Sprinkler lines should be buried below the grass roots, and deep enough the sprinkler heads sit flush with the soil surface or slightly above grade. The depth varies depending on factors but typically ranges from eight to 12 inches.

A key aspect of installing a new sprinkler system is to bury the supply line at the correct depth. Generally, lines are buried beneath the lawn’s root zone, and where reasonable, below the frost line.

The industry doesn’t have a standard for how deep to bury supply lines; however, some cities have ordinances on residential sprinkler main line depth. If there isn’t a local code, the depth takes into account factors specific to the sprinkler system components such as the size of the supply line, sprinkler heads, and risers.

With that being said, lines should be buried at a minimum of about five inches down, and most lines are buried within the top twelve.

Determining How Deep You Should Bury Your Sprinkler Lines

When burying your supply lines, the ultimate goal is to put them at the correct depth so the top of the sprinkler head is either flush with the ground or the head sits about one-quarter of an inch above grade.

If there is a local ordinance regarding depth, you want the lines to be deep enough they aren’t affected by mowing, aeration, or a light freeze, but you don’t want to bury them so deeply they are hard to access if they need repairs. Plus, deeper trenches equate to more labor during installation.

Many people start with an estimated depth, such as eight or ten inches, and then adjust the depth as needed for their circumstances.

To calculate the minimum depth to trench, you must add up the height of all of your system components—supply line, sprinkler heads—and then incoporate risers if needed to add height to your sprinkler heads.

How Big is the Supply Line?

The first factor in determining how deep to bury your sprinkler lines is the size of the pipe bringing water from the main to the individual heads. Depending on available water pressure, these sprinkler supply lines are typically three-quarters to one inch in diameter.

However, you need to put the pipe far enough underground that it is insulated from frost or a light freeze. You also want to ensure it isn’t easily disturbed or affected by activity above ground.

The minimum depth for supply lines and other pipes that run long distances is the pipe’s diameter plus four inches. You’d want to bury a one-inch supply line at least five inches below the soil surface.

Keep in mind four inches plus the pipe diameter is the minimum depth. In many cases people choose to bury lines deeper.

How Tall are the Sprinkler Heads? Will You Need Risers?

The length of the sprinkler head body impacts how deep you bury your lines and will dictate if you need to add risers to your system.

Most sprinkler heads are usually two, four, or six inches tall, varying with the head type.

• If you’re using a six-inch tall head, you’ll need to bury the line about six and three-quarters or seven inches below the surface, depending on the diameter of the supply line.
• If it’s a four-inch head, you must bury four and three-quarters or seven inches below the surface.
• If you’re using a two-inch sprinkler, you’ll have to add a two-inch riser to raise the head higher than the minimum extra four inches you’re burying the line.

Whether or not you need risers depends on the height of the sprinkler you’re using and local code (if applicable). Risers are plastic pieces that connect the sprinkler to the supply line and typically range from two to 12 inches tall. Risers help raise the top of the head to the soil surface.

With taller heads, you won’t need a riser if you’re only burying the line the minimal four inches. A six-inch sprinkler head doesn’t need a riser if you’re only intending on burying the line six inches deep. The shorter heads will need a riser to raise the top to the soil surface.

Risers are also helpful when burying your lines deeper for better insulation. While the minimum trench depth is four inches plus the diameter, most recommend burying lines at least eight or ten inches below the ground. You’ll need to add risers to get the heads to the surface when you go deeper.

Bury Sprinkler Lines Below the Grass

When burying your lines, you also want to ensure they are beneath the grass to keep the roots from tangling around the PVC and causing problems. Roots typically grow up to six inches long depending on the species you’re growing and your watering practices.

However, you should generally be safe if you’re following the minimum rule of supply line diameter plus four inches or using six-inch-tall sprinkler heads.

Do I Need To Bury Lines Below the Frost Level?

Upon first thought, most people assume sprinkler lines must be buried below the frost line in the ground to keep them from freezing in the winter. While this is a good practice, it’s more applicable in some areas than others and isn’t completely necessary.

The frost level, or frost depth or line, is how far below the surface level the soil may freeze in the winter. Or how deep the frost penetrates the ground when you’re hammered with extended periods of freezing temperatures.

When it comes to large “main” pipes, the International Plumbing Code (IPC) and the International Residential Code (IRC) state all water and sewer lines must be a minimum of six inches below an area’s typical frost level. This standard helps to ensure that the pipe can’t freeze.

This is easily applicable in southern areas of the country and along the entire western coast, as the frost level is typically about six inches deep. With a shallow frost depth, it’s easy to bury beneath it. However, the frost level can extend 100 inches into the ground in some northern climates! Burying beneath this depth isn’t feasible.

With sprinkler lines, it isn’t as important they get buried below the frost level as long as you shut off your sprinkler system each fall and winterize it properly. If the lines are blown out, you shouldn’t worry about them freezing and breaking.

However, burying your sprinkler lines six inches beneath is a reasonable safety precaution if you live in an area with frost levels within the top foot or so of the surface.