All homes need mechanical ventilation Not just the “special” ones.

20 June 2023 by Jason Quinn

I was happy to see this lovely article on a very high-performance home down in Greymouth but I take issue with the last sentence, which implies that mechanical ventilation is needed because this house is special.

Yes, this home requires mechanical ventilation … but so do all homes in New Zealand that have windows you can close. That’s been known for 80 odd years and even BRANZ went on the record in 2019 to agree.

I live and work in an average 1970-build with the original aluminium windows. On a Welliington hillside right near the south coast so yes, it’s windy. And of course there’s air exchange even when the windows are closed because the building leaks air. But still CO2 will climb above 950 ppm if I’m working at home without windows open. 

Overnight it’s worse: two people (and a small dog) send CO2 to nearly 1400 ppm by morning and the windows are fogged on the inside from the relative humidity. I know, standard New Zealand lament. But even some of us with professional understanding of the importance of IAQ find it difficult to open windows to ventilate when there’s a 20 degree difference between indoor and outdoor air temperatures. Real time data from a reliable CO2 meter has however been a helpful prod.

New Zealand homes need continuous ventilation. Relying on occupants to open windows does not constitute a ventilation strategy.

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