The Core Purpose of Make-Up Air: Make-up air replaces air removed by exhaust systems (kitchens, bathrooms, cleanrooms) to maintain pressure balance and prevent unconditioned air from being pulled through hidden gaps in the building envelope.
Design vs. Site Reality: Make-up air systems often fail on-site due to discrepancies between assumed envelope airtightness and actual as-built conditions, mid-project design revisions, and delayed commissioning.
Severe Compliance and Operational Costs: Pressure imbalance causes non-compliance with building standards (like NCC and AS/NZS ISO 9972), increases energy consumption, accelerates mechanical wear, and creates occupant discomfort (draughts, odours, slamming doors).
Diagnostics Require Context: Measuring pressure differential (e.g., air leakage at 50 Pa) provides a number, but understanding why a leak exists requires deep knowledge of the original design intent and building envelope details.
Integrated Strategy Beats Testing Alone: Achieving proper pressure balance requires connecting early-stage design strategy directly with handover verification, rather than treating testing as an isolated pass/fail exercise.
Make-up air exists to replace air removed by exhaust systems: kitchen extraction, bathroom fans, industrial ventilation, fume cupboards. Without it, a building pulls air from wherever it can find a gap: door undercuts, service penetrations, gaps in the envelope itself. That’s how a well-intentioned mechanical design quietly turns into an airtightness problem.
The goal on paper is simple: balance what leaves the building with what comes back in, at the right location, at the right pressure. The goal on site is a lot harder to hit.
A make-up air calculation is only as good as the envelope it assumes. If the drawings assume a certain level of airtightness and the as-built envelope leaks more (or less) than that assumption, the whole balance shifts. Dampers get value-engineered. Ducting routes change on site. A door schedule gets revised after the mechanical design was locked in. None of these show up as a “mechanical fault.”
They show up as a failed pressure diagnostic weeks or months later.
Every conduit run, switchboard penetration and cable entry through an external wall or ceiling is a potential leak path. Multiply that across a commercial fitout and the number of penetrations adds up fast.
Pipe penetrations for water, waste and gas all pass through the envelope somewhere, often through the same cavity as electrical and mechanical services, which makes sequencing and access harder to manage cleanly.
Fire-rated penetrations and collars have their own compliance requirements on top of airtightness, which means the sealing detail has to satisfy two standards at once, not just one.
Ductwork, louvres and plant penetrations are often the largest single openings in the envelope. A mechanical contractor who isn’t thinking about airtightness can undo the careful work of every other trade on the job.
Window-to-wall junctions, cladding interfaces and movement joints sit right at the edge of the air barrier. Get the membrane continuity wrong here and it’s one of the hardest defects to fix once the façade is closed up.
A standard build has some margin for a missed seal here or there. A Green Star target usually doesn’t. The performance threshold that earns the rating points leaves far less room for the kind of small, uncoordinated gaps that would barely register on a conventional project.
That means the coordination problem that exists on every job becomes a compliance risk on a Green Star job. It’s no longer just about comfort or energy bills, it’s about whether the rating is achievable at all.
Every trade matters, but coordination matters even more. A brilliant façade installer working next to an electrician who has never been briefed on the air barrier still ends up with a leaky building. The fix isn’t better individual trades, it’s getting everyone aligned on the same strategy before they start cutting into the envelope.
That’s exactly what trade workshops are for: getting every trade on the same page about where the air barrier is, why it matters, and what a compliant penetration actually looks like, before it becomes a defect that shows up at final testing.
Airtight buildings are built by teams, not individuals. No single trade can deliver a Green Star airtightness result on their own, and no amount of skill from one contractor can compensate for five others who were never briefed on the strategy.
Coordinate the trades early, using our 8-step airtightness process to keep everyone aligned from design through to final verification under AS/NZS ISO 9972, and the test at the end stops being a gamble. It becomes confirmation of work that was already done right.
If your project is heading toward a Green Star target, talk to us about coordinating your trades before the envelope closes up, not after.
Most commonly, a mismatch between the airtightness assumed in the mechanical design and the airtightness actually achieved on site, combined with commissioning sequencing that tests exhaust before make-up air is properly balanced.
Ductwork, louvres, window-to-wall junctions, and cladding interfaces represent some of the largest openings and perimeter joints in the envelope. Defects or membrane gaps at these locations are exceptionally difficult and costly to fix once the façade is closed up.
As early as possible – ideally during early design and pre-construction phase via trade workshops. Briefing trades on the air barrier strategy before they start cutting into the envelope prevents costly rework and defects later.
Find out which of these 10 details are leaking while they’re still cheap to fix. Book an appointment with Aerotight.
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