The ground immediately adjacent to the foundation must be sloped away from the building at a minimum slope of what?

The ground immediately adjacent to the foundation should be sloped away from the building at a minimum slope of 1:20. This means that for every 20 units of horizontal distance, the ground should drop at least 1 unit vertically. This slope helps ensure effective drainage away from the foundation, reducing the risk of water pooling around the base of the building.

Proper drainage is crucial in preventing moisture-related issues such as erosion, seepage, and other water damage, which can compromise the structural integrity of the foundation over time. A slope of 1:20 is seen as practical and sufficient to encourage water runoff away from the foundation, thereby minimizing potential damage.

Greater slopes, such as those represented in the other choices, may be excessive for standard drainage needs and could complicate landscaping and accessibility around the building. In practice, a more gradual slope like 1:20 strikes a balance between effective drainage and manageable terrain for landscaping and building usability.