AS 2118.1 Sprinkler Spacer — metric + friction demand

Hung-obstruction clearances — AS 2118.1:2017 Cl 5.7, Table 5.7.2 and Cl 5.7.9.3. Table values transcribed from the standard and re-checked cell by cell. The NCC sets where sprinklers are required (NCC 2022 Vol 1 Section E1); the clearance rules themselves are AS 2118.1. Installations must also satisfy Cl 5.7.7 (clear space) and Cl 5.7.8 (obstructions within it).

1 — Clearance from an obstruction (Table 5.7.2)

Sprinkler head type Dimension B — maximum deflector height above the obstruction (mm)

Dimension B is the maximum deflector height above the obstruction/beam. A negative B means the deflector must be installed below the obstruction by that amount (Table 5.7.2 NOTE).

Result
Next tabulated B ≥ your input	–
Required Dimension A — min. horizontal clearance	–

Table 5.7.2 as published — what A and B refer to

Dimension A is the minimum horizontal clearance from the sprinkler to the obstruction. Dimension B is the maximum height of the deflector above the obstruction or beam — a negative B means the deflector must be installed below it by that amount (see the standard's note at the foot of the table). A dash means the standard tabulates no value for that head type at that Dimension A, so compliance cannot be shown there. Reproduced from AS 2118.1:2017 Table 5.7.2.

2 — Sprinklers below a duct, bulkhead or beam (Cl 5.7.9.3)

Obstruction shape Rectangular (duct, bulkhead, beam) Circular

Clearance from adjacent walls 150 mm or less More than 150 mm

Obstruction width (mm)

Top of obstruction below the deflector (mm)

Result
Width trigger for this configuration	–
Clear space required below deflector (Cl 5.7.7)	–
Sprinklers required below the obstruction	–

Cl 5.7.9.2 (overhead platforms, galleries, stairs, chutes) uses the same 800 mm / 1 m + 150 mm wall-clearance thresholds and is not covered here.

Where this differs from the source workbook. The lookup and the calculation above were re-checked against AS 2118.1:2017 and correct four things in Hung Obstruction Lookup.xlsx — the width trigger is greater than or equal to (a duct exactly on the trigger width requires sprinklers, where the sheet returned “No”); the trigger width depends on the clearance to adjacent walls (800/1000 mm rectangular, 1000/1200 mm circular), which the sheet did not ask for and so applied the more permissive figure in every case; the < 500 mm height test now affects the answer rather than only printing guidance; and units are mm throughout where the sheet mixed mm and metres. Sheet 1’s Table 5.7.2 values were verified cell by cell and needed no change.