AS 1668.2:2024 Ventilation Rates Reference Guide for Australian Commercial Buildings
What You Need to Know
AS 1668.2:2024 is the Australian Standard for mechanical ventilation in buildings. The National Construction Code calls it up as a Deemed-to-Satisfy pathway. NCC 2025 calls up the 2024 edition, but NCC 2022 still calls up AS 1668.2-2012 incl. Amendments 1 and 2. NSW, QLD and SA stay on NCC 2022 until 1 May 2027. If you design, build, or certify a mechanically ventilated commercial building in Australia, the rates in this standard set your minimum.
The 2024 edition replaces AS 1668.2:2012. It keeps the per-person and per-area framework but tightens prescriptive values and updates several occupancy classes. See our complete AS 1668.2:2024 update guide for the full list of changes.
This memo gives the headline rates engineers and contractors use most, the rules that govern demand-controlled ventilation (DCV), and the compliance traps we see most often on real projects. For the complete occupancy schedule, refer to AS 1668.2:2024 Table A1.
Reference Table of Outdoor Air Rates
| Occupancy class | Per-person rate | Notes |
|---|---|---|
| Office (open plan, private, meeting rooms) | 10 L/s/person | Most common commercial rate |
| Retail (general) | 10 L/s/person | Sales floor space |
| Night clubs, ballrooms, games rooms | 15 L/s/person | Theatres and auditoriums are 10 L/s/person |
| Classroom | 10 to 12 L/s/person | 12 for students up to 16 years, 10 over 16 years |
| Hotel guest rooms | 10 L/s/person | Ensuite exhaust separate, 25 L/s minimum |
| Restaurant dining | 10 L/s/person | Kitchen handled separately |
| Childcare (Class 9b) | 12 L/s/person | No childcare row in Table A1. Designers adopt the classroom rate for up to 16 years |
| With particulate and odour filtration (Appendix D) | 2.5 L/s/person | 2012 occupancy minimum with treatment, not a DCV floor. 2024 sets 0.25 x the Table A1 rate |
Indicative reference based on industry-published values and CCC project use. Always confirm the exact figure in AS 1668.2:2024 Table A1 for your specific occupancy class.
Area-based floor for offices: outdoor air must never drop below 0.35 L/s per m2 of floor area. This applies even with DCV active (AS 1668.2 Cl 2.8.2 and 2.9.3).
For carparks, hospitals, kitchens, and laboratories, refer to the dedicated sections of AS 1668.2:2024. These spaces use different metrics (L/s per vehicle, ACHR, capture velocity) and are not on a per-person basis.
Key Changes from AS 1668.2:2012
Prescriptive Values Replace Performance Statements
Where 2012 used qualitative language for some provisions, 2024 sets numbers. This removes interpretation risk between consultancies and certifiers.
Two Calculation Methods
A simple per-person method for standard fitouts. A detailed method that accounts for occupancy profile and contaminant sources for complex buildings. Use the simple method by default. Reserve the detailed method where optimising airflow materially affects equipment sizing or energy.
Borrowed Ventilation Introduced
Outdoor air can be drawn from an adjacent compliant space under defined conditions. Useful for internal rooms that are difficult to duct directly. The source room must have surplus outdoor air available and the transfer path must meet the standard.
Carpark Tables Unchanged
The 2012 simple procedure already takes the greatest of 400 L/s per car space (times the usage factor), 2,000 L/s and 2.5 L/s per m2. The 2024 car park factor tables are unchanged. Check the 2024 flow equations in the standard before you plan smaller fans.
Healthcare Ventilation Rewritten
Infectious isolation room exhaust doubled from 6 to 12 ACHR. New HEPA filter requirements. New pressure categories for birthing suites and anaesthetic rooms. Healthcare projects in design need their ventilation schedules reviewed against the 2024 requirements.
Kitchen Exhaust Pathways Updated
Type B kitchen exhaust treated to Cl 3.10.4 now counts as objectionable only above 5,000 L/s, against 1,000 L/s untreated. Below that, the vertical discharge rule does not apply. In 2012, treated horizontal discharge was only a commentary concession.
Demand-Controlled Ventilation
DCV uses CO2 sensors to modulate outdoor airflow against actual occupancy. AS 1668.2 has allowed DCV since the 2012 edition. The 2024 edition retains this provision.
- The system must hold indoor CO2 below the design threshold. NCC 2025 Table F6V1 sets 850 ppm averaged over 8 hours (NCC 2025, Table F6V1)
- The outdoor airflow must never drop below the area-based floor (0.35 L/s/m2 for offices). DCV modulates between the area floor and the design peak (AS 1668.2, Cl 2.9.3)
- Equipment must be sized for the peak design occupancy. DCV reduces operating energy, not equipment size (standard engineering practice)
- NCC Section J now mandates DCV in high-occupancy spaces above defined outdoor airflow thresholds. Check Section J before deciding it is optional (NCC 2025, Section J)
Common Compliance Traps
- Ignoring the area-based floor. A lightly occupied office still needs the 0.35 L/s/m2 minimum. Headcount-only DCV will undershoot.
- AHU sized to the DCV minimum, not the peak. The fan and coil must handle full occupancy. DCV only turns down the airflow.
- Borrowed ventilation specified without checking the source room. The source must meet its own rate first and have surplus available.
- Healthcare projects still using 6 ACHR for isolation rooms. Equipment and ductwork need re-sizing for 12 ACHR.
- Assuming the 2024 edition cut carpark rates. The car park factor tables are unchanged. Check the flow equations before you downsize fans.
- Outdoor air intake placed near loading docks, exhaust louvres, kitchens, or busy roads. Compliance values mean nothing if the air entering the building is contaminated.
- Documentation issued under one edition, certification required under another. Lock in the edition with the certifier at the start of the project.
Who Needs to Know What
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References
- AS 1668.2:2024, The use of ventilation and airconditioning in buildings, Part 2: Mechanical ventilation in buildings, Standards Australia.
- AS 1668.2:2012, The use of ventilation and airconditioning in buildings, Part 2: Mechanical ventilation in buildings, Standards Australia.
- National Construction Code 2022, Volume One, Part F6 Light and ventilation, ABCB.
- National Construction Code 2025, Volume One, Section J Energy efficiency, ABCB.
- Standards Australia, Spotlight on AS 1668.2:2024 publication notice.
- AIRAH Ecolibrium Magazine, Celebrating AS 1668.2, Australia's misunderstood ventilation hero, August 2025.
- ASHRAE Standard 62.1-2022, Ventilation for Acceptable Indoor Air Quality (international comparator).