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By: Anthony Ngadimin

Below-grade water infiltration may render an interior space uninhabitable but also cause damage to structural components through steel reinforcement corrosion, concrete spalling, and structural cracking.

Below-grade areas may be exposed to conditions that are more severe than above-grade areas, either by constant hydrostatic pressure from groundwater tables or through cyclic water tables during periods of heavy rainfall.  

Most below-grade waterproofing is not easily accessible once construction has been completed. Therefore, it is important to get it done correctly from the start. When working on water infiltration issues on an existing building, it is important to understand the cause of water infiltration before employing solutions to address them.

Building Owners and Property Managers are often faced with complications, such as budget and access when dealing with below-grade water leaks. It is important to have a basic understanding of the systems that are commercially available, as well as the methods by which they are employed to ensure that the correct solution is employed on their particular project.  

Types and Methods of Installing Below-Grade Waterproofing

There are various waterproofing systems that are commercially available on the market, namely: 

  1. Liquid-based systems:
    • Hot-liquid applied systems
    • Cold-liquid applied systems
    • Single and multicomponent systems
  2. Sheet-systems:
    • Modified bitumen sheets
    • Elastomeric sheets
    • Thermoplastic sheets
  3. Mineral-based systems:
    • Bentonite clay
    • Crystalline/cementitious systems 

 There are three main ways by which waterproofing could be installed. A positive-side application means that the waterproofing is installed between the substrate you are protecting and the source of water. This type of application is also commonly termed exterior side waterproofing, as the waterproofing material is installed on the outside of the building.  

Negative-side waterproofing keeps water from entering an occupied space and is installed on the interior side of the building. However, this type does not prevent the water from entering the substrate.

 In new construction, there is a third type of waterproofing called blind-side waterproofing, whereby waterproofing is installed on the soil retention wall rather than the structure’s new wall. These systems could still be considered positive-side waterproofing since they are applied on the outside of the building. 


New Construction

The best-case scenario is that a building is designed adequately from the initial stage of construction. They say the devil is in the details and it cannot be truer in the case of below-grade waterproofing. There are various factors that must be considered in the design development stage that could avoid costly issues in the future. For example:

  • What is the level of the water table on-site?
  • What other construction materials are used, and are they compatible with each other?
  • Are terminations detailed adequately?
  • Is the substrate prepared properly?

Even when it is designed and drawn correctly on paper, many things could go wrong on-site. We always recommend working with Contractors that are approved by the material manufacturer, as they understand how to install specific details. It might also be beneficial to involve a consultant during the construction phase to inspect the waterproofing at critical points before any backfilling occurs and the waterproofing becomes inaccessible. 


Existing Construction

In existing construction, our ability to access the positive side or exterior of the building may be limited by the cost of practical reasons. Imagine trying to access an underground basement parking garage 6 stories below grade; it’s not impossible, but the costs would be astronomical! Thereby, negative-side waterproofing is typically employed in existing structures. This comes with its own set of challenges since interior spaces are often occupied in existing buildings.



There are various types of waterproofing systems available on the market. The selection of waterproofing materials and method of installation is dictated by multiple factors such as accessibility and budget. It is critical to install waterproofing right the first time, as rectifying waterproofing issues in existing construction can be costly and challenging. 

Sullivan Engineering provides end-to-end construction services from new construction to existing construction. We have experience working in new building commissioning whereby we work alongside Architects and the construction team in reviewing design details and specifications, assisting in material selection, and performing quality assurance inspections to identify workmanship issues on-site.

Our team is also experienced in existing construction projects whereby we work together with building owners in developing a remediation plan that suits any project budget.

Contact us to learn more.

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About Sullivan Engineering, A Rimkus Company

Sullivan Engineering provides high-quality building envelope restoration and compliance solutions.

We partner with facilities managers and account executives to provide technical expertise and project management for building envelope restoration, compliance, and maintenance.

Our solutions reduce the overall building life cycle maintenance costs by creating long-lasting, high-quality work for years to come.


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