Fire Sprinkler Head Spacing and Placement Rules

What You Need to Know

Every sprinkler head must sit in the right spot. Too far apart and the water misses the fire. Too close to a wall or duct and the spray pattern breaks. AS 2118.1 sets the spacing and placement rules for automatic fire sprinkler systems in Australia. These rules change based on the hazard class of the space. Light Hazard offices have different spacing from Ordinary Hazard retail areas. Get the placement wrong and the system will not control the fire when it matters.

• The maximum coverage area for a standard spray sprinkler head is 12 m² with a maximum spacing of 4.0 m between heads (AS 2118.1)
• The minimum distance between any two standard sprinkler heads is 2.0 m (AS 2118.1)
• The maximum distance from a wall to the nearest sprinkler head is half the maximum spacing between heads - so 2.0 m at 4.0 m spacing (AS 2118.1)
• Sprinkler deflectors must sit between 25 mm and 300 mm below the ceiling (AS 2118.1)
• A clear space of at least 500 mm must exist below the sprinkler deflectors at all times (AS 2118.1)
• For high-piled combustible stock, the clearance below deflectors increases to 1,000 mm (AS 2118.1)
• You must install sprinklers under rectangular ducts wider than 800 mm and circular ducts wider than 1,000 mm diameter (AS 2118.1)
• Ducts with tops less than 500 mm below the ceiling count as beams for spacing purposes (AS 2118.1)
• If a duct has at least 150 mm clearance from the adjacent wall, the width limit increases to 1,000 mm for rectangular ducts and 1,200 mm for circular ducts (AS 2118.1)

Take a standard office floor with a 2.7 m ceiling height. Each sprinkler head covers up to 12 m² - roughly a 3.5 m × 3.5 m grid. You place heads no more than 4.0 m apart in any direction and no more than 2.0 m from any wall.

The deflector sits 25 mm to 300 mm below the ceiling soffit. Most pendent heads in office ceilings hang about 40 mm to 100 mm below the finished ceiling. If the ceiling void is tight, upright heads on the pipework above can work, but you still need that 25 mm minimum gap below the roof deck or slab.

The 500 mm clear zone below the deflectors matters. Nothing can block the spray pattern in this zone - not shelving, not signage, not cable trays. In a warehouse with racking stacked 4 m high, you need 1,000 mm of clear air between the top of the stock and the deflectors. If the racking goes higher, you may need in-rack sprinklers at intermediate levels.

Large ducts create shadow zones. Any rectangular duct wider than 800 mm blocks enough spray that you must put a sprinkler head underneath it. The same applies to circular ducts over 1,000 mm diameter. This catches most main supply and return air ducts in commercial buildings. Plan the duct routing and sprinkler layout together during the coordination phase, or you end up adding heads and branch piping later at extra cost.

The 2.0 m minimum spacing between heads stops water from one head cooling the next and preventing it from activating. This matters most in corridors and small rooms where you might be tempted to pack heads closer together.