How does COVID-19 spread? 

  • Close contact transmission through large droplets (> 10 microns), which are released and fall to surfaces less than about 6ft from the infected person.
  • Airborne transmission through small particles (< 5 microns), which may stay airborne for hours and can be transported long distances.


How does air move in a building?

  • Air flow patterns in buildings are the result of combined forces such as wind, the stack effect or called chimney effect [3], distribution systems and ventilation mechanisms. (Graphic of air flow in a building)

What are the common issues and how can we prevent the spread of COVID-19 in buildings?

  • Most single or two-family homes (SF) homes do not have ways to regulate outdoor air intake through HVAC systems, and as a result have to rely on operable windows to bring in outdoor air in buildings that helps dilute airborne contaminants, making infection less likely.
  • Commercial and common areas of large multi-family buildings typically recirculate some air. This has been proven to lead to higher risk of infection during outbreaks, as contaminated air in one area is circulated to other parts of the building (as it did in the school with measles).

What should we be doing?

  • First, bringing in more outdoor air in buildings with heating and ventilation systems (or opening windows in buildings that don’t have these systems) helps dilute airborne contaminants, making infection less likely. For years, we have been doing the opposite: sealing our windows shut and recirculating air. (Graphic of open windows)
  • In relation to buildings with dedicated ventilation systems (not mechanical ventilation), it is recommended to switch on ventilation systems a couple of hours earlier and to extend the operation.
  • A 40% to 60% relative humidity may be ideal to reduce viral transmission and infection in general, and increasing evidence indicates that higher relative humidity has been shown to reduce infectious influenza virus in simulated coughs

What’s the link to COVID-19 mortality in the worst affected areas?

  • We knew that COVID-19 adversely affects patients with pre-existing conditions. We now are aware that patients in areas that had high levels of air pollution before the pandemic are more likely to die from the infection than patients in cleaner parts of the country, according to a new nationwide study that offers the first clear link between long-term exposure to pollution and COVID-19 death rates. The results suggest that long-term exposure to air pollution increases vulnerability to experiencing the most severe Covid-19 outcomes. The burden of air pollution is not evenly shared. Poorer people and some racial and ethnic groups are among those who often face higher exposure to pollutants and who may experience greater responses to such pollution[6]. There is also a greater risk of particle pollution coming from traffic sources where residential segregation based on housing market dynamics and land costs has led to aforementioned groups witnessing higher rates of: asthma attacks in children and the onset of childhood asthma, impaired lung function, premature death and death from cardiovascular diseases and cardiovascular morbidity

Who are the key stakeholders here and what can they do?

  • Government agencies, real estate companies and portfolios, landlords, tenants, construction managers, engineers, architects and various community organizations that own/operate/maintain/live/engage in the built environment.
  • From a policy standpoint, utilities and municipalities can advance health and well-being by enacting local laws that promote healthy building standards and best practices.

Additional Resources

The safety of our employees, contractors and customers is our overriding priority. As the pandemic continues, we are monitoring the situation closely and following the guidance from the Centers for Disease Control and Prevention and local health authorities. Below is a set of relevant resources: