How to Design a Sprinkler System for a Big Lawn

The design gods have given you an opportunity, and you have a rare chance to actually sit down and design a sprinkler system for a big lawn. You could design an irrigation system for a beautiful institutional lawn, golf course lawn, or landscape.

The basic physics, designs, or water dynamics doesn’t worry you. After all, you’re a professional. However, the fear of settling for outdated design methods makes you cringe.

The idea of making typical errors during the installation process that usually result in expensive repairs makes you a little nervous. Deep down, you have the primal need to stay professional. You want to:

• Establish an accurate GPM (Gallon per Minute) value for the new sprinkler system rather than depending on the erroneous measure-the-flow-from-faucet-with-a-bucket method (that always end up in sprinkler system flows that are too high for the existing house’s plumbing system to handle)
• Design sprinklers with almost 100% overlap to eliminate dry spots and avoid overrunning the sprinklers to water those dry spots (which overwaters some part of the lawn and doesn’t conserve water)

The good news?

It’s possible. With the right information on how to design a sprinkler system and the correct procedure, you can make a near-to-perfect design.

Step 1: Measure the Lawn Size That You Want to Install the Irrigation System On

The first step on how to design a sprinkler system is determining the actual size of the lawn.

Any mistake in lawn size measurement affects the entire design. In fact, many cases of sprinkler system replacement stem from inaccurate measurements.

That begs the question: How do you get the trick right?

1. Get a tape measure to take the lawn’s measurement. There’s no harm rounding off your measurements to the nearest foot. However, minor deviation to a couple of feet will result in dry spots.
2. Start by measuring the building perimeter in the lawn on your irrigation plan.
3. Since most buildings have straight sides and square corners—start taking measurements from one side of the building to establish an accurate base for the rest of your measurement.
4. Draw the lawn to scale on a piece of paper. For instance, you can use the scale of 1 square = 10 feet, depending on what works best.
5. Draw all other items on the lawn—like tree locations, pathways, and any other structures.

Now you have accurate lawn measurements.

Step 2: Measure the Water Supply That Will Power the Sprinkler System

Any sprinkler system operation depends on two critical aspects:

• Water flow
• Water pressure

Most sprinkler systems fail because of insufficient water pressure. To design a more accurate system, measure the flow rate and pressure.

However, don’t grab your bucket; turn on the existing faucet and time how long it takes to fill a gallon-size-bucket to measure the flow rate. There’s a smarter way.

If the institution’s water comes from a water company, ask for the property’s water pressure report. You’ll still need to measure the water pressure throughout the property, though, because it varies from one spot to another.

Use a water gauge as follows to get water pressure measurements at various spot:

• Turn off all the water inside the property 
• Then hook the water gauge to the outdoor spigot
• Turn on your outdoor spigot to full blast to measure your water output

Then find the flow rate value as follows:

• Identify the water supply pipe entering the institution 
• Measure the pipe’s circumference with a flexible measuring tape (strip any insulation first)
• Calculate the pipe’s diameter by dividing the circumference by Pi (3.142)
• Feed your pipe’s diameter measurement and water velocity value (from the water supplier) into this flow rate calculator to get an accurate flow rate.

Step 3: Design Irrigation Systems Using Hydrozones

Next, divide the lawn into several hydrozones to counter dry spots and other lawn diseases that stem from underwatering or overwatering. The practice entails grouping plants with similar water, sunlight, and soil needs.

For example, you can divide the lawn into:

Zone A: Routine Irrigation

This is the primary hydrozone that gets the most impact from the installation process of the sprinkler system. For instance, you can consider the lawn front as the principal hydrozone because that’s the most active and visually important part of any institution.

Zone B: Reduced Irrigation 

It’s a secondary hydrozone—visually important to the institution but less active. Perfect examples are flower beds or shrubs near the institution’s main entrance you’re making sprinkler system design for. For shrubs, you can get shrub sprinklers.

