Below Grade Water Infiltration

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Water infiltrating into below grade spaces occurs when either surface water or ground water travels past or through a buildings’ foundation. Most foundations are constructed of concrete, masonry block or brick. Below grade foundations typically have either a moisture barrier or a waterproofing membrane installed on the foundations exterior face. These materials can and do deteriorate over time. When building foundations settle, cracks and other openings occur in the foundation structure. Water then infiltrates or travels from the exterior soil to the building’s interior spaces. All structures resting on or placed into the ground are subject to water intrusion.



There are two types of water proofing protection we will discuss here; they are positive water proofing protection and negative waterproofing.

Positive waterproofing systems are applications where the waterproofing systems and source of hydrostatic pressure are on the same side of the structural element, i.e. the exterior wall of a building foundation. Negative side waterproofing would be applied to an interior wall where the water source is located outside of the wall, such as a residential basement or below ground parking garage.

Negative waterproofing is the application of providing a waterproofing system on the interior surface of a grade slab, foundation or basement wall. For existing structures, the application of an interior waterproof system can be more practical than excavating the outside of the buildings’ foundation to install a positive waterproofing system. However, extreme storm conditions and/or poor foundation drainage conditions can cause excess negative side pressure to develop which can adversely affect performance by causing loss of adhesion and blistering of the waterproofing material. For this reason, positive side waterproofing provides the best performance alternative, however its’ installation cost on existing buildings far exceeds the cost of negative waterproofing applications. If negative side waterproofing is chosen, the degree of success will vary depending on the severity of the hydrostatic condition.


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