A healthy building starts with better ventilation
For decades, we have failed to design our buildings with health as the primary focus. This is particularly true for ventilation standards that apply to homes, schools, offices, and just about everywhere else you spend time indoors, which specifically state that they are not intended to limit the spread of respiratory diseases. The COVID-19 pandemic — caused by a respiratory virus spread nearly entirely indoors — revealed the shortcomings of this approach.
For the first time in 40 years, we now have the opportunity to course correct.
ASHRAE, the professional engineering association that sets ventilation standards, has announced that it will release new health-based targets by June. Because ASHRAE recommendations ultimately inform building codes, this is a pivotal moment to reshape how we design and operate buildings. It’s critical that we get this right.
First, some background: The scientific record now reflects the reality that airborne transmission is the dominant mode of transmission for COVID, as for many other respiratory diseases. When we talk, sing, or simply breathe, we constantly emit respiratory particles. If we are infectious, those particles will contain the virus. Most of the virus is concentrated in particles less than five microns in size. (For reference, human hair is about 50-70 microns.) These fine particles will travel beyond six feet and accumulate indoors, unless they are diluted through ventilation or captured through filtration. All of this means that the way we design, operate, and manage our buildings has critical implications for reducing the spread of airborne respiratory diseases.
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Much of this was known early on in the pandemic, and many scientists and organizations issued calls for better filtration and enhanced ventilation. A key gap remained, though — while organizations called for more ventilation, few, if any, were willing to specify a ventilation target. ASHRAE did convene a team of scientists to propose targets in the winter of 2021, but their proposed targets were not published or released to the public.
The end result is that for the past three years, building owners and managers were told to do better when it came to ventilation, but were left on their own to determine what ventilation rates they should target.
I recently chaired the Lancet Covid-19 Commission Task Force on Safe Work, Safe School, and Safe Travel, which looked closely at ventilation targets. While there was debate about specifics, we all agreed that:
- Current ventilation targets are too low.
- Getting buildings off current minimums would lead to significant reduction in risk from SARS-CoV-2 and other respiratory viruses, like influenza.
- Higher ventilation and filtration rates come with multiple benefits beyond infectious disease, such as improved cognitive function and better math and reading test scores for kids in schools.
- While scientific inquiry into metrics and targets must continue, this should not impede us from recommending targets now.
Our recommendations covered three different ways building engineers typically think about ventilation: the amount of air supplied to the room per volume of the room, per person, and per floor area, using a “good, better, best” designation.
As example, and to give a sense of the numbers, a school should get three air changes per hour by design, but the reality is that it’s typical for a school to only get 1.5 air changes per hour as the system’s performance gets worse over time. A typical office might get even less, perhaps just one air change per hour. Our recommended standards are significantly higher: In both settings, we urge a new minimum of four air changes per hour, and a best practice setting of six or more.
In addition to releasing proposed targets, the Task Force published a separate report on approaches that every building owner or manager could take today to improve indoor air quality. Our strategies:
- Commission or recommission your building. This is the process of giving buildings a tune-up, much like we do for cars. Building system performance changes over time, and this process ensures the building is performing the way it was designed. This improves overall indoor air quality and saves energy and money; the return on investment for existing buildings is just a few years.
- Maximize outdoor air ventilation. Higher ventilation rates are associated with reduced disease transmission, fewer missed sick days, fewer missed school days, better cognitive function, and reductions in asthma.
- Upgrade filters to MERV13 or better. Buildings typically use MERV8 filters, which are designed to protect equipment and which capture about 50% of airborne particles. By contrast, MERV13 filters are designed to protect people and capture at least 80-90% of particles. Upgrading filters also helps to reduce outdoor pollution which penetrates into buildings, such as wildfire smoke. The cost to upgrade filtration from MERV8 to MERV13 works out to about $1.50 per month for a 5,000 square foot office, all-in: labor, filter material, energy.
- Supplement with the use of portable air cleaners, where necessary. In the event your existing building systems can’t hit these new health-based targets, there is a relatively low-cost and effective solution. A portable air cleaner with a HEPA filter can add several air changes per hour of clean air. Note that these devices need to be sized correctly for the room they’re in; you can use a simple tool from our Harvard Healthy Buildings program to help you find the right size.
These are not the only four strategies to consider. The Task Force report also discussed using air quality sensors that measure carbon dioxide (CO2) to verify ventilation performance; we built another tool to help you set a CO2 target if you go that route. Taken together, these strategies represent straightforward, feasible, cost-effective approaches that every building owner can pursue today.
The stakes are high: This is not just a health issue, but an equity issue.
While many well-resourced schools, universities, and companies have already adopted these enhanced ventilation and filtration strategies, the only way we can achieve clean indoor air for all is by codifying strong ventilation standards and making healthy building strategies the norm.
Healthy indoor air quality is a fundamental human right. It is imperative that leading engineering organizations like ASHRAE and public health agencies such as the Centers for Disease Control and Prevention, the World Health Organization, and the National Institute for Occupational Safety and Health create, adopt, and disseminate health-based standards for ventilation.
These organizations cannot continue to tell people to “bring in more air” without answering the critical question: “How much?”
Joseph G. Allen is an associate professor of exposure assessment science at the Harvard T.H. Chan School of Public Health.
Mary Delaware is the senior graphic designer at Harvard Public Health.