When should waterproofing be applied to foundation walls?

Waterproofing should be applied to foundation walls when there is a possibility of hydrostatic pressure from the groundwater table. This is crucial because hydrostatic pressure can cause water to seep through cracks and joints in the foundation walls, leading to potential structural damage and moisture issues within the building. Proper waterproofing creates a barrier that helps prevent water intrusion under conditions where the water table may rise, ensuring the integrity and longevity of the foundation.

Applying waterproofing in such situations is a preventive measure. It is critical to identify areas where groundwater is present, especially in regions with a high water table or where soil conditions can promote water accumulation. Neglecting waterproofing in these circumstances can lead to significant problems, including mold growth, deterioration of structural materials, and unhealthy living conditions due to moisture.

The other choices imply scenarios where waterproofing may not be as necessary or effective. For example, applying waterproofing when hydrostatic pressure is not expected would not be beneficial, as the waterproofing is primarily a response to the likelihood of water infiltration. Additionally, waterproofing above grade does not address issues that may arise from groundwater, and excessive moisture alone does not necessarily indicate hydrostatic pressure concerns necessitating waterproofing.