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White paper: Raising indoor humidity to reduce the spread of pathogens

Increasing indoor humidity reduces the spread of pathogens among other health benefits

White paper summary

Compelling new research such as from the Annual Review of Virology shows that relative humidity levels of at least 40 percent can substantially suppress transmission of COVID-19, and especially airborne transmission. Yet most American buildings operate at much lower levels of humidity during the winter — usually 20 percent or less.

In this whitepaper, we explore the research and look at why most buildings have low humidity in winter. We analyze solutions for building owners and operators who want to increase relative humidity to differentiate themselves, providing healthier spaces for occupants in the post-pandemic world. We evaluate mechanical systems needed to generate humidity and their energy costs, and we use LEO A DALY’s own Vapor Drive tool to demonstrate safe or unsafe building-enclosure performance at various levels of humidity in various climates. Finally, we discuss design solutions and retrofit options for buildings of all types.

Video: Designers discuss raising relative humidity in buildings to reduce transmission of COVID-19.


About the authors

Bill Kline, AIA, ACHA, EDAC, LEED AP, CAA, leads our Washington D.C. design studio as managing principal and is a vice president of LEO A DALY.. He has more than 30 years of experience leading design and construction projects for government, cultural, healthcare and educational institutions worldwide. A design advocate with a combination of depth and diversity of experience, he has special interests in sustainability, evidence-based design, alternative delivery methods and relative humidity in buildings. Prior to spending the past 25 years in architecture leadership, Bill served as the assistant construction manager for the United States Holocaust Memorial Museum.

Kim Cowman national director of engineeringNational Director of Engineering Kim Cowman, PE, LEED AP, HFDP, leads engineering across LEO A DALY. She is an expert in mechanical design for buildings. She has led design of precision mechanical infrastructure for large healthcare complexes and hospitals, and she has authored articles in Medical Construction & Design and Healthcare Design magazines. Kim serves on national committees for the American Society of Heating, Refrigerating and Air Conditioning Engineers. She is based in our Omaha studio.

Tim Duffy, AIA, CSI, LEED AP, is director of technical services for LEO A DALY. He is an expert in building performance. His understanding of building science helped lead design on recent high-profile projects such as the Heights Building and the North Terminal at Louis Armstrong New Orleans International Airport. He has more than 35 years of experience as an architect and is based in our Washington, D.C. studio.

Ellen Mitchell Kozack

Chief Sustainability Officer Ellen Mitchell-Kozack, AIA, LEED BD+C, WELL AP, SEED, leads sustainable design across LEO A DALY’s 10 design studios in North America and abroad. She develops the firm’s strategic initiatives in sustainable design worldwide, including Environmental, Social & Governance (ESG) principles, alignment with the UN Global Compact and Sustainable Development Goals, carbon footprint assessment and social impact. She is based in our Dallas studio.