How Deep Should an Underground Sprinkler Pipe Be?

Underground sprinkler system pipes are buried to not only protect water in them from freezing and bursting the pipes, but more importantly, to keep them from being damaged by machine or manual digging. In burying the pipes of your sprinkler system, you will need to know how deep they should be buried.

Plastic Mainliine Pipes

Plastic mainline pipe trenches should be a minimum of 18 inches from the top soil surface to the top pipe surface. This means that if you are burying a mainline pipe that is 1½ inches in diameter, the trench will need to be 20 inches deep. A mainline pipe is one that is installed between a water source and a control valve, a pipe that is constantly filled with water under pressure.

Plastic Lateral Pipes

Lateral pipes used in residential sprinkler systems should be about 10 inches deep. If sprinkler pipe trenches are dug by a trench digger, these trenches should be dug 2 inches deeper. Trenching machines almost always leave about 2 inches of loose dirt in the bottom of the trench they've dug. So, your choices will be to either remove this 2 inches of loose dirt by hand or have the machine dig 2 inches deeper. Then, you can leave the loose dirt in the trench.