Mechanical ventilation

Mechanical ventilation is powered air extraction or supply, exhaust fans, ducted systems, that meets the NCC’s ventilation requirement where a room cannot get enough natural ventilation through openable windows. It is the alternative to the 5%-openable-area natural-ventilation path.

The NCC gives a room two ways to satisfy ventilation:

• Natural ventilation: openable windows or doors with a combined openable area of at least 5% of the room’s floor area, opening to outdoor air.
• Mechanical ventilation: a powered system that moves a required air-change rate, used where the natural path cannot be met (an internal room with no external wall, a deep-plan layout, a basement).

Common cases on a build:

• Wet areas: bathrooms, laundries, and ensuites usually need mechanical exhaust (a fan ducted to outside) at a minimum flow rate, often interlocked to the light.
• Internal habitable rooms: a study or bedroom with no openable window to outside needs a compliant mechanical system to count as habitable.
• Range hoods and ducted systems: kitchen exhaust and whole-house systems sized to AS 1668.2.

For a builder the practical points are to identify rooms that cannot meet the 5% openable-area rule at the design stage and design in the mechanical system then, not patch it at occupancy, and to duct wet-area and kitchen exhaust to outside, not just into the roof space (a fan that dumps moist air into the roof creates a condensation and mould problem). Confirm the required flow rates and that the system is installed and ducted as designed, because ventilation is an occupancy-certificate check.

Also known as: Mechanical exhaust, powered ventilation, forced ventilation.

Category: Ventilation / NCC.

Related

• Openable area
• NCC ventilation and drainage

See also

• Thermal performance

References

• AS 1668.2 Ventilation and airconditioning, Standards Australia (verified 2026-06-02)

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Last updated: 2026-06-02. Verified: 2026-06-02. Quarterly review for currency.