Below-Grade Waterproofing: What It Is and Why You Need It

Below-Grade Waterproofing: What It Is and Why You Need It


Below Grade Waterproofing Barrier

Two of the most common threats to the structural integrity and performance of the building envelope are below-grade uncontrolled water and moisture intrusion. There are three conditions needed to move water through the building envelope:

  • A water source,
  • An opening or path for the water to follow, and
  • A force to drive water through the opening.

If a building’s foundation is not properly waterproofed, pooled water can cause erosion and subsequently lead to cracks. Water in the soil surrounding a building creates pressure on its foundation. If this water isn’t funneled away from the structure’s foundation, it can cause cracks and leaks that lead to water penetration and could lead to failure of the building’s structural integrity.


Protect the Integrity of the Building Envelope

The foundation of a building is critical to the integrity of the structure, so it is important that it remains free from water intrusion and damage. Below-grade walls are typically constructed of concrete and/or concrete masonry units (CMU), both of which are porous and can crack from building settling or curing of materials. Applying a barrier between the foundation and surrounding earth can stop water as well as other harmful soil contaminants from entering the building.


Below-Grade Waterproofing

Below-grade waterproofing is the process of applying coatings and membranes to the below-grade walls of a building’s foundation. ASTM Standard D7832 states that “a waterproofing membrane should maintain its watertight integrity for the life of the building in a continuously or intermittently moist environment” and “should resist chemicals that can harm the membrane and root growth” [1].

Types of Waterproofing Membranes

There are two main types of below-grade waterproofing membrane systems:


  • Prefabricated: Bentonite, modified bitumen, elastomeric sheets or thermoplastic membrane
  • Fluid-Applied: Cold liquid-applied or hot-liquid applied, or single components membrane systems

Application of Waterproofing Membranes

Once you have determined the type of waterproofing membrane that best fits your structure, there are three common application processes:


  • Positive-Side: Applied after the wall is built and requires access to the outside face of the wall
  • Blind-Side: Pre-applied prior to foundation wall construction
  • Negative-Side: Applied to the interior side of a building, usually when positive-side or blind-side application processes aren’t possible

Regardless of the type of membrane or application process chosen, below-grade waterproofing is a practical solution that will keep your building safe and free of moisture and potential contaminants.

Make Your Investment Last

If you have concerns about water infiltration in your building envelope, Technical Assurance can partner with you to alleviate them. With over 30 years of experience, we specialize in structural analysis, hardscape remediation, as well as above-grade and below-grade waterproofing. While below-grade waterproofing may be an upfront cost, ultimately it will lower your total cost of ownership in the long run. Combined with a structural water mitigation strategy, your investment should be protected well into the future.

Contact Us Today!

Technical Assurance can perform a building envelope assessment to investigate water intrusion concerns and give you an actionable plan to ensure your investment lasts. Contact us today for a consultation.