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The Engineer: Condensation and the coronavirus

When clients replace older, leaky curtainwall systems with a new, tighter system, they call us complaining of water droplets on the inside pane of glass.

June 12, 2020
By David Heska


I hope that all of our Glass Canada readers are safe and healthy during this unique time. Everyone is talking about the coronavirus so I figured that I might as well jump on the bandwagon and address a recent article from the Globe and Mail. In the article they asked a question about how humidity might impact the transmission of the virus. According to the article, there was some evidence that the virus may not live as long or transmit as readily in air with higher relative humidity. So will warmer and humid summer weather cause the spread of the virus to slow? Is there evidence to show that COVID-19 has spread more in countries with colder climates? I will leave the answers to those questions to scientists and medical professionals. What I want to dive into here is glass, facades, and Building Science 101. My colleague, Alex McGowan, joined Patrick Flannery for Glass Talk Episode #9 last month to discuss this very topic, so here’s a crash course.These issues might gain extra relevance if humidity is indeed found to have an effect on infectious disease spread.

Here are a few statements from the Globe and Mail article. “Most Canadian buildings are advised to maintain humidity levels between 35 and 55 per cent…In older buildings it’s difficult to sustain those levels” and “less than five per cent of buildings currently comply with ASHRAE’s standard.”

The first statement is true, and although I have not read the report about the number of buildings meeting the ASHRAE standard I do believe it’s less than five percent.You may be asking, what does that mean and why should I care? Here’s the answer: There are two ASHRAE standards that discuss humidity. The first is ASHRAE Standard 55 “Thermal Environmental Conditions for Human Occupancy” which considers occupant comfort and appropriate temperatures. The second is ASHRAE Standard 62 “Ventilation for Acceptable Indoor Air Quality” (which is split into two parts for commercial and residential buildings). The newspaper article took the stunning, low, five per cent number and presented it in such a way that readers might think “What are we doing wrong?” Well, guess what? Most buildings in Canada have not been required to comply with these ASHRAE standards. Buildings are “advised” to maintain humidity between 35 and 55 per cent, but other than occupant complaints, nothing will happen if the humidity in buildings falls below this range. And here in Canada, with our months of cold, dry Arctic air and forced-air furnaces blasting away, getting indoor humidity levels up is often seen as more trouble than it’s worth.


Increasing humidity levels in buildings is not just as easy as making a few HVAC adjustments. The study of building science looks at the interaction of the building façade with all of the other components in the building.This is why when clients replace older, leaky curtainwall systems with a new, tighter system they call us complaining of water droplets or frost collecting on the inside pane of glass.The humidity in the room has not changed, but the pathway for moist air to escape has been blocked. Now when this humid air meets the cold surface of glass, condensation appears and complaints follow.

I will close with a couple of recommendations. As buildings become tighter, designers and manufacturers need to work together in order to be able to properly add and remove humidity. One solution on the HVAC side is the use of heat recovery ventilation systems. One solution on the glass and façade side is the use of more operable windows. The old adage still stands: “Build tight.Ventilate right.”