What depth of gravel or sand is required under a house sewer laid in undisturbed ground?

The requirement for a 4-inch depth of gravel or sand under a house sewer laid in undisturbed ground is based on standards that aim to provide proper support and drainage for sewer pipes. This depth ensures that the soil has enough material to effectively distribute weight and prevent settling or shifting of the sewer lines, which could lead to blockages or breaks in the pipe.

Gravel or sand serves several important functions: it allows water to drain freely away from the pipe, reducing the chances of erosion around the pipe, and it also minimizes the risk of pipe damage due to pressure from the surrounding soil. The depth of 4 inches is typically deemed sufficient for effectively supporting the pipe and promoting good drainage characteristics.

Comparatively, options suggesting shallower depths would not provide the necessary support and drainage, while recommending deeper depths could be excessive for the requirements of most residential sewer installations, both of which could lead to unnecessary costs or complications in the installation process. Thus, the standard practice of using a 4-inch layer of gravel or sand under sewer pipes in undisturbed ground is well-supported by plumbing codes and practices.