If you’re currently specifying commercial buildings in Australia and you haven’t reviewed your ventilation approach against NCC 2025, now’s the time. The updated code introduced a meaningful change to what’s required for natural ventilation in Class 5–9 buildings, and it has direct implications for how you design, specify, and get projects through certification.
Here’s a clear breakdown of what changed, what it means in practice, and where automated window systems come into the picture.
What the NCC 2025 Actually Says About Commercial Ventilation
Under NCC 2025 Part F6, Clause F6D7, commercial buildings, Class 5 (offices), 6 (retail), 7 (carparks/warehouses), 8 (factories), and 9 (public buildings including schools and hospitals) must provide openable area equivalent to at least 10% of the floor area served, if natural ventilation is the compliance pathway.
That’s double the previous requirement of 5%, which applied uniformly across all building classes under NCC 2022 and continues to apply to residential (Class 1–4) buildings.
A note on state adoption: NCC 2025 is not yet uniformly in effect across Australia. Victoria, the ACT and Western Australia adopted it from 1 May 2026. NSW and Queensland have deferred adoption until 1 May 2027 and are currently operating under NCC 2022, meaning the commercial openable area threshold in those states remains at 5% until then. If you’re working across state lines, confirm the operative code edition with your certifier before lodging.
For context under NCC 2025, a 500m² open-plan office floor would need a minimum of 50m² of openable window area to rely on natural ventilation under a DTS (Deemed-to-Satisfy) solution. In a typical commercial façade, that’s a significant design consideration, not something that happens by accident.
There are also practical depth limits that govern whether natural ventilation can work effectively, based on engineering principles rather than a specific NCC clause. Rooms relying on single-sided ventilation (windows on one wall only) are generally limited to around 2–2.5 times the ceiling height — roughly 5–7 metres from the façade for a typical commercial floor-to-ceiling height. Cross-ventilated spaces extend to around 4–5 times the ceiling height, or approximately 11–14 metres. If your floor plate goes beyond these limits, natural ventilation alone becomes physically ineffective regardless of how much openable area you provide, and your certifier will expect a different compliance pathway.
The Mixed-Mode Option, And Why It’s Gaining Traction
For deeper floor plates or buildings where full natural ventilation isn’t feasible, NCC 2025 allows a mixed-mode approach, a system that switches between natural and mechanical ventilation depending on conditions. When outdoor air quality and temperature are suitable, windows open and the mechanical system powers down. When conditions shift, the system closes and mechanical ventilation takes over.
This approach is gaining serious traction in Australian commercial design, and for good reason. When executed well, mixed-mode systems can reduce HVAC energy consumption by 20–40% compared to full mechanical systems in mild climates, a meaningful number on a Green Star or NABERS submission.
The compliance requirement here is important, and it catches some projects out: each mode must independently satisfy its respective standard. The natural ventilation pathway must meet F6D7 on its own. The mechanical pathway must meet AS 1668.2 on its own. You cannot use one to compensate for a shortfall in the other. This is where early-stage design integration matters — retrofitting compliance into a late-stage design is significantly more expensive than getting it right at schematic.
Where Automated Window Systems Come In
A 10% openable area requirement doesn’t just affect the glazing specification, it raises the question of how those windows operate, especially in buildings where occupants can’t reliably manage natural ventilation manually.
This is the core problem that automated window systems solve.
In a mixed-mode commercial building, window actuators work in conjunction with a Building Management System (BMS) to respond in real time to CO₂ sensors, temperature data, wind speed, and rain detection. Windows open when conditions are right. They close, and lock, when the mechanical system needs to take over, when it rains, or when a smoke or fire alarm is triggered.
That last point is critical. Smoke control is a separate compliance obligation under Australian building regulations, and automated window systems frequently serve a dual function: natural ventilation during normal operation, and smoke exhaust or make-up air during a fire event. When you specify window automation at design stage, you have the opportunity to integrate both functions into a single, coordinated system, rather than handling them as two separate problems late in the documentation phase.
Systems specified at design stage can also be sized, positioned, and programmed to meet both the F6D7 natural ventilation requirements and the smoke control requirements simultaneously. That’s harder, and more expensive, to achieve when automation is bolted on at construction stage.
What This Means for Specification
A few practical points worth having in your back pocket:
Involve your window automation consultant early. The 10% openable area requirement and the depth limitations for natural ventilation need to be worked out at massing and floor plate stage, not at design development. Once the building form is locked, your options narrow considerably.
Document your compliance pathway clearly. Whether you’re pursuing DTS via F6D7 or a Performance Solution for mixed-mode, your certifier will want to see how the natural ventilation path independently meets the standard. Actuator schedules, sensor integration, and BMS logic all form part of that documentation.
Don’t conflate ventilation and smoke control. They’re separate systems with separate standards (AS 1668.2 for ventilation, AS 1668.1 for smoke control), but a well-designed automated window system can satisfy both. Specify accordingly.
Check your climate zone. The viability of natural and mixed-mode ventilation varies significantly across Australia. What works beautifully in a temperate Melbourne office may not be appropriate for a north Queensland building without careful analysis.
The Bottom Line
NCC 2025’s 10% openable area requirement for commercial buildings isn’t a barrier to natural ventilation, it’s a specification challenge that automated systems are well placed to solve. The buildings that will meet it most elegantly are the ones where window automation, façade design, and BMS integration are considered together from day one.
If you’re working on a commercial project and want to understand how window automation fits your ventilation and smoke control compliance strategy, talk to us at design stage. It makes a significant difference to what’s achievable, and what it costs.
Blue Squared is a specialist window automation company working with architects, builders, and façade consultants on commercial projects across Australia. We supply and integrate automated window systems for natural ventilation and smoke control applications.
Category: Technical Education | Read time: 5 min | Tags: NCC 2025, natural ventilation, window automation, commercial buildings, Part F6
