How to Install an Underground Sprinkler System

Living landscapes need water to survive and flourish, but relying completely on natural rainfall isn't always a reliable way to supply water. An underground sprinkler system offers the convenience of spraying water directly where it needs to go and the opportunity to automate your watering schedule according to your needs. DIY sprinkler system installation can save you money.

To decide if you need an underground irrigation system, consider:

• The type of grass in your lawn will affect irrigation needs.
• Some turfgrass varieties have higher water requirements than others.
• Your soil type also affects the efficiency of irrigation. For example, sandy soils absorb water more quickly than clay.
• An irrigation system gives you better control of the moisture content of your soil, but supplying more water than the soil can absorb will create runoff.

Planning and purchasing the correct components are the keys to a successful lawn sprinkler system. But don't be discouraged; most manufacturers of home irrigation systems have design and planning guides that simplify the job considerably.

Before installing a permanent irrigation system, you'll need to:

• See if your locality requires a building permit.
• Check for underground utilities before digging.
• Research your local municipal watering ordinances.
• Find out if your state/local regulations require a licensed professional installation.

To purchase the right components, you'll also have to determine specific information about your home:

• Water pressure in pounds per square inch (PSI)
• Water meter size (for a municipal system) or well pump size (for a well)
• Water service line size
• Water flow rate in gallons per minute (GPM)
• Type of backflow prevention required by local code

If you're on a municipal water system, you should find the size printed on the meter itself. If you can't locate it, look on your utility bill or call your water provider. Water meters are 5/8 inch, 3/4 inch or 1 inch.

If your water comes from a source other than a municipal system, such as a well, you'll need the pump size. Look in the owner's manual or if necessary, contact the manufacturer.

To match the size of the irrigation pipe to your existing water service, you'll need to determine the size of your incoming supply line. To do so, get a piece of string and wrap it once around the water pipe. Measure the length and compare it to the chart below.

1. Using your outside spigot, fill a measurable container with water.
2. Record the time it takes to fill to a measurable level; a gallon is the easiest amount.
3. Divide the filled container size (in gallons) by time (in seconds) it takes to fill it.
4. Multiply by 60 seconds.
5. The number you get is the flow rate in GPM. Multiply that number by 60 if you need to determine gallons per hour (GPH).

When you've completed all of the preliminary research, it's time to start laying out your system. Most yards have a variety of elements that have to be considered when laying out an irrigation system:

• Shrubs or other foundation plantings
• Flower beds or mulched areas
• Trees
• Sidewalks
• Fences and other installed features
• Slopes
• Areas of sun and shade

Because of these features, you'll most likely have to create more than one watering zone. The number of zones you need also depends on the GPM your system can supply. A zone (or circuit) is an independently contained set of pipes and sprinkler heads. Zones are determined by the physical attributes of your landscape and the capacity of your water supply. Each zone has its own control valve.

A map is essential to establish watering zones. Begin by measuring and mapping your property to scale on graph paper. A scale of 1 inch = 10 feet is best. The map should include the house and all permanent landscape features. Mark the location of the water meter on the map.

Landscape features need to be clearly marked so that the installed system will provide complete coverage for only the areas that need water. Note prevailing winds if you feel they'll affect coverage. More importantly, mark sloping areas in your lawn. If your yard is sloped, the water pressure changes (lower as the elevation increases, higher as it decreases), affecting the amount of water delivered by the sprinkler.

You'll also need to draw where the manifold will be located. The manifold needs to be located in an inconspicuous spot near the water supply line.

PVC pipe (polyvinyl chloride pipe) is the most common irrigation material. The familiar rigid, white material is stronger than polyethylene. Connections are made with adhesive.

Polyethylene is flexible, so it’s often used in cold climates to adapt to extended freeze cycles. Polyethylene comes in rolls and can be curved around natural and human-made obstacles, requiring fewer fittings than PVC. Connections are made with specially designed clamps.

Both types of pipe are cut with a hand saw or pipe cutter. A pipe puller is great for installing polyethylene pipe but requires a little expertise to operate. Unless you want to get some on-the-job training in your front lawn, this machine is probably best left to the professionals.

The design is done, the parts are selected and now you're ready to learn how to install a sprinkler system. Lay out the location of the lines with stakes and string. Place a flag or other marker where the sprinkler heads will be located. The trenches will be relatively shallow, usually 6 to 12 inches deep, depending on your area's freeze cycles and frost severity. The trench must also be deep enough to allow the sprinklers to retract underground to prevent breakage from lawn machines.

Dig the trench by hand or rent a trencher (a real timesaver). If you choose to dig by hand, a garden spade with a square edge is the best tool to use. A ditch spade is also pretty handy for working in a narrow space. Dig by hand in flower or shrub beds to prevent damage to the plants.

The trenches must be level. If some heads are lower than others, gravity will reduce efficiency. Dig only as much as you can install in each work session. Save the sod to re-cover the trench.

Assembly is a snap once all the planning is complete. Lay out the pieces first. If possible, assemble parts before putting them in the trench. It's best to start at the manifold and work outward when connecting the components.

There are two ways to connect your irrigation system to the water supply:

• The valve can be connected (like a garden hose) to an existing outdoor faucet, which is usually located directly outside the house.
• The system can also be connected directly to the service line. First, shut off the water supply. Between the main shut-off and the house, cut a 1-inch section out of the service line. Add a compression tee fitting and an additional valve to allow the system's water supply to be controlled independently of the house system.

• You probably want 1 to 2 inches of water per week, depending on your vegetation. Measure water by placing a cup or other container in each zone. Run the system for a regular cycle and measure the amount of water in the container. This will tell you how long your system needs to run to get the right amount of water.
• At the end of the season in colder regions, you may need to blow out residual water from the system before the ground freezes. Compressed air is the normal "tool" used. Find a professional to do this task.
• Exposed backflow preventers and valves may need to be protected from freezing.
• Part of your ongoing maintenance program is observation. Don't wait for brown spots to appear; watch out for clogged sprinkler heads or pipes.

You may need to prepare your system for winter to avoid damaging or breaking pipes and connections. In temperate and warm regions, you may get away with simply covering aboveground piping with insulation; the ground in these climates typically doesn't get cold enough to freeze. For colder climates, this winterization process can be a DIY job, but it might be beneficial to hire a professional, especially for larger landscapes.

To ensure your system is properly protected, consult the owner's manual or manufacturer for best practices.

To Winterize:

1. See if your system has auto-drain valves. If so, simply turn off the water supply, open the valves and allow excess water to drain from the system. This one step is sufficient to winterize underground irrigation systems with auto-drain.
2. If you have manual drains, you'll need to use an air compressor with pressure between 50 and 100 PSI. A small air compressor with lower PSI won't be able to clear water from your system.
3. Open the valve manifolds to allow any remaining water to drain.
4. Hook up the air compressor and run air through each zone in your system until you've cleared all zones of water.
5. Remember to turn off the timer to avoid additional water from entering the system.