Our Ballarat build has the ensuite exhaust fan venting into the roof space. The builder says that's how it's always been done, but the energy assessor disagrees. Do exhaust fans have to duct outside now, and what flow rates apply?

The assessor is right, and this is not a new rule the builder has been caught out by. Exhaust from a bathroom or sanitary compartment must discharge directly, or via a shaft or duct, to outdoor air. Discharging into the roof space does not satisfy the provision. [1]

Three separate things get conflated in this argument, and they are worth pulling apart before anyone digs in:

• Where it discharges and how hard it works is a condensation and ventilation question, governed by 10.8.2. [1]
• Whether it seals when it is off is an energy efficiency question, governed by 13.4.5. [3]
• Whether the fan is an approved product under the Victorian Energy Upgrades scheme is neither, and is the trap in this one. See below.

The flow rates. The minimum rates are set by room type: [1]

• bathroom or sanitary compartment: 25 L/s
• kitchen or laundry: 40 L/s

The two requirements people forget. Both sit in the same provision and both routinely get missed at inspection:

• Make-up air. Except for a room naturally ventilated under 10.6.2(a), a room with an exhaust system must be given make-up air, either through openings to an adjoining room with a free area of not less than 14,000 mm2, or in accordance with AS 1668.2. [1] The worked example is the practical one to design to: a 20 mm undercut on a 700 mm wide door achieves the 14,000 mm2. [2]
• Interlock and run-on timer. An exhaust system serving a bathroom or sanitary compartment that is not run continuously and is not naturally ventilated must be interlocked with the room's light switch, and must include a run-on timer that keeps running for 10 minutes after the light is switched off. [1]

Sealing. An exhaust fan serving a habitable room in climate zones 4, 5, 6, 7 and 8 must be fitted with a sealing device, such as a self-closing damper or a filter. [3] Ballarat is well inside that band on any reading, but confirm the zone for your specific site rather than assuming, because the same table drives other numbers on the job.

"It has always been done that way" does not survive the check. The discharge requirement and both flow rates are materially unchanged from NCC 2022, which carried the same 25 L/s and 40 L/s and the same discharge to outdoor air. [4] The sealing requirement is identical between editions too. [5] So the practice was not compliant under the previous edition either. Victoria moved to NCC 2025 as the sole edition on 1 May 2026, with no election window, which removes the one argument that might otherwise have been available.

The Victorian trap worth knowing. The Victorian Energy Upgrades specifications, for product categories 15C and 15D, permit fans that expel air either outside or into the roof space. [6] That wording is where a lot of this confusion starts, and a builder can point at an approved product list in good faith. It does not help you here. The VEU scheme is a retrofit incentive program for existing premises, not the compliance pathway for new building work, and it does not displace the NCC requirement. A VEU approved fan installed to a VEU approved outcome in a new dwelling still fails 10.8.2 if it discharges into the roof space.

Fixing it is usually cheap at this stage: a duct from the fan to an eave or roof vent, terminating at outdoor air, with the run-on timer and the door undercut confirmed at the same time. Doing it after the ceiling is closed up is not.