Plant Room Design and Access Requirements

What You Need to Know

Plant rooms hold the equipment that keeps a building running. Chillers, pumps, switchboards, fire pumps, air handling units, boilers, and generators all live in these spaces. Get the room too small and you cannot maintain the gear. Miss a clearance rule and you fail compliance. Every discipline has different requirements, and they all share the same room.

• Mechanical equipment needs at least 1000 mm clearance from walls on all service sides (AS 1668.2, general practice; AIRAH DA09)
• Pump-to-pump spacing should be at least 1500 mm to allow valve access and impeller removal (industry standard)
• Minimum headroom in plant rooms is 2100 mm clear above finished floor level, though 2400 mm is preferred for overhead pipe and duct runs (NCC, AS 1657)
• Switchboards need 1.0 m clearance from all accessible faces. For domestic, this drops to 0.6 m (AS/NZS 3000, Cl 2.10.2.2)
• Switchboards rated 800 A or more per phase, or longer than 3.0 m, need two emergency exit paths spaced well apart (AS/NZS 3000, Cl 2.10.2.2)
• Switchboard room doors must be at least 900 mm wide by 2200 mm high and open outward (AS/NZS 3000)
• Plant rooms need mechanical exhaust ventilation. The typical minimum is 5 air changes per hour for general mechanical plant rooms (AS 1668.2)
• Fire pump rooms must be fire-separated from the rest of the building. Walls must match the building’s required fire resistance level. Doors need a minimum 30-minute fire resistance and must open directly to outside (AS 2419.1)
• Diesel fire pump rooms need exhaust discharge at least 2.7 m above the nearest path of travel (AS 2419.1)
• All plant must sit on concrete plinths, typically 150 mm high minimum, to keep equipment above any floor-level water (general practice)
• Plant room floors must fall to floor drains. Provide hose bibs for washdown (NCC, AS/NZS 3500)
• Access platforms, walkways, and ladders must comply with AS 1657 for safe access to elevated equipment (AS 1657:2018)
• Equipment that weighs more than what one person can lift needs lifting points or a designated equipment hatch (WHS Regulations, AS 1657)

A typical 500 m² commercial office building might have a single plant room on the roof holding a packaged air-cooled chiller, an air handling unit, a small switchboard, and a fire pump. That room needs to be big enough for every piece of equipment plus all the clearances around each one.

Start with the chiller. A 300 kW air-cooled chiller is roughly 4000 mm long, 2200 mm wide, and 2200 mm tall. Add 1000 mm on three sides for maintenance and 1500 mm on the condenser side for airflow. That single machine needs a footprint of about 5500 mm by 4700 mm, or 26 m², just for itself.

Now add the AHU. A typical unit for this building size is 3500 mm long and 1500 mm wide. With 1000 mm clearance on each side and 600 mm for filter pull, that adds another 16 m².

The switchboard needs 1000 mm in front and 600 mm behind (if rear access is needed). The fire pump needs its own separated room with a fire-rated door to outside.

Add in pipe runs, duct connections, a BMS panel, and walkways between equipment, and you are looking at 60 to 80 m² for a building of this size. Under-sizing is the most common mistake. Once the steel is up, you cannot make the room bigger.