Fire Services for Multi-Storey Residential (Class 2)

What You Need to Know

Class 2 buildings (apartments, units, residential flat buildings) have specific fire service requirements under NCC 2025 Volume One. The triggers for sprinklers, hydrants, detection systems, smoke exhaust, and stairwell pressurisation depend on the building's effective height and rise in storeys. Getting these triggers wrong at the design stage means costly redesign or, worse, failed compliance at the Construction Certificate (CC) stage.

A typical 4 to 8 storey apartment building in NSW requires fire hydrants, a fire detection and alarm system to AS 1670.1, smoke detection in common areas, smoke alarms in every sole-occupancy unit, and depending on height, sprinklers and stairwell pressurisation. The fire services package for a Class 2 building commonly represents 8% to 15% of the total building services cost, and that figure rises significantly once the sprinkler threshold is triggered.

This memo covers the NCC 2025 fire service requirements for Class 2 buildings, the key thresholds that trigger each system, and the practical decisions that affect cost, programme, and compliance. It is written for contractors, developers, and architects who need to understand what fire services are required before engaging a fire engineer.

• Sprinkler system (AS 2118.1) is required when the building has an effective height greater than 25 metres, or a rise in storeys of 4 or more. The system must cover all habitable areas, corridors, storage cages, plant rooms, and car parks. A residential sprinkler system under AS 2118.1 typically requires a dedicated fire pump set, on-site water storage tank (minimum 15,000 to 40,000 litres depending on building size), and a connection for the fire brigade booster. (NCC 2025 Specification E1.5, Table E1.5)
• Fire hydrant system (AS 2419.1) is required for Class 2 buildings with an effective height greater than 25 metres, a floor area exceeding 500 m2 per storey, or a total floor area exceeding 2,000 m2. Hydrants are installed in fire-isolated stairways or on each level at hose distances not exceeding 4 metres from the furthest point on the floor. The system includes a fire hydrant booster assembly at the street frontage. (NCC 2025 Specification E1.4, AS 2419.1:2005)
• Fire detection and alarm system (AS 1670.1) is required for Class 2 buildings with a rise in storeys of 4 or more, or an effective height greater than 25 metres. The system includes a fire indicator panel (FIP) at the main entrance, smoke detectors in common corridors, lobbies, and plant rooms, thermal detectors in car parks, manual call points at exits, and occupant warning speakers or sounders on every level. (NCC 2025 Specification E2.2a, AS 1670.1:2018)
• Smoke alarms (AS 3786) are required in every sole-occupancy unit regardless of building height. Alarms must be installed in every bedroom, in every hallway connecting bedrooms to the rest of the unit, and on every storey of a multi-level apartment. For buildings with fewer than 4 storeys, interconnected smoke alarms within each unit may satisfy the requirement without a full AS 1670.1 system. (NCC 2025 Part E2, EP&A Regulation 2021 Clause 189)
• Stairwell pressurisation (AS 1668.1) is required for fire-isolated stairways serving buildings with an effective height greater than 25 metres. The system maintains a minimum pressure differential of 50 Pa across closed stairwell doors to prevent smoke from entering the escape path. A typical system includes a dedicated pressurisation fan, relief dampers, barometric dampers at each level, and BMS integration for fire mode activation. (NCC 2025 Specification E2.2a, AS 1668.1:2015)
• Smoke exhaust system (AS 1668.1) may be required for common corridors, lobbies, and basement car parks. For corridors serving Class 2 buildings, the NCC requires either natural ventilation (openable windows with aggregate area of at least 5% of corridor floor area) or a mechanical smoke exhaust system. Basement car parks require mechanical exhaust capable of 6 air changes per hour in normal mode and higher rates in fire mode. (NCC 2025 Part E2, AS 1668.1:2015, AS 1668.2:2024)
• Fire separation between units requires fire-rated walls and floors between each sole-occupancy unit. Walls separating units must achieve a fire resistance level (FRL) of typically 60/60/60 for buildings up to 4 storeys and 90/90/90 for buildings above 4 storeys. All service penetrations through fire-rated walls and floors must be sealed with tested and listed fire collars, wraps, or sealants. (NCC 2025 Part C, Specification C1.1, FRL requirements)

Sprinkler and hydrant water supply. When both sprinklers and hydrants are required, they can share a common water storage tank and pump set, but the tank capacity must satisfy the simultaneous demand of both systems. AS 2118.1 requires a minimum sprinkler flow duration of 30 minutes for residential occupancies, and AS 2419.1 requires a hydrant flow duration of 30 to 60 minutes depending on building classification. A combined tank for an 8-storey, 80-unit apartment building is typically in the range of 30,000 to 50,000 litres. The tank is usually located at basement level or ground floor, with the pump set adjacent. The fire brigade booster at the street frontage allows the fire brigade to supplement pressure in the system.

Detection and alarm integration. The AS 1670.1 fire detection system connects to a fire indicator panel (FIP) located at the main entrance or in a fire control room for larger buildings. The FIP displays the zone and location of any alarm activation. In buildings with mechanical services, the FIP sends a signal to the BMS to activate fire mode, which typically shuts down normal HVAC, activates stairwell pressurisation fans, switches car park ventilation to smoke exhaust mode, and closes fire and smoke dampers on the relevant zone. This interface between fire detection and mechanical services is critical and must be coordinated between the fire engineer, mechanical engineer, and electrical engineer.

Stairwell pressurisation design. The pressurisation fan is typically located at the top of the stairwell or on the roof, with a dedicated shaft or ductwork delivering air to each level. The system must maintain 50 Pa across a closed door with all doors closed, and must not exceed 110 N of force to open the door (to allow occupants to escape). This means the system needs relief dampers or variable speed drives to manage pressure when doors are opened or closed during evacuation. A typical 8-storey stairwell pressurisation fan handles 2,000 to 4,000 L/s of supply air depending on the stairwell volume and door leakage characteristics.

Smoke exhaust in corridors and car parks. Common corridor smoke exhaust systems extract smoke from the fire-affected level while maintaining tenable conditions for occupants evacuating through adjacent corridors. The system is activated by the fire detection system and operates on dedicated fire-rated power supplies. Basement car park smoke exhaust serves a dual purpose: normal ventilation for vehicle emissions (typically 7.5 L/s per m2 of car park area under AS 1668.2) and emergency smoke exhaust in fire mode. The car park exhaust fans must be rated for operation at 250 degrees C for 120 minutes when serving as smoke exhaust fans.

AFSS and ongoing compliance. Once the building is occupied, all fire services are listed on the Annual Fire Safety Statement (AFSS). The building owner must engage accredited practitioners to inspect, test, and certify each fire safety measure annually. Sprinkler systems require quarterly and annual inspections to AS 1851. Hydrant systems require six-monthly and annual testing. Stairwell pressurisation and smoke exhaust fans require annual testing under AS 1851 and the essential services schedule. Failure to maintain the AFSS is an offence under the EP&A Regulation 2021 (NSW) with penalties up to $110,000 for individuals.