About time: Damn right, mechanical ventilation is appropriate in all new buildings

17 December 2019 by Jason Quinn
Why am I sounding overjoyed at this simple text from BRANZ? The backstory goes a long way back.


In its <December 2019 Guideline https://www.branz.co.nz/guideline>, the front story is about smart vapour retarders (SVR) and how they lower the risk of mould in New Zealand wall assemblies. (There’s a story about that too, but that’s for another time.) The big deal is tucked up in the last two paragraphs.


“BRANZ recommends that appropriate ventilation of the building is essential, irrespective of whether an SVR is used or not. Data from our indoor air quality research suggests that a significant proportion of new buildings are underventilated, and simply having openable windows is not enough in a large number of these cases. In such situations, mechanical ventilation would be required to provide appropriate ventilation.


The overall approach is to build tight, ventilate right.”


So for the first time in writing—that I’m aware of—BRANZ is pointing out what most of us in the industry already know: that without mechanical ventilation, almost all new buildings are not ventilated sufficiently to keep the building structure free of mould. The exceptions are either where (1) there is very, very low internal moisture generation or (2) occupants diligently open windows several times a day (not just a quick airing in the morning).


All of which makes me recall a very loud argument in a pub with several prominent building scientists over the need for mechanical ventilation in every home. It was pretty heated, but other than pounding on the bar it didn’t become a punch-up. (Thinking back, I’m not so sure some of the argument wasn’t for the Socratic fun of it.)


But perhaps I didn’t argue my point far enough. Today I’d make it clear I mean every home, not just most, is in need of mechanical ventilation.


Most of all, I wish it hadn’t taken seven years for the argument to prevail. Fresh clean air—all the time—is not just a nice-to-have. Rather, building occupants have the right to expect it.

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