Can Building Science Help Reduce the Risk of COVID-19?

CC BY 2.0. HRV and CO2 hot water heater in a Passive House near Seattle/ Lloyd Alter

Yes, but not necessarily in the way you think.

When I am not writing for TreeHugger, I am teaching Sustainable Design at Ryerson University, and talk a lot about the Passive House standard, which focuses primarily on reducing energy consumption through insulation, airtight construction and minimizing thermal bridging, with a side of mechanical ventilation with heat recovery. I wondered if that ventilation system would make a difference in reducing transmission of the COVID-19 virus. I also wondered if HEPA filters would help.

Do HEPA filters capture the virus?

HEPA filter effectiveness

HEPA filter effectiveness/ NASA/Public DomainThe first question was whether HEPA filters actually can capture the COVID-19 virus and the tentative answer is yes, sort of. Tim Hefferman of the Wirecutter points to a NASA study which shows the .01 micron virus being captured at a very high rate of efficiency, upwards of 99 percent.

The problem is that the viruses probably never get to the filter. As Hefferman notes, the current consensus is that it is not an airborne virus.

Rather, experts believe that the coronavirus is transmitted by person-to-person contact and by contact with virus-laden droplets expelled by an infected person’s coughing and sneezing. Coughs and sneezes certainly suggest “airborne” to most people, but such droplets travel only about 6 feet before falling out of the air and settling on surfaces.

Hefferman concludes that "as far as researchers know now, air is not the vector by which the virus spreads, and that air purifiers should not be considered protective."

Is the virus airborne?

But another more recent study out of UCLA found that the virus can stay floating in the air. The author of the not-yet -released study tells NPR that "the virus can survive up to 72 hours on stainless steel and plastic surfaces and on cardboard up to 24 hours," and also that "the virus can remain viable floating in the air for some number of hours. The experiments went out to three hours, and, you know, there were still viable viruses present." So ventilation could become very important.

Ben with HRV

Ben with HRV in Garage/ Lloyd Alter/CC BY 2.0

Another important point is that in a Passivhaus building, the interior air is not filtered and recirculated, as it is in normal homes; it is exhausted and replaced with fresh outside air through the Heat Recovery Ventilator, as in Ben's house. Because they are not recirculating the air, they do not need HEPA filters, which add a lot of flow restriction and would need more power. The filter on the HRV might clean the outside air of pollen and dust but not COVID-19 if someone happens to be coughing into your air intake. But if you live in a place with recirculated air, that HEPA filter might help.

What about apartments?

CC BY 2.0. The Heights/ Lloyd Alter

The Heights/ Lloyd Alter/CC BY 2.0

In a multifamily building, it is a very different story. Traditional apartment buildings in North America have pressurized corridors so that smells of cigarette smoke do not travel through the corridor from one unit to the other. "Fresh" air for the apartment usually enters under the suite door, along with dust and pollen and anything else tracked in by people and dogs in the corridor. It's then exhausted, usually through the bathroom. So if someone coughs outside your door, does it get through?

HRV closet

HRV closet/ Lloyd Alter/CC BY 2.0

Modern higher quality apartments and Passivhaus apartments have separate mechanical ventilation systems for each unit and gasketed doors to the corridor. Even when Passivhaus buildings have shared systems, like the one in Vancouver shown above, it is always fresh air supplied through ducts, not through the corridor, and it is not recirculated.

If you live in an older building without its own fresh air supply, now that spring is here, crack open the window a bit so that the air comes from the outside instead of the corridor, unless you live on top of some highway.

Alison Bailes points to an article by Kristof Irwin in Positive Energy, who writes:

Ventilation is crucial. Bringing in more filtered outdoor air in buildings heating/cooling systems (or opening windows in buildings that don’t) helps extract airborne contaminants from the building, making infection less likely. For years, we have been doing the opposite: sealing our windows shut and recirculating air. Just look at the residential code requirements for ventilation (or even scarier, look at the enforcement). The result are homes, schools, and office buildings that are chronically under-ventilated. This not only gives a boost to disease transmission, including common scourges like the norovirus or the common flu, but can also significantly impair cognitive function. If you don’t have mechanical ventilation in your home, make yourself a calendar reminder to open up the windows a few times per day/evening (whenever you’re home) for as long as you can. Obviously, depending on your climate this may prove difficult for thermal comfort or humidity introduction into your space, but still generally a good idea.

But the real issue is the humidity.

desired humidity

© Recommended humidity/ASHRAE

As the weather gets warmer this is less of a problem, but there is lots of research that keeping the humidity between 35 percent and 55 percent reduces transmission of viruses; as Peter Yost of Green Building Advisor notes, "The higher the RH the more quickly the virus falls to the floor." Elrond Burrell points us to research by Doctor and Architect Stephanie H. Taylor that was written about flu transmission but is probably relevant:

Research continues to reveal that dry indoor air is connected to MORE infections in people. This helps explain why the flu season is in the winter, when cold outdoor air - already low in moisture, is brought inside and further dried out when warmed. The obvious solution is to provide indoor humidification to achieve a beneficial relative humidity (RH) level between 40 to 60%. Interestingly, this is already done in animal research laboratories where replacing test subjects that died from seasonal respiratory diseases is costly and could skew the project data.
humidity's effect on viruses

© Stephanie H. Taylor

This is where building science and the Passivhaus standard comes into play. Dr. Taylor continues:

Opponents to indoor humidification, usually building professionals, understandably worry about condensation problems when the outdoor temperature is low. This is a valid concern that needs to be addressed by avoiding thermal channels in walls and ducts.

In super-insulated buildings like those built to the Passivhaus standards, the walls and even the windows are pretty much the same temperatures as the indoor air, so there is no fear of condensation, mold or bacteria growth. It becomes easy to hold the humidity in the desired range.

There are other benefits; because the walls are room temperature, one doesn't lose or gain heat from them or the windows, so the occupant is much more comfortable. They are quieter, which is nice when you are sick. You don't have to pay much to heat or cool them, which is nice when you have no income.

Architect and Passivhaus expert Bronwyn Barry summed all the points up:

The non-recirculating air is really the best benefit. I’m betting Direct exhaust from wet rooms & fresh supply to living spaces is going to become an essential feature of EVERY building. I’m also thinking that we need to now properly evaluate all other health-related aspects of buildings. Mold from interior window condensation is huge. However, the resilience aspect of Passivhaus is truly the real winner here.

Healthy interiors, too!

chair ad

Thonet Chair ad/via

I will again make my case for modernist minimalism, noting that the COVID-19 virus "can survive up to 72 hours on stainless steel and plastic surfaces "and that we should ensure that the stuff we bring into our houses is easily cleaned. That's why the modernists designed all that tubular and plywood furniture; as Mies van der Rohe noted about modern design, and his chairs in particular,

It therefore promotes comfortable, practical living. It facilitates the cleaning of rooms and avoids inaccessible dusty corners. It offers no hiding place for dust and insects and therefore there is no furniture that meets modern sanitary demands better than tubular-steel furniture.

Keep it simple and keep it healthy.