Final answer:
Underground piping or tubing under a residential lawn is commonly buried at least 18 inches below grade to protect from damage and frost.
Step-by-step explanation:
The depth at which underground piping or tubing should be buried under a residential lawn depends on local building codes and the specific type of piping or tubing being installed. However, a common standard for the burial depth of residential underground piping is 18 inches below grade. This depth helps to protect the piping from potential damage due to surface activities or frost, ensuring the longevity and proper function of the piping system.