Zone C: Limited Irrigation

This is a minimal hydrozone—a place that receives little to no human use—justifying little irrigation. Such areas include buffer zones, distant views, and directional delineators such as grass strips between sidewalks and paths. Match these areas with native plants that survive with rainfall only.

Zone D: No Irrigation

These areas of the lawn will only receive rainfall and no extra water. They’re the least active regions like spots for utilities, naturally existing vegetation, or mulched parkways.

Step 4: Select Sprinkler Heads and Other Sprinkler System Equipment

Select preliminary pieces of equipment like sprinkler heads, control valves, and even a backflow preventer. The amount of pressure loss with each piece of equipment will influence your product decision.

However, stick to one sprinkler brand because not all sprinkler systems work the same. Below is a sprinkler system items table.

Sprinkler heads vary depending on the current watering need:

The Rotor Sprinkler Head

Rotor heads are excellent for large space areas. Since they have a low precipitation rate, they cover more area over a long period. Plus, rotor heads require less maintenance and can pass debris in reclaimed water without clogging.

The only problem?

The installation process of rotor heads is longer. However, the area of coverage and pressure loss of each rotor head will influence your buying decision. Since the brand matters, choose your rotor head from:

• Hunter
• Irritrol 
• K-Rain
• Orbit
• Rainbird
• Toro
• Weathermatic

Fixed Spray Sprinkler Heads

On the flip side, spray heads water to a small area and disperse more water for a shorter time. They are excellent for small hydrozones or areas around buildings. However, they require more maintenance because they’re susceptible to clogging.

As with rotor heads, go for top-notch brands, which include:

• Hunter
• Irritrol
• Orbit

Spray Heads With Rotary Nozzle

These are hybrids of spray and rotary that present versatile solutions for mid-size areas. The sprinkler heads have an excellent distribution pattern that goes down to 12 feet up to 28 feet.

You get the best of these from two brands:

• Hunter
• Rain Bird

Specialty Pattern and Bubblers

These are heads that solve particular landscape problems, such as a side or lawn end strip. Several companies deliver the best quality specialty pattern heads. Click on any of the five to buy:

• Atlantic Water Gardens
• Hunters 
• K-Rain
• Rain Bird

With the correct sprinkler heads, you’re ready to design the head layout.

Step 5: Design Sprinkler Heads Layout

You want to design the sprinkler system to deliver 100% overlap of the watered areas to eliminate dry spots.

To achieve head-to-head overlap, make the distance between heads to be the sprinkler’s radius. If the lawn has an odd shape, you can increase the inter-sprinkler spacing.

Alternatively, adjust the sprinkler’s radius (nearly all sprinklers have radius adjustment devices) to get the results you desire.

On a spray head, water pressure reduces when you close the small valve in the nozzle. On the flip side, the GPM of rotor sprinkler heads doesn’t change no matter how much you reduce the radius. Instead, it deflects water so that it doesn’t go far.

Step 6: Create Valve Zones and Draw-in Pipes for the Sprinkler System Design

Next, separate small sprinkler heads into clusters of different circuits depending on landscape architects—a control valve will control each cluster. Then, group valves together with a manifold and attach them to the irrigation controller.

After that, organize the pipes, fittings, sprinkler heads, and valves to work together. Then determine lateral pipe sizes.

The  6 Things That Matter When Designing Irrigation Systems for Big Lawns

By this point, we’ve covered a lot of technical details on how to design a sprinkler system. Sketch the irrigation system on paper—including the exact distance between the various parts of the sprinkler system like piping, valve, manifolds, and sprinkler heads. Then, make a list including all sprinkler parts.

To conclude, here are the six most important things to remember when designing a sprinkler system for a big lawn:

1. Start with taking the lawn size measurement.
2. Measure the amount of water that’ll power the sprinkler system.
3. Use hydrozone to design the sprinkler system.
4. Get the right sprinkler heads and other equipment from trusted irrigation brands. 
5. Design the layout of the sprinkler heads to deliver 100% overlap to eliminate dry spots.
6. Create valve zones and draw-in pipes and connect them to the irrigation controller.