Healthy Indoor Spaces

Individuals in developed countries spend nearly 90% of their time in enclosed buildings ⁽⁵³⁾. With urbanization rates increasing, the global population spending more time indoors will increase further. Since the pandemic, awareness of hygiene and indoor air quality (IAQ) has grown, with a survey of 1,120 American workers showing widespread concern about the health impacts of poor IAQ ⁽⁵⁴⁾. This trend is further accelerated by post-pandemic health priorities, urban air pollution, and ESG strategies.

The pandemic and the shift to hybrid work models have increased attention on hygiene and IAQ in office and residential spaces. For instance, maintaining proper relative humidity levels between 40–60% is critical, as dry mucous membranes heighten infection risk and viruses survive longer on dry surfaces. Similarly, increased ventilation, reduced recirculation of indoor air, and improved air filtration can reduce sick leave from infectious diseases by 9–20% ⁽⁵⁵⁾.

As urban populations increase, so do the concentrations of air pollutants in cities. Today, 99% of the world’s population lives in places where air pollution exceeds WHO guideline limits ⁽⁵⁶⁾. In 2023, Delhi’s average particulate matter PM2.5 concentration exceeded the WHO guideline by over 20 times ⁽⁵⁷⁾. Both shortand long-term exposure to air pollution exacerbates health issues, increasing respiratory and cardiovascular diseases, healthcare costs, and mortality, with the WHO linking air pollution to 6.7 million premature deaths annually ⁽⁵⁶⁾.

Additionally, investors and tenants are increasingly integrating health metrics into their ESG strategies. While this contributes to broader societal benefits, it also delivers immediate advantages for investors and tenants. Investors see up to a 7.7% increase in rents for certified healthy buildings ⁽⁵⁸⁾, while tenants benefit from an 8% improvement in employee performance due to better IAQ ⁽⁵⁹⁾.

As demand for healthy indoor spaces grows, new buildings will increasingly prioritize occupant well-being, while existing structures will be retrofitted to meet these standards. Features such as thermal comfort, healthy indoor air quality, acoustic comfort, and optimal illumination will gain increasing relevance. High-quality sensors measuring and monitoring these parameters will become ubiquitous.

Thermal comfort is a key reason we have buildings. It plays a significant role in the way we experience spaces where we live and work. Six primary variables contribute to an occupant’s thermal comfort: dry bulb temperature, radiant temperature, relative humidity, air speed, metabolic rate, and clothing ⁽⁶⁰⁾. The first four variables can be controlled by the HVAC systems to provide occupants with a healthy and comfortable environment. However, today many buildings do not yet control these four variables properly.

Good IAQ supports health, well-being, and productivity. It is influenced by occupant respiration (CO₂, pathogens), outdoor pollutants (particulate matter, harmful gases), indoor emissions (volatile organic compounds), and foundation emissions (radon). Effective ventilation and advanced filtration are essential, yet many buildings still rely on manual window opening, which is inefficient for air quality and energy use.

Acoustic comfort is a key factor in creating a productive and satisfying built environment, as unwanted internal and external noise can disrupt work and relaxation. External noise has been linked to health risks like hypertension, stroke, and diabetes, while also increasing annoyance ⁽⁶¹⁾. Internally, noise from electronics, HVAC systems, and occupants can reduce concentration and productivity ⁽⁶¹⁾. To address these challenges, mitigating exterior noise, managing internal sound sources, and using sound-absorbing materials can enhance acoustic comfort.

Optimal illumination ensures visual comfort and reduces issues like eyestrain, headaches, and productivity losses. Beyond visual benefits, light significantly affects physiology by regulating the circadian rhythm, which controls alertness, digestion, and sleep. Improper lighting can disrupt this rhythm, leading to sleep disorders and higher risks of conditions like obesity, diabetes, and cardiovascular disease. To address this, buildings will increasingly adopt circadian lighting, glare control, automated shading, dimming, and daylight optimization ⁽⁶¹⁾.

Occupant well-being can also encompass more than just these environmental factors, such as drinking water purification, promoting healthy eating habits, encouraging physical activity, and supporting mental and emotional health through building design. Many of these aspects are addressed in today’s healthy building certifications, such as WELL.

Regulations also increasingly incorporate healthy indoor environment requirements. For example, the revised European Performance of Buildings Directive (EPBD) mandates that new non-residential zero-emission buildings, as well as those undergoing major renovations, where feasible, include measurement and control systems to monitor and control IAQ ⁽²⁸⁾.