In This Issue
The Bridge: 50th Anniversary Issue
January 7, 2021 Volume 50 Issue S
This special issue celebrates the 50th year of publication of the NAE’s flagship quarterly with 50 essays looking forward to the next 50 years of innovation in engineering. How will engineering contribute in areas as diverse as space travel, fashion, lasers, solar energy, peace, vaccine development, and equity? The diverse authors and topics give readers much to think about!

Healthy Buildings in 2070

Monday, January 18, 2021

Author: Joseph G. Allen and John D. Macomber

Fifty years seems a very long time in the future for most industries. Not so in buildings and real estate; built structures routinely last decades if not hundreds of years, as long as they are economically competitive. Any discussion of the 50-year future has to consider existing stock as well as what’s being built new.

New Public Awareness

Some things do change. Four factors have recently emerged in the public awareness and will shape how the public and the industry consider healthy buildings:

  • People now have a vivid idea of what “public health” means in light of the covid-19 pandemic—the impacts of which are both more obvious and more immediately deadly than those of particulates or plastics.
  • Indoor air quality is clearly part of this equation. Until now, for the most part when people talked about air pollution they were referring to smog or other contaminants in outdoor air. But most people spend 90 percent of their time indoors (Allen and Macomber 2020a). Indoor air quality matters for health in general—as became clear during the pandemic—and levels of CO2, particulates, and volatile organic compounds directly affect human cognition as well (Allen et al. 2016).
  • Sensors and big data are personal and ubiquitous. A few years ago, a specialty hygienist had to be consulted to measure a few representative samples of air quality. Now dozens of inexpensive personal air quality monitors are available to give homeowners, renters, factory workers, or theatergoers real-time continuous readouts of air quality. These can be shared online and aggregated into reports that the public and others can use (Allen and Macomber 2020a).
  • Numerous physical perils threaten buildings, power grids, subways, and roads, such as riverine flooding, drought, sea level rise, wildfire … and pandemic. Every one of these makes it harder to keep a building and its occupants healthy.

Nine foundations of a healthy building.

FIGURE 1 Nine foundations of a healthy building.

These trends mean that engineers and designers will increasingly be asked to define a healthy building based on the health prospects of the occupants, not on the robustness of timbers, beams, and roofing. Our research indicates that there are nine foundations to a healthy building (figure 1; Allen et al. 2018).

Most of these are easy to detect. Although indoor air quality is the least well understood, most readers know they have spent unhappy time in stuffy hotel rooms, stale conference rooms, or stultifying classrooms. In the coming decades, as people are increasingly aware of the effects of bad indoor air and are equipped with personal air quality monitors, they will not tolerate it. This means that both new and existing buildings will need to invest in adaptations to be “more healthy”—and prove that the claim is true.

Measures and Controls

How can building health be measured and documented? Indicators of health performance (Allen and Macomber 2020a) can refer to the building’s engineering (ventilation) and to objectively measurable conditions (temperature, humidity, CO2, particulates). Others refer to the human users. Real-time indicators include biometric screening or subjective comfort surveys; lagging indicators include sick days for individuals and, increasingly important, retrospective healthcare costs for employers.

As we have advised building owners and managers about returning to work in the context of the covid-19 pandemic, benefit and cost should be balanced across a hierarchy of controls that also effectively balances risk (figure 2; Allen and Macomber 2020b).

The widest, most effective layer of the inverted pyramid is social isolation and quarantine. But it’s also the most costly in terms of disruption to business and society. Next is substitution of activities, in which only workers deemed essential return to the physical workplace, while many jobs are performed remotely or by proxies like personal grocery shoppers or even robots. Personal protective equipment, the cheapest approach in terms of capital cost, is the smallest component because it’s also less effective than the others (although often the most frequently deployed).

Two of the three middle “slices” will have the most impact both in coping with or recovering from the pandemic and in the buildings of the future. Administrative controls are what the office manager, landlord, or facilities manager decides about when or whether people come to work. Decisions about office density, how elevators are used, whether there is a salad bar, and management of queues and flows of people in and around a building arrived with covid-19 and will likely continue.

Engineering controls involve the physical infra-structure, things like air changes per hour, filtration efficiency, water quality, humidity, conveyances, windows. Because of the pandemic, they may now also include ultraviolet germicidal irradiation (UVGI) lights in duct-work or new HEPA-based filtration systems.

Engineering controls come at highly varying cost. It’s one thing to build a new house in the suburbs with stronger exhaust fans. It’s quite another to retrofit a high-rise downtown office with operable windows and associated HVAC upgrades when the structure was built to deliver a fixed minimum level of ventilation (that inadvertently compromised air circulation and quality).


This means that there are likely to be quite different strategies over the next 50 years that vary by both building type and location. Single-family homes are the most numerous building type in the world, whether custom made by a specialty builder or self-built in a slum or favela, and they are where people spend most of their time (in fact, people spend a full third of their life in one room, the bedroom). These dwellings may have multiple problems, so getting health right is critical in the residential sector.

In new buildings, it’s easier to engineer health into the core of the structure. Older cities in developed economies, however, may find that hundreds or thousands of existing structures need improvements that can’t be made simply by starting over.

Going Forward

The ideal is to design buildings to be healthy. This is driven by the current heightened awareness that buildings can spread disease—or help protect their occupants.

Hierarchy of controls to minimize risk in the workplace. PPE = personal protective equipment. Adapted from NIOSH (2015).

FIGURE 2 Hierarchy of controls to minimize risk in the workplace. PPE = personal protective equipment. Adapted from NIOSH (2015).

Market signals already indicate that companies are reevaluating their offices around health considerations, and some people are fleeing dense city apartments for more space in the suburbs. For apartment renters or condo buyers who have freedom of choice, for office tenants who are informed and thoughtful about the impact of indoor air quality on productivity, and for hotels, schools, conference centers, and hospitals, the ability to provide a healthy building will be a clear business differentiator, particularly in cities and regions of the world where the outside air is unhealthy.

Landlords, tenants, homeowners, renters, office workers, and students can all measure and share information about a building’s health performance in real time today. This democratization of information will lead to healthy building changes as revolutionary in this industry as mutual fund rankings were for the investment industry or user ratings for travel and restaurants.

Healthy buildings of 2070 will be assessed by the health of the people first, and the condition of the structure second. Good, healthy buildings will do well economically. Bad ones will decline in value or be abandoned.


Allen JG, Macomber JD. 2020a. Healthy Buildings: How Indoor Spaces Drive Performance and Productivity. Cambridge MA: Harvard University Press.

Allen JG, Macomber JD. 2020b. What makes an office building “healthy.” Harvard Business Review, Apr 29.

Allen JG, MacNaughton P, Satish U, Santanam S, Vallarino J, Spengler JD. 2016. Associations of cognitive function scores with carbon dioxide, ventilation, and volatile organic compound exposures in office workers: A controlled exposure study of green and conventional office environments. Environmental Health Perspectives 124(6):805–12.

Allen JG, Bernstein A, Cao X, Eitland ES, Flanigan S, Gokhale M, Goodman JM, Klager S, Klingensmith L, Laurent JGC, and 8 others. 2018. The 9 Foundations of a Healthy Building. Cambridge MA: Harvard Healthy Buildings Program.

NIOSH [National Institute of Occupational Safety and Health]. 2015. Hierarchy of controls. Online at

About the Author:Joseph Allen is an associate professor and director of the Healthy Buildings program at Harvard’s T.H. Chan of School of Public Health. John Macomber is a senior lecturer in finance at Harvard Business School.