The importance of make up air for Ventilation

A modern apartment, occupied for just over a year, already covered in mould and ghosting on the walls. No water leaks. No envelope failures. So what went wrong? In this episode I sit down with Andy to unpack one of the most common — and most misunderstood — problems in modern Australian apartment construction: airtight buildings without proper ventilation or makeup air. We walk through a real-world case study where intermittent bath fans, an oversized range hood, drying clothes indoors and zero continuous ventilation combined to create a perfect mould factory. When we ran the exhausts, the apartment was pulling 70 pascals of negative pressure. Andy mentions other apartments where he's measured up to 270 pascals — enough that you can barely close the front door. The problem isn't airtightness. Airtightness is good. Better facades, better fire separation, better acoustics, better weather performance — these are all wins. The problem is that the NCC's wording around continuous ventilation makes it effectively optional, and almost nobody is designing for the makeup air that an airtight building actually needs. Andy walks us through two pieces of hardware that solve the makeup air problem properly: A new high-volume makeup air unit with a double-dampener design — one dampener opens at low pressure to feed kitchen and bathroom exhausts, and a second closes off at around 25–30 pascals to stop wind ingress and gusts. Designed for the balcony or facade of class 2 apartments, age care and student accommodation. An advanced trickle vent system originally developed in Japan, with an acoustic insert, ember and insect protection, a 100 pascal wind dampener, and — the clever bit — a titanium-nickel bimetallic spring that automatically partially closes the vent below 18°C and fully opens it as the indoor air warms. It solves the single biggest reason occupants disable their trickle vents: cold draughts in winter. We also get into ASHRAE 62.2, AS 1668.2, the CSIRO airtightness research, why oversizing range hoods makes the problem worse, why door undercuts and grilles matter, and what a fabric-first approach actually unlocks for ventilation design. 00:00 Inside a mouldy 1-year-old apartment 01:43 70 pascals of suction: the makeup air problem 02:32 Why "natural ventilation compliance" isn't ventilation 03:36 AS 1668.2, 12 pascals — and the 270 pascal apartment 04:45 The new makeup air unit and double dampener system 06:55 Continuous vs intermittent: getting the balance right 08:37 Why exhaust fans keep getting oversized 09:44 Airtightness is good — we just need to add the rest 11:29 Trickle vents: lessons from New York, the UK and Japan 14:10 Inside the advanced trickle vent (acoustic, wind, ember) 15:25 The bimetallic spring that fixes cold-draught complaints 16:45 Pairing trickle vents with continuous exhaust 🛠️ Topics: makeup air, continuous ventilation, trickle vents, range hood depressurisation 🏢 Building types: class 2 apartments, age care, student accommodation 📋 Standards referenced: NCC 2019/2022, AS 1668.2, ASHRAE 62.2 👍 Like, subscribe and hit the bell for more building science deep dives. 🔧 Need a ventilation or airtightness consult? efficiencymatrix.com