Head-to-head: why your lawn needs it
Head-to-head spacing is the #1 rule in professional irrigation design for consistent green coverage.
The non-uniform spray problem
Spray nozzles do not distribute water evenly across their throw radius. Precipitation rate is highest near the nozzle — roughly 80–100 % of rated output — and drops sharply toward the outer edge, where it falls to 20–40 %. This gradient is by design: the outer edge of a correctly spaced sprinkler is supposed to overlap with the inner zone of the adjacent head, adding the two distributions together.
When heads are spaced too far apart, the two distributions no longer overlap. The area between them receives only the weak outer-edge output from both sprinklers — typically one quarter to one third of the central rate. After a few weeks you see dry bands, yellowing turf, and compacted soil between irrigation tracks. Increasing run time does not fix this; it only makes the overwatered centre worse.
What head-to-head means in practice
Head-to-head coverage means each sprinkler throws water at least to the position of the adjacent sprinkler head. A nozzle rated at 4 m radius should be placed no more than 4 m from the next head. In the field, allow a 10–15% reduction: if the nozzle catalog says 4 m at 2.5 bar and your supply is 2 bar, expect roughly 3.4 m of real throw and space accordingly.
The rule applies in both axes of a grid layout. In a rectangular lawn, the critical constraint is usually the short dimension. A 6 m wide strip with heads on both long sides requires each head to throw at least 3 m to achieve true head-to-head. If your nozzle only reaches 2.8 m under real pressure, you need a smaller-radius nozzle or a third row of heads down the centre.
Why professionals never skip it
Reducing head count to save material cost is the most common field shortcut, and the one most reliably reversed over the following summer. Dry spots require reseeding, weed suppression and often manual watering — easily exceeding the cost of the sprinklers that were removed. Oversized spacing also forces longer run times to compensate, consuming more water for worse results.
Distribution Uniformity (DU) measures how evenly a system applies water. A well-designed head-to-head layout achieves DU above 70–75%. Stretched spacing typically produces DU of 40–55% — meaning some zones receive less than half the water that other zones receive in the same run time. At that uniformity level, it is physically impossible to keep the entire lawn healthy with a single schedule.
Practical grid placement
Start layout from the corners. Place a 90° head in each corner, pointed inward. Then work around the perimeter: space mid-side heads at the head-to-head distance for your chosen nozzle. Only after perimeter heads are placed should you check whether the centre needs additional heads to fill any remaining gap.
Avoid placing heads in the middle of a zone before the perimeter is fixed — a common amateur error that results in off-centre spacing and wasted throw toward paths or walls. On narrow strips under 3 m wide, a single row of 180° heads along one edge covering the full width is usually sufficient and more efficient than two rows of 90° heads facing each other.
Common mistake: radius inflation
Catalog throw distances are measured at a specific test pressure, often 2.1 or 2.5 bar, in windless conditions. Real installations frequently run at lower pressure with pipe friction losses and multiple open heads competing for flow. Assuming catalog radius at real-world conditions leads to systematic spacing errors.
Measure static and dynamic pressure at the tap before finalising the design. With a pressure below 2 bar, choose nozzles rated for low-pressure operation, or use rotary nozzles (rotators) which are less sensitive to pressure variation and still achieve good uniformity at 1.5–2 bar. Stretching spray nozzle spacing beyond their actual field radius is a mistake that appears only weeks after installation.
Head-to-head standards in the US and UK
In the US, the Irrigation Association (IA) and ASABE define distribution uniformity (DU) targets for residential turf: DU ≥ 70% for fixed-spray systems, ≥ 75% for rotary nozzle systems. These benchmarks directly translate to head-to-head spacing. Rain Bird nozzle selector tools and Hunter design guides both use head-to-head as the primary layout constraint.
In the UK, the Irrigation Association UK and CIBSE TM64 reference the same head-to-head principle. Typical domestic supply pressure in England is 2–5 bar static; dynamic pressure at full-zone draw is 1.5–3 bar depending on pipe length and meter size. Rain Bird and Hunter provide UK-specific radius charts adjusted for 50 Hz supply conditions.
SprinklerMap Team — Irrigation technical guides
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