The distance between sprinkler heads is the primary factor for an efficient and healthy lawn irrigation system. Proper spacing achieves uniform water distribution, preventing dry spots from under-watering and wasteful runoff from over-watering. If heads are placed too far apart, water patterns will not overlap sufficiently, leaving parched areas. Placing them too close wastes hardware and leads to excessive water application. Correct placement directly influences water usage efficiency and turf health consistency.
The Head-to-Head Coverage Principle
The fundamental rule governing sprinkler placement is the “head-to-head” coverage principle. This means the water stream from one sprinkler head must reach the location of the next sprinkler head in the line. This ensures that every point within the irrigated area receives water from at least two, and often four, sprinkler heads, creating the necessary overlap for uniform coverage.
The application of this principle depends on the type of sprinkler head being used. Fixed spray heads are designed for smaller areas, typically having a maximum throw distance of about 15 feet. Therefore, the maximum spacing between two fixed spray heads should be 15 feet, or slightly less, to guarantee the throw from one reaches the next.
Rotary heads distribute water over a greater distance by rotating and are suited for larger lawn areas. Rotor heads can have a throw range between 20 feet and 70 feet, allowing them to be spaced farther apart than spray heads. The head-to-head rule remains constant: the distance between any two rotor heads should not exceed the radius of their throw. Because spray and rotor heads have different application rates, they should never be mixed on the same irrigation zone, as this prevents uniform watering.
Factors Influencing Throw Distance
The actual working distance, and thus the required spacing, of a sprinkler head is not a fixed number and is strongly influenced by operational conditions. Water pressure, measured in pounds per square inch (PSI), is one of the most significant factors. As pressure increases, the distance the water is thrown also increases, up to a point.
Excessive water pressure can be detrimental, causing the water stream to atomize or break up into a fine mist (fogging). These smaller water droplets are susceptible to wind drift and evaporation, reducing the effective throw distance and pattern uniformity. To ensure performance matches manufacturer specifications, measure the PSI at the head. Installing pressure regulators may be necessary to keep the system within the optimal operating range, often around 30 PSI for fixed spray heads.
Nozzle selection also modifies the throw distance and application rate, directly impacting the necessary spacing. Nozzles are interchangeable components that determine the size of the water flow and the angle of the spray. A larger nozzle size generally allows for a greater wetted radius, but it also demands a higher flow rate to operate efficiently.
Environmental factors, especially wind, require a reduction in the calculated spacing. Wind causes water to drift away from the intended target area. In consistently windy locations, it is necessary to decrease the distance between heads by 25% or more compared to the manufacturer’s suggested spacing to maintain head-to-head coverage.
Layout Patterns and Perimeter Spacing
Once the maximum operational spacing is determined, the heads must be arranged in a geometric pattern to maximize uniformity. The two most common layout patterns are the square and the triangular (or staggered) arrangement. The square pattern is the simplest to plot, where each head is positioned at the corner of a square or rectangle, making it ideal for rectangular turf areas.
The triangular pattern staggers the heads in alternating rows. This arrangement provides a more uniform distribution of water, especially in areas with moderate wind. While more complex to lay out, the triangular arrangement can allow for a slightly wider spacing than the square pattern while still achieving excellent coverage.
A specific rule applies to placing heads along the boundaries of the irrigated area, such as near sidewalks, driveways, or fences. Heads along the perimeter should be placed at half the full spacing distance from the edge. This half-radius placement ensures that the water reaches the edge of the turf without spraying onto non-landscaped areas.