Understanding Natural Ventilation Requirements

Whether you are designing a home or a commercial space, proper airflow is essential for health and comfort. Under the National Construction Code (NCC), there are specific rules for how rooms must be ventilated.

Rooms used by people must have ventilation, either by natural ventilation or by a mechanical ventilation or air-conditioning system complying with AS 1668.2 and AS/NZS 3666. If we are going with natural ventilation, we need to follow the requirements below.

Natural Ventilation Requirements

Natural ventilation must be provided through openable windows, doors, openings, or similar devices, with a total ventilating area of at least 5% of the floor area of the room being ventilated. These openings must lead directly to the outside air, such as:

1. A courtyard or space open to the sky.

2. An open verandah or carport.

3. An adjoining room

4. The Exception: This 5% rule does not apply to Class 8 electricity network substations.

Borrowed Ventilation

"Borrowed ventilation" is when a room gets its air from an adjoining room rather than a direct outside wall. Both rooms must be part of the same unit.

1. Requirements for Residential (Class 2, 3, and 4)

• Restriction: You cannot borrow ventilation for a sanitary compartment (toilet).

• Internal Opening: The opening between the two rooms must be at least 5% of the floor area of the inner room.

• External Opening: The window in the adjoining room must be at least 5% of the combined floor area of both rooms.

2. Requirements for Commercial (Class 5, 6, 7, 8, and 9)

• Internal Opening: The opening between rooms must be at least 10% of the floor area of the inner room.

• Height Limit: This opening must be measured no more than 3.6m above the floor.

• External Opening: The window in the adjoining room must be at least 10% of the combined floor area of both rooms.

Pro Tip: If a room receives air from a direct source and from an adjoining room, the percentages may be reduced proportionally.