How Deep to Install Sprinkler Pipes

Pipe Size

• The physical size of your supply pipe will determine, in part, how deep to set your trenching machine. Most pipes for residential sprinklers are 1 inch in diameter. This means the trench should be at least 1 inch wide, to accommodate the width of the pipe. You should add at least 2 inches to the size of your pipe to calculate the minimum depth. For a 1-inch pipe, the total depth shouldn't be less than 3 inches. But this number must be added to other measurements.

Sprinkler Size

• In addition to pipe size, you must measure the size of your sprinkler heads. Sprinklers come in standard sizes of 2, 4, 6, 8 and 12 inches long. Add the length of the sprinkler to the size of the pipe to get a preliminary idea of how deep to set the trenching machine. A 6-inch sprinkler on a 1-inch pipe, for example, requires a trench depth of at least 9 inches at this point (6 inches for the sprinkler head plus 3 inches for the 1-inch pipe).

Riser Size

• All sprinklers sit on plastic risers. These devices connect the sprinkler to the supply line below. Risers come in a variety of sizes, including customizable sizes. In most cases, a riser will sit flush between the supply line and the sprinklers, meaning no additional depth is needed to accommodate the riser. However, if your terrain calls for using a taller riser, or you want to use a small sprinkler, you must add the length of the riser to the total depth of the trench. A 3-inch riser, for example, would add 3 inches of depth to the trench.

Surface Cover

• Consider the type of surface cover when digging a trench. Plants such as grass grow their roots straight down. Digging a trench too shallow can inhibit the growth of grass along the pipe path. Make sure your pipes are at least 5 inches deep to avoid stalling grass growth. If the surface material is rock or other substrate, your sprinkler depth doesn't matter. In those areas, sprinkler pipes that don't immediately connect to sprinkler heads can be installed at shallow depths of about 3 inches.