When is waterproofing required over damp-proofing for foundations?

Waterproofing is specifically required over damp-proofing for foundations in situations where hydrostatic pressure exists. Hydrostatic pressure refers to the pressure exerted by water in the soil surrounding a foundation, which can significantly impact the integrity of the structure. When there is a high level of moisture in the ground, especially in areas with a high water table or poor drainage, the pressure from the water can lead to water infiltration if only damp-proofing is used.

Damp-proofing is designed to resist moisture, but it is not impermeable to water under pressure. Therefore, in conditions where hydrostatic pressure is a factor, waterproofing is necessary to provide an effective barrier against water that could otherwise seep into the foundation walls and cause damage over time. This distinction is essential for ensuring long-term durability and preventing issues related to moisture, such as mold growth or structural deterioration.

The other options do not accurately represent the conditions that necessitate waterproofing. While heavy rainfall can increase moisture levels, it does not always correlate with hydrostatic pressure; foundations may still manage without waterproofing depending on drainage and soil conditions. Similarly, waterproofing is not universally required for all foundation applications or only applicable to commercial buildings, as residential structures with similar risks also require proper waterproofing