Why lodging providers need to pay attention to relative humidity

When I was a kid growing up in the very dry plains of Saskatchewan, Canada, my parents would put a humidifier in my room when I had a cold or the flu. I loved the soothing hum it made, which helped me fall asleep. I always thought that it was to make me feel better. However, many years later, when I started working in building design and on hospital projects, I realised the humidifier was to keep them from getting sick, not for me to get well.

It’s not common knowledge that viruses are airborne at below 40 per cent relative humidity. We all think that the cold and flu season passes in late spring and summer because the temperature is warmer. However, the end of flu season is likely to come because the air is more humid during the summer. In most countries, during the winter, heating the air dries it out to a humidity level closer to 20 per cent. Although these studies date back to the 1980s, they are particularly pertinent now.

In Canada, maintaining humidity levels is built right into the design requirements for a hospital. In this country, the requirement is that all operating rooms be maintained at above 40 per cent relative humidity at all times. Prior to co-founding Operto, a property automation system that provides intelligent control of smart home/IoT devices at scale for the short-term rental industry, I worked as a green building consultant.

The only other projects that I’ve looked at which maintain humidity levels [most buildings are only designed to maintain temperature levels] are laboratories and archives. For these spaces, keeping humidity at the ideal human comfort range [40-60 per cent] is also the ideal humidity level for most experiments, books and antiques being preserved and it stops viruses from being airborne.

Why is it then that most hospitality projects, like hotels and short-term rentals, don’t consider relative humidity as part of their essential operating basics?

But first, what is ‘relative humidity’ [RH]? It’s called relative humidity because it’s relative to temperature. If the RH were to reach 100per cent then it would be raining. With snow, we also know that the temperature can be very low and the relative humidity 100 per cent [this is obviously happening in the sky]. But it’s important to understand that it can be very cold outside but still very humid.

When I stayed at hotels across the Prairies in winter, I’d wake up in the morning feeling mummified. The air was so dry that I would have a dry mouth, cracked lips, and red eyes. As it was below freezing outside, the heating system keeping my room at 21 degrees Celsius, was pulling every drop of moisture out of the air, thereby impacting the RH. A friend told me his trick of leaving buckets of ice in the room to add to the moisture levels. Far less effective than a humidifier, but it’s a trick that I still use when I stay at a hotel or short-term rental that doesn’t have a humidifier.

So the big question is, if science tells us that people are more comfortable and that viruses are less present at between 40 per cent and 60 per cent relative humidity, why don’t more building types, including hotels and short-term rentals, design to meet this standard?

At home and in the Operto office we have always been very diligent in monitoring the RH to make sure it’s as close to 40 per cent as possible by running humidifiers. We use the same sensor that our hotel and property management clients use to monitor their properties to tell us, in the office, what the RH is [our Operto technology also measures temperature, noise and CO2 as well as RH]. Whilst CO2 is my biggest indoor air quality concern in summer, my biggest air quality concern in the winter has always been RH.

Now it really is time for more building operators and designers to pay attention to RH. It’s just too important for human comfort and wellbeing not to make this a priority.