The goal in adding an irrigation system to your yard is to have lush green grass and plants. If you install a sprinkler system and did not calculate your spacing properly between your rotors and or sprays you are likely to have brown, dry spots from under watering or have other areas in the lawn showing signs of over watering. Doing it right on the install is key. And if you keep in mind a few pointers it can also be simple to plan.
The absolute number one rule in spacing is called "Head-to-Head coverage" or Head-to-Head spacing. Head-to-Head coverage applies to both sprays and rotors. In a nutshell it means that the heads are spaced so that they overlap from head to head. Each head should throw water far enough so that it hits the next head. If you were to use a stand alone method you will most likely see dry brown spots in areas of your lawn due to insufficient watering. You may be able to add extra time watering as a remedy, however this is wasteful and costly. Imagine drawing circles that do not overlap, there would be areas that are not covered. If you used this method (known as a stand-alone method) you would certainly have areas that have left dry brown spots.
The factors to take into account when designing the spacing of your system may include:
- Sprinkler Head
- Water Pressure
- Type of Plants
- Wind Conditions
- Gallons Per Minute or GPM
Mark your sprays in the corners first and then if needed add your sprays along the perimeter. Proportions of the area can make placement simple. For example, a 30-by-60 foot lawn can be covered by six 30-foot rotors. One rotor in each corner and one in the middle of each of the 60ft sides. Dimensions that do not divide precisely can be calculated by adding a head in each corner followed by adding the fewest amount of heads required along the sides. If the area you are plotting is wider than the throw distance for your chosen head you will add additional heads down the middle if the section too.
Narrow areas can be watered using strip-pattern spray nozzles. Strip pattern spray nozzles disburse water in a rectangular pattern instead of a circular pattern. Three shapes are used to provide head-to-head coverage. A side strip is positioned along the side of a long strip. A center-strip is positioned in the middle or center. A corner strip is positioned in the corner, which has a spray arc that covers half of the side of the strip. Strip patterns generally cover widths of 4 to 5 feet and lengths of up to 30 feet.
For areas with curvy or irregular areas you will use spray heads with adjustable pattern nozzles. Adjustable pattern nozzles will allow you to adjust the spray throw to fit the area. There may be situations where equally spaced heads will not cover an area fully. Adding an additional head with smaller or greater coverage to fill in the space may be necessary. Try to keep over spray to a minimum and avoid areas that hit your house, fences, tree trunks or any surfaces that can be damaged by excessive moisture.
Rotors or Sprays?
The size of the area which needs to be irrigated is the main factor that will determine whether to use a rotor or a spray in any area in your irrigation layout. Rotors can cover a much greater area which makes them suitable for areas that are expansive. Some of the benefits of using rotors are that they can be spaced out farther apart which requires less heads to get the job done and less trenching. The maximum throw for a rotor is around 70 feet and the minimum throw of approximately 20 feet. There are some medium sized rotor models that can deliver a minimum throw as small as 15 feet. In comparison sprays throw water a much smaller distance (a maximum of around 15 feet and a minimum around 4 feet) so they are suitable for smaller areas in your design plan. Many irrigation designs will call for a combination of both rotors and sprays in addition to drip irrigation to evenly cover the landscape efficiently. Rotors and sprays can not be on the same zones however, because they require different water pressure rates to operate.
Rotor and Spray Performance Guidelines
Subtract an additional 10-15% from the recommended rotor or spray's maximum water throw for your desired model. Most manufacturers perform quality testing in controlled indoor environments. The tests are performed in artificial environments so that they can get results which are consistent, accurate and repeatable. Unfortunately this does give an accurate performance calculations on how your rotor or spray will perform in your yard when real life factors like wind and humidity exist.
Another pointer regarding sprays is to never turn a spray down more than 25% of it's rated throw because your distribution of water becomes poor (most manufacturer's note this point in their model specs).
Plotting Sprinkler Placement
You can take the principles from this sample and incorporate these principles in your design. There are two main types of spacing used in irrigation plans, square spacing or triangular spacing (also called staggered spacing).
* You will need a compass to plot your sprinkler placement on your plan.
Square spacing is the easiest to plot, the downfall is that there will be areas that are going to be covered by all four heads causing some over watering. Sprinklers are spaced relatively close when using a square pattern (on average around 50% of the diameter of the throw). This means you will also need more heads to cover an given area.
Triangular spacing is plotted using three points which means that more surface area is watered with less overlap .Since you can cover more surface using triangular spacing you will be able to space the heads farther apart (usually around 60% of the diameter of the throw). Using a triangular pattern in plotting sprinkler heads can save money because less heads are needed to irrigate any given area. To begin plotting using a triangular pattern start by choosing a side of a rectangular or square area as a baseline. Next plot a heads in each corner. Followed by placing the third head in between and across from the two you have plotted (see illustration as reference). When you go to plot the next row of your triangular pattern you will shift or stagger the pattern (similar to laying bricks).
General Guidelines and Special Situations
with a Walkway
Avoid watering the walkway by using a combination of spray patterns.
- 90 degree (quarter)
- 180 degree (half)
- 360 degree (full)
Placement of all three spray patterns combined.
Sample of each of pattern.
Placement of 360 degree paten.
Placement of 180 degree paten.
Placement of 90 degree pattern
Working with Corners around a Building
Triangular Shaped Spacing for Obstacles
Avoid an obstacle using triangular spacing.
Watering an irregular grouping of plants using triangular shaping.
Hedges & Lawns
Watering both the lawn and hedges simultaneously using a spray on a riser.
Reducing Water Loss on Corners
Reducing water loss on corners.
Irrigating the inside or outside of a curved area like a walkway.
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