In order to get maximum uniformity, sprinklers should be spaced at their radius. Viewed from above, this creates a grid-like pattern in irrigation design with sprinklers spaced head to head both horizontally and vertically. The example below assumes a set of sprinklers with a 3m radius designed for a rectangular shaped section of garden 12 metres by 6 metres.
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We call this type of spacing “square spacing” because of the pattern it makes if you draw a line between 4 sprinklers. This is the most common type of spacing and it works well with areas that are roughly square or rectangular. If you picture the sprinklers operating you will notice that each square gets spray from 4 different sprinklers. This overlapping is essential to get uniform precipitation and is the correct way to design a sprinkler system. The other common way to space is triangular spacing. The next example shows triangular spacing in a similar area to the first example and using the same sprinklers.
If you draw a line between three adjacent sprinklers the pattern formed is an equilateral triangle (all three sides are equal at 3 metres). Basic geometry tells us that the altitude of the triangle is 0.866 of the radius; in this case it works out to 2.6 metres. This means that the vertical spacing must be 2.6 metres to get full head to head coverage. You will note that there are sprinklers missing along the left and right sides. On the left there is a space in the middle with no sprinkler and along the right there are no sprinklers in the corners.
This is the downfall of triangular spacing. It is great for large open areas, but in smaller areas it becomes difficult to fit the spacing to the shape of the landscape. In this case we would have to place “filler” sprinklers in the spots the triangular spacing omits.
Triangular spaced sprinklers have a higher rate of precipitation (ROP) than square spaced sprinklers. A typical cone sprinkler will have a ROP of 40mm/hr for square spacing while triangular spacing yields 46mm/hr. See our article on calculating precipitation rates.