Is Passive House still relevant now that heat pumps are efficient and the grid is decarbonising? Nick Grant tackles this in a recent post, and while the energy arguments are sound, his take on ventilation is the real standout. The bottom line is that relying on “natural leakage” for fresh air is a public health hazard.
Grant identifies the only real argument against airtightness: saving developers a sliver of profit by skipping proper ventilation systems. The industry myth is that if a building leaks enough (say, over 5 ACH50), you can just slap in some trickle vents and cheap intermittent extract fans and call it a day and we see this in New Zealand and Australia every day.
This is dangerously wrong. I’ve been saying for years that if you can close the windows, you need continuous mechanical ventilation. Relying on random cracks means you are at the mercy of the wind. No wind? No fresh air.
Grant cites personal experience and academic research confirming that this “random leakage” strategy leads to poor air quality and serious health risks. It’s crazy to me that we still debate this. Once you accept that continuous mechanical ventilation is the only way to guarantee safe air, building tighter becomes the obvious choice for efficiency and comfort. It’s not about living in a sealed box; it’s about controlling the air you breathe rather than letting the building fabric filter it for you.
Abstract
Nick Grant’s article references two key studies demonstrating the failure of “natural” ventilation in modern homes. Farren et al. (2013) found that in modern dwellings relying on trickle vents, CO2 levels frequently exceeded healthy limits, posing risks to occupants. A 2023 Scottish Government report on ventilation guidance confirmed widespread non-compliance, finding that natural ventilation strategies failed to maintain adequate air quality and mechanical systems were often sub-optimal or disabled by noise-sensitive occupants.
Reference
Grant, N. (2025). Is Passivhaus Still Relevant?
Farren P, Howieson S, and Sharp T. Building tight – Ventilating right? How are new air tightness standards affecting indoor air quality in dwellings? August 2013 Building Services Engineering Research and Technology. Link
Building standards – ventilation guidance: research Published 3 May 2023, Directorate Local Government and Housing Directorate. Link ventilation guidance: research.