A house sewer laid in undisturbed ground must be laid on what minimum thickness of approved material?

The correct answer is 4 inches because plumbing codes and standards often specify minimum material thicknesses to ensure durability and structural integrity. When a house sewer is laid within undisturbed ground, a thickness of 4 inches of approved material is typically required to provide adequate support, reduce the risk of collapse, and prevent external pressure on the sewer line. This ensures that the sewer can handle the weight of the soil above it and any potential environmental factors, such as movement in the soil or changes in moisture content.

Thicker materials may exceed the required specifications but are not often needed in undisturbed ground conditions unless other factors, such as soil instability, come into play. This standard helps maintain a safe and effective waste removal system within residential plumbing.