phase, try to expand your understanding of the job site itself. A geotechnical report, for example, can help you understand the soil and the waterproofing solutions that will work best for the application.

Reactive measures are probably inevitable too; even the strongest below-grade waterproofing system can leak or wear down over time. Concrete-repair products and other restorative solutions can patch the problem and strengthen the area once again. Of course, the more proactive measures you set in place, the fewer "uh-oh" moments the owner will have later.

Waterproofing Methods in Construction

Because commercial waterproofing systems are so vital to safety and longevity, there are a slew of products and materials dedicated to below-grade use. (Some can be used both above and below ground.)

Positive vs. Negative/BlindSide Waterproofing

The use of positive vs. negative (blindside) waterproofing almost entirely depends on your crew's access.

Positive-side waterproofing is your go-to when you can easily access below-ground elements. Examples include vapor barriers, fluid-applied membranes, and even hot-applied bitumen systems. Don't forget to tack on some protection boards or insulation layers to keep that waterproofing layer safe when backfilling.

Negative-side waterproofing comes in handy when you can't reach the below-ground area. Negative-side goes on the interior surface after it's already been built, acting as a last line of defense. This method doesn't stop water from entering the substrate, but it can direct ingress to a drainage system.

Blindside waterproofing is also for tough-to-access areas, but you apply it before the structural slabs are in place. Rather than internal, it's location is between the ground and the underside of the slabs.

Vertical vs. Horizontal Waterproofing

As you've surely figured out, these strategies differ by the orientation of the surface you're protecting.

Vertical waterproofing create resistant barriers for wall envelopes below the ground. Fluid-applied membranes and other products seal off groundwater or rainwater that may otherwise seep in from the sides. Next time you're knee-deep in a below-grade project, don't overlook the vertical aspects!

Horizontal waterproofing is common in basements and tunnels. It's usually best to place it beneath the slab, either before or after you install the slab. Depending on your use case, horizontal waterproofing can be a standalone system or work in tandem with vertical waterproofing products.

Types of Waterproofing Products

Understanding which products to use is just as important as the waterproofing process itself. Common options for commercial spaces include:

  • Fluid-applied membranes – These hot- or cold-applied liquids are based on water, urethane, solvents, or cement. They're easy to spread with a roller, brush, or sprayer for a uniform finish, but drying takes some time.

  • Sheet-applied membranes – These include modified bitumen, bentonite, elastomeric, and thermoplastic sheets that seal off water in every direction and prevent lateral migration. These products are self-adhering and can be pre- or post-applied, making them a versatile building envelope material.

  • Coating – Primers can seal concrete and prepare a surface for application of asphalt or membranes. One newer product to watch is PUMA coating, a system rated for immersion and chemical exposure that's possible to cold-apply to finished flooring.

  • Drainage – Composite mats and fabrics deflect water and relieve hydrostatic pressure in vertical and/or horizontal systems. When choosing one, strength and flow rate are important criteria, but don't forget to consider the sturdiness of your below-grade waterproofing membrane.

  • Flashings – This reinforcing, self-adhered product – often made of rubberized asphalt – is installed inside walls. It collects water penetrating cracks in the exterior and directs it back outside.


Long-Term Success With Below-Grade Waterproofing Systems

The sooner you account for moisture in a new or restorative commercial project, the higher your odds for success. By choosing waterproofing materials and methods that prevent rotting and mold, your build will keep structural and aesthetic value for years to come.

No matter the solution you need, there are plenty of below-grade waterproofing products available to get the job done. From blind-side and cold-applied membranes to hot rubberized asphalt and self-adhered flashings, what works best for your commercial build comes down to:

  • The structure
  • Its surroundings
  • Any existing waterproofing system

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