how to divide your yard into zones

Drawing the Layout

Now we get into design. At first glance it might sound intimidating but don’t worry. Everything is broken down into bite size chunks.

By now you should have drawn the property. If you have not, go HERE first, then HERE. You will want to look at both pages. Your basic drawing should look something like this sample of a front yard drawing.

Look at each zone (flower bed, grass, etc.) and visualize how the heads should be laid out. For example, if you have a planter you should get an idea of where the heads should go. For great help and guidance, go HERE.  Remember this important point: you must have head to head coverage. In other words, the water from one head should hit the next head. Draw your circles on your plan. Use a pencil. Check the samples given below.

  If you can’t quite visualize something, go outside to the problem areas. Take some pin flags to mark where the heads might go. If possible, take a number of colors, one for each zone. Don’t be afraid to move and change the pattern as you go. It takes a bit of practice to get it right. Staking out your property is covered in the next paper.

Remember that slopes are slippery creatures. The water has a tendency to run off. So if your yard is 2/3 flat and 1/3 slope you need to put the slope on its own zone. That way you can customize the watering schedule to avoid run off.

Spray heads have two basic factors: range and pattern. For example, a spray head might have a 15’ radius and a half circle. This is a 15’half or 15H.  12Q is a spray head with a 12’ radius and a 90 degree pattern. Common distances are 8, 10, 12 and 15 feet. There are shorter and longer available for special situations. Check HERE for examples.

Rotors can go out to about 50’ on most residential systems. That’s pushing it to the limit. Degradation of the system over time will cause coverage loss. Even a decent breeze will cause coverage loss. Try to use 40’ as your working maximum. Saves trouble later. They have interchangeable nozzles to allow for distance settings. Examples are HERE

There will be a temptation to say “Hey! I have a huge open back yard! I can put in a few rotors and do it all at once and cheaply too!”  Well, if you have enough pressure you possibly can. However, rotors are great for baseball fields and golf courses and places where the landscaping will never change. If you make changes later to your yard, say a planter or a pool or an outdoor patio, then not only will rotors not be effective but you will be limited in the changes you can make without lots of shovel work. Shovel work = no fun.

Your layout might look something like one of these:

You might ask “Hey! What about drip? You mentioned drip, didn’t you?”  Yes, I did. And you might take a look at this overview of drip but right now don’t worry about it. Let’s keep things simple. We only care about zones. Trust me; if you have enough water to put spray heads in your planter you have more than enough for drip. We’ll get back to it someday.

Now the fun begins. We get to play with math. Your teacher was right all those years ago when they said you would use math all your life.  Luckily ours is simple. And we let you cheat. We need the meter size, which you have, the supply pipe size (the pipe coming out of the meter) and your GPM. Now we just go to a chart.

Find your water meter size, then your service line size, cross over to the column with your water pressure and you magically get your GPM and working pressure. Now we have our working pressure and gallons per minute.  So a 1” meter with a 1” service line at 50psi gives you 14 GPM at 35psi. Simple.  Now we can design our zones.

Go back to the layout you just did. Pick a zone. Count the number of spray heads, their patterns and radius. For example, you might have:

Now go to the brand of nozzle you want to use and fill in the flow rates. These are fairly typical rates: a 12 Full uses 2.93 GPM, a 1 Half uses 1.42 GPM, and a 12 Quarter uses .72 GPM. Let’s add this to the chart.

Well, we know that we only have 14 GPM available and we need 19.47. In this case we would split this area into two zones. Now it doesn’t make a lot of difference in theory if you make one 13gpm and one 7gpm but there are some other considerations. First, we sorta like balance and symmetry. Two 10gpm zones just sounds better. On a more practical note, if you make one zone 13gpm you limit any future expansion to zero. With two 10gpm zones you can add heads in the future. There is one other issue that will be discussed at the end of the paper.

What? You have rotors? Same thing without worrying about patterns.

Typical rotor GPM at 35psi (your working pressure): 40’ = 3.5gpm, 30’ = 1.4gpm. Since we need 24gpm for the rotors and have 14gpm available we’ll need two rotor zones.

Where do you find the gpm information?  Go to the page of knowledge. On this page you will have a chance to look at all the major brands of rotors and spray heads/pop ups. Each product will have a reference that will give you the gpm. A STRONG, STRONG WORD OF ADVICE: don’t mix brands in a zone.  I don’t care if you have Rain Bird pop ups/spray heads and K-rain rotors. That’s fine. But don’t put K-Rain and Irritrol rotors in the same zone or Toro and Signature spray heads in the same zone.  Each brand has what is called ‘matched precipitation’, in other words a consistent volume of water over time. Mixing your brands can cause uneven coverage.

You have now basically divided your yard into zones. It will probably take more than you thought. That’s expected.  One word of caution: in the sample above I showed where you could divide an area into two zones, one using 13gpm, which is almost the maximum allowed. Try to avoid this for two reasons. First, systems do degrade. Using 10 or 11 allows for continued consistent performance over time. Another issue is friction loss. We will NOT get into friction loss here or later if I can help it. Just realize that every foot of pipe, all the fittings and valves cause pressure loss. You’ll need the extra head room in the design.

Now you have your zones. Time to figure out the pipe layout. That’s another article.