What is the minimum outdoor air rate for offices in Australia?

AS 1668.2 requires a minimum of 10 litres per second (L/s) of outdoor air per person for office spaces. The rate must never drop below 0.35 L/s per square metre of floor area, even with demand control ventilation.

What does the NCC say about ventilation in commercial buildings?

NCC 2025 Part F6 requires all mechanically ventilated spaces to comply with AS 1668.2. It sets a CO2 verification limit of 850 ppm over 8 hours (Table F6V1). Part J6 also requires economy cycles for energy-efficient free cooling where cost-effective.

How much outdoor air does a 200 square metre office need?

For a 200 m² office with 20 people, you need 200 L/s of outdoor air (10 L/s per person). The area-based minimum is 70 L/s (200 m² × 0.35 L/s/m²). The per-person rate controls the design at full occupancy.

Is an economy cycle required under NCC Section J?

Yes. NCC 2025 J6D3(1)(c) requires outdoor air economy cycles where they can cost-effectively provide free cooling. Exceptions apply in climate zone 1 and spaces needing humidity control. The requirement applies per AHU, not per space.

What ventilation rate do I need for Green Star certification?

Green Star IEQ-1 awards points for providing 50% more outdoor air than AS 1668.2 requires. For offices, this means 15 L/s per person instead of the code minimum of 10 L/s per person.

Minimum Outdoor Air Rates for Commercial Offices

Section 1

What You Need to Know

Fresh air in offices keeps people healthy and meets the law. AS 1668.2 (the Australian Standard for building ventilation) sets the rules. For most offices, you need at least 10 litres per second (L/s) of outdoor air per person. Get it wrong, and your building will not pass certification.

Section 2

The Rules

Every office needs at least 10 L/s of outdoor air per person (AS 1668.2-2012, Table A1)
The outdoor air rate must never drop below 0.35 L/s per square metre of floor area, even with demand control (AS 1668.2-2012, Cl 3.3)
Indoor CO₂ must stay below 850 ppm over 8 hours (NCC 2025, Table F6V1)
All mechanical ventilation must comply with AS 1668.2 (NCC 2025, F6D6)
Economy cycles (free cooling with outdoor air) are required where cost-effective (NCC 2025, J6D3(1)(c)) — except in climate zone 1 or humidity-controlled spaces
Toilet and kitchen exhaust must go straight outside - no recirculation (AS 1668.2, Cl 3.5)

Section 3

What This Means in Practice

Take a typical 200 m² open-plan office with 20 people. At 10 L/s per person, you need 200 L/s of outdoor air. That is roughly the output of a small AHU (air handling unit). You will need ductwork from an outside air intake to the AHU, plus room in the ceiling void for the supply duct.

Now check the area-based minimum: 200 m² × 0.35 L/s/m² = 70 L/s. Since 200 L/s is well above 70 L/s, the per-person rate controls the design. But if the office is lightly occupied - say only 5 people - the per-person rate drops to 50 L/s. The area-based floor of 70 L/s then takes over. The BMS (building management system) needs to track this and adjust airflow using CO₂ sensors.

If the building sits near a busy road or loading dock, the outdoor air intake needs careful placement. Dirty air coming in defeats the purpose. Acoustic treatment on the intake duct may also be needed in noisy areas, which adds duct length and plant room space.

Section 4

Key Design Decisions

1

Fixed Minimum vs. Demand Control Ventilation

Use demand control ventilation (DCV) with CO₂ sensors in variable-occupancy spaces. The BMS adjusts outdoor air based on actual occupancy, saving energy while staying compliant.

Trade-off: CO₂ sensors and BMS programming add $500–1,500 per zone, but reduce energy costs by 10–30% on outdoor air conditioning.

2

Economy Cycle: Yes or No?

Install an economy cycle (free cooling with outdoor air) on each AHU where NCC Section J requires it. This lets the system use cool outdoor air instead of running the compressor.

Trade-off: Adds motorised dampers and controls (~$1,500–3,000 per AHU). Typically pays back within 2 years in climate zones 2–7.

3

Outdoor Air Intake Location

Place intakes away from exhausts, cooling towers, loading docks, and busy roads. The NCC and AS 1668.1 set minimum separation distances.

Trade-off: Good intake locations may conflict with the architect's facade design. Coordinate early to avoid late-stage redesigns.

4

Above-Minimum Rates for Green Star or WELL

Green Star IEQ-1 awards points for providing 50% more outdoor air than AS 1668.2 requires (15 L/s per person for offices). WELL Building Standard may require even higher rates.

Trade-off: Higher rates mean larger AHUs, bigger ducts, and more energy. Budget an extra $2–4/m² in HVAC capital cost.

Section 5

Who Needs to Know What

Section 6

References

AS 1668.2-2012, The use of ventilation and airconditioning in buildings — Part 2: Mechanical ventilation in buildings
AS 1668.2:2024, The use of ventilation and airconditioning in buildings — Part 2: Mechanical ventilation in buildings (updated edition)
National Construction Code 2022, Volume One, Part F6 — Light and ventilation
National Construction Code 2022, Volume One, Part J6 — Air-conditioning and ventilation
ASHRAE Standard 62.1-2022, Ventilation for Acceptable Indoor Air Quality (international reference)
Green Star - Design & As Built, IEQ-1 Ventilation Rates

Minimum Outdoor Air Rates for Commercial Offices

What You Need to Know

The Rules

What This Means in Practice

Key Design Decisions

Fixed Minimum vs. Demand Control Ventilation

Economy Cycle: Yes or No?

Outdoor Air Intake Location

Above-Minimum Rates for Green Star or WELL

Who Needs to Know What

Need this engineered for your project?

References

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