Ventilation in modular buildings is easy to overlook because you cannot see it in a finished room, yet it is one of the first things a Relevant Building Surveyor tests before signing off occupancy. Fresh air, moisture control and exhaust are health and amenity requirements under the National Construction Code, not optional extras. In factory-built construction the ventilation system splits across two places: some components such as bathroom exhaust fans, rangehoods and ducting are fitted inside the module at the factory, and the rest, the roof discharge points, the outdoor air intakes and the mechanical plant, are connected on site. This guide sets out how ventilation in modular buildings is designed, built and certified to NCC 2022 Part F6 and AS 1668.2, and who is responsible for each part in the Australian delivery chain.
Why ventilation is a compliance question, not a comfort one
It is tempting to treat ventilation as a comfort item, something a tenant fixes by opening a window. The Code does not see it that way. Part F6 sits in the Health and Amenity section of NCC Volume One because stale air, high carbon dioxide and trapped moisture are health issues. Poor ventilation drives condensation inside the wall build-up, mould on cold surfaces, and carbon dioxide levels that dull concentration in classrooms and childcare rooms. So the surveyor does not ask whether the room feels fresh. The surveyor asks whether the room was designed to a rule, and whether there is evidence the installed system meets it.
This matters more in a steel-framed module than in a loose site build, because a module is a sealed, well-insulated box. The airtightness that makes it energy efficient also means it will not leak its way to fresh air the way an old draughty building does. Ventilation has to be designed in, verified and documented. When that documentation is thin, the building can look finished and still fail its occupancy assessment.
The NCC framework: Part F6 light and ventilation
Under NCC Volume One, Part F6 covers light and ventilation together, and it offers two compliance routes. A room can be ventilated naturally, through permanent openings to outdoor air, or mechanically, through a system designed to AS 1668.2. The building class sets which classes of room and which spaces are in scope: apartments and residential buildings are Class 2, hotels and motels Class 3, and childcare, schools, health and aged care fall across Class 9. EcoPrestige supplies modules built to NCC Class 1a, 2, 3 and 9b compliance, but the applicable clause path still has to be confirmed for each project against the building class.
Clause references here follow NCC 2022. Victoria adopted NCC 2025 on 1 May 2026, while other states and territories transition on their own timetable, so the edition in force on the project has to be confirmed before design. The structure of Part F6 is stable across editions, but numbers and thresholds can move, which is exactly why a services engineer signs the design rather than a rule of thumb. For the wider compliance picture, see our modular building NCC 2022 compliance guide.
Natural ventilation: the 5% openable rule and where it breaks down
The natural ventilation route is the simple one on paper. A habitable room is treated as naturally ventilated when it has permanent openings, windows, doors or vents, with an openable area of not less than 5% of the floor area of the room, opening directly to outdoor air. Opening to an adjoining room or an enclosed corridor does not count unless that borrowed path also carries the openable area through to outside.
The problem is depth and reliability. Natural ventilation becomes weak roughly six to seven metres in from an external wall, so a deep floor plate, an internal room with no external wall, or a module buried in the middle of a stacked apartment or hotel layout cannot rely on it. And an openable window is only ventilation when someone opens it. In a childcare room or an aged care room, wind direction, security, insect screening and noise all make the window an unreliable sole supply. That is why so many modular projects in the target sectors move to a mechanical system even where a window technically satisfies the openable area.
Mechanical ventilation to AS 1668.2
Where natural ventilation cannot be achieved, or where the space type demands it, the system is designed and installed to AS 1668.2, the mechanical ventilation standard. Several spaces effectively always need mechanical treatment: bathrooms, sanitary compartments and laundries need exhaust to remove moisture and odour, kitchens need exhaust and grease filtration where cooking occurs, internal rooms with no external wall need supply and exhaust, and enclosed carparks need a system sized for carbon monoxide control.
AS 1668.2 sets outdoor air rates by use. As a guide, offices are around 10 litres per second per person with a floor-area minimum, retail similar, and classrooms higher at about 12 litres per second per person. Both the per-person rate and the per-area rate apply, and the larger airflow governs. Exhaust from wet areas and kitchens must discharge to outside, never into a ceiling void or roof cavity, because dumping moist air into the cavity is a direct path to the condensation and corrosion problems the rest of the Code is trying to prevent.
Childcare, aged care and apartments: why these sectors push to mechanical
The sectors EcoPrestige builds for are the ones where ventilation is scrutinised hardest. For a childcare centre, AS 1668.2 points to about 12 litres per second per person of outdoor air, counted across children and staff, so a room licensed for twenty children and four staff is sized for twenty-four people. Guidance for these rooms also targets carbon dioxide well below roughly 850 parts per million above the outdoor level, which is why demand-controlled ventilation with carbon dioxide sensors is common in playrooms. Nappy change and sanitary areas need dedicated exhaust running continuously through occupied hours to hold them at negative pressure so odours do not migrate into playrooms. Our modular childcare centres guide covers how these rooms are planned.
The same logic drives modular aged care buildings and modular apartment construction, where internal bathrooms, kitchenettes and deep plans mean mechanical exhaust and outdoor air are designed in from the module layout stage. Getting the intake and discharge points onto the module drawings early is what keeps the on-site connection clean.
How ventilation ties into condensation and energy
Ventilation does not stand alone. It is the release valve for moisture, so it is read alongside condensation management and the energy provisions. Too little ventilation traps water vapour against cold steel and plasterboard, which is the failure mode covered in our note on condensation management in steel-framed modular buildings. Too much uncontrolled air movement wastes conditioned air and undermines the thermal performance set out in the energy efficiency provisions, where NCC Part J6 governs air-conditioning and ventilation for larger buildings. A good design balances the two: enough fresh air and exhaust to satisfy Part F6, delivered efficiently enough to satisfy the energy path.
What splits between the factory and the site
In a modular delivery the ventilation system is a shared build. Inside the module, the factory typically installs exhaust fans, rangehoods, in-wall and in-ceiling ducting, grilles and the penetrations through the module envelope, all documented in the shop drawings. On site, the head contractor connects the roof or wall discharge terminations, links modules where a duct crosses a module join, installs any central mechanical plant, and commissions the system. The join between the two is the point to document, because a duct that stops at the module edge and is never connected on site is a defect that a finished ceiling will hide.
Who certifies ventilation, and the evidence a surveyor asks for
The ventilation design and its certification to AS 1668.2 sit with the project’s mechanical services engineer, and the licensed head contractor or registered building practitioner coordinates it as builder of record. EcoPrestige supplies the modules with their factory-fitted ventilation components and the design evidence for that scope; the installed and commissioned system is certified through the head contractor’s chain, and the occupancy certificate follows from that evidence. A surveyor will typically ask for the mechanical services design and calculations to AS 1668.2, the schedule of fans and airflow rates, a commissioning report showing measured airflows against design, and confirmation that wet-area and kitchen exhausts discharge to outside. Agreeing this evidence list before manufacture is what avoids a rework argument at occupancy.
Ventilation in modular buildings is not harder than in a site build. It is simply documented differently, because the work is shared between a factory and a site. Design it against the correct building class, decide natural or mechanical honestly rather than hopefully, keep wet-area and kitchen exhaust discharging outside, and hold a commissioning record at the end. Do that and the fresh air you cannot see becomes the evidence a surveyor can.