AS 1668.2 Explained: Australia's Mechanical Ventilation Standard
What is AS 1668.2?
AS 1668.2 is the Australian Standard for mechanical ventilation in buildings. It sets the rules for outdoor air supply, contaminant exhaust, and how those airflows must be calculated, sized, and documented.
Most commercial buildings in Australia comply with AS 1668.2 by default. The National Construction Code (NCC) calls the standard up as the Deemed-to-Satisfy pathway for Part F6 (Light and ventilation). If a building has mechanical ventilation, the engineer either follows AS 1668.2 or produces a Performance Solution that demonstrates equivalent indoor air quality.
The current edition is AS 1668.2:2024, published in late 2024. It replaces AS 1668.2:2012, which is still cited by older NCC editions.
Where AS 1668.2 Fits in the Ventilation Standards Family
AS 1668 is a four-part standard. Each part covers a different aspect of how air moves through a building. Use this map to confirm AS 1668.2 is the right document for your project, or find the correct sibling part.
| Standard | What it covers | When you need it |
|---|---|---|
| AS 1668.1 | Fire and smoke control | Smoke exhaust, stair pressurisation, fire-mode HVAC |
| AS 1668.2 | Mechanical ventilation for indoor air quality | Most commercial buildings with HVAC |
| AS 1668.3 | Withdrawn (content moved into AS 1668.1) | Reference earlier projects only |
| AS 1668.4 | Natural ventilation | Naturally ventilated buildings under NCC F6 |
Where to look depends on the question. Smoke and fire engineering: AS 1668.1. Indoor air quality and exhaust: AS 1668.2. Natural ventilation: AS 1668.4.
What AS 1668.2 Covers
Outdoor Air Rates by Occupancy
The headline numbers most engineers reach for. AS 1668.2 sets minimum outdoor air rates for offices (10 L/s/person), retail, classrooms, hotels, restaurants, childcare, and dozens of other occupancy classes. The standard also imposes an area-based floor (0.35 L/s/m2 for offices) that must be maintained at all times. See our AS 1668.2:2024 ventilation rates guide for the full reference table.
Carpark Ventilation
Enclosed carparks need mechanical ventilation to manage carbon monoxide. AS 1668.2 sets the per-vehicle airflow, the area-based airflow, and the CO concentration limits that the system must control to. The 2024 edition reduced these rates to reflect modern low-emission vehicles. See our car park ventilation memo for the design rules.
Kitchen, Toilet, and Process Exhaust
Commercial kitchens (including dining), bathrooms, laundries, and a range of process spaces need contaminant-specific exhaust. AS 1668.2 sets the airflows, capture velocities, and discharge requirements. Type A and Type B kitchen hoods have separate rules. See our kitchen exhaust hood design memo for hood selection.
Healthcare Ventilation
Hospital isolation rooms, operating theatres, and treatment spaces have their own ventilation rules in AS 1668.2. The 2024 edition doubled isolation room air change rates from 6 to 12 ACHR and added new HEPA filter and pressure category requirements. Healthcare projects in design need their schedules reviewed against the 2024 baseline.
Demand-Controlled Ventilation (DCV)
Where occupancy varies (offices, function rooms, classrooms), CO2 sensors can modulate outdoor airflow against actual headcount. AS 1668.2 permits DCV. NCC 2025 Section J now mandates it in high-occupancy spaces above defined thresholds. The system must hold indoor CO2 below 850 ppm averaged over 8 hours.
Which Edition Applies to Your Building?
This is the question that causes the most rework on real projects. The applicable edition is fixed by the NCC edition under which the building is certified, not by the year of construction.
| NCC edition | AS 1668.2 edition called up | Status |
|---|---|---|
| NCC 2019 | AS 1668.2:2012 | Older buildings, retrofit context |
| NCC 2022 | AS 1668.2:2012 | Most current Australian projects |
| NCC 2025 | AS 1668.2:2024 | Active from 1 May 2025 |
Confirm the applicable edition with your private certifier or council in writing at project kickoff. Mid-project switches trigger re-design. The two editions are NOT interchangeable.
Carpark rates and healthcare schedules differ most between the two editions. If you have either system in the building, the edition matters for capital cost. See our AS 1668.2:2024 update guide for a side-by-side breakdown.
Most-Asked Questions
- Is AS 1668.2 mandatory? Yes, in practice. The NCC calls it up as the Deemed-to-Satisfy ventilation pathway. The alternative is a Performance Solution under Section A2, which costs more in engineering time and certifier review.
- Do I need an engineer to apply AS 1668.2? Yes for any project that needs council, CDC, or CC approval. Mechanical engineering documentation is normally certified by a registered Mechanical Engineer (NER, CPEng, or equivalent state registration).
- Can I buy AS 1668.2? Yes, from Standards Australia or Saiglobal. The 2024 edition is approximately A$420 for a single-user PDF.
- Does AS 1668.2 apply to residential buildings? Mostly no. Class 1 (houses) and Class 2 (apartments) typically rely on natural ventilation under AS 1668.4 or BCA F6 deemed-to-satisfy openable area rules. Communal areas, carparks, and commercial tenancies inside a Class 2 building still fall under AS 1668.2.
- What is the relationship between AS 1668.2 and ASHRAE 62.1? ASHRAE 62.1 is the equivalent US ventilation standard. The numbers are similar but not identical (US offices use 8.5 L/s/person, Australia uses 10). Documentation issued in Australia must be to AS 1668.2, not ASHRAE.
- Does AS 1668.2 require energy recovery? No, AS 1668.2 sets minimum airflow, not heat recovery. Energy recovery is mandated separately by NCC Section J for buildings above defined thresholds.
Three Compliance Traps We See Most
- Wrong edition cited. Documentation drafted to AS 1668.2:2012 lodged with a certifier requiring AS 1668.2:2024 (NCC 2025). Lock the edition in writing at kickoff.
- Outdoor air intake placed near a contaminant source. Loading docks, kitchen exhaust louvres, busy roads. The intake must meet separation distances regardless of how compliant the airflow rates are. See outdoor air intake separation distances.
- AHU sized to the DCV minimum, not the design peak. DCV reduces operating airflow, not equipment capacity. Sizing to the DCV floor leaves the building short of air during full occupancy.
Need AS 1668.2 mechanical engineering for your project?
Get a scoped fee proposal within 48 hours. CPEng qualified mechanical engineers. Registered in NSW, VIC, and QLD.
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.
- AS 1668.1:2015, The use of ventilation and airconditioning in buildings, Part 1: Fire and smoke control in buildings, Standards Australia.
- AS 1668.4:2012, The use of ventilation and airconditioning in buildings, Part 4: Natural ventilation of buildings, Standards Australia.
- National Construction Code 2025, Volume One, Part F6 Light and ventilation, ABCB.
- National Construction Code 2025, Volume One, Section J Energy efficiency, ABCB.