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Video: Increasing winter humidity in buildings to reduce the spread of COVID-19

Design experts discuss engineering and architectural solutions for reducing transmission of COVID-19 by increasing relative humidity in buildings.

Interior relative humidity levels of at least 40 percent can substantially suppress all methods of COVID-19 spread, but especially airborne transmission. This is the science behind a March 2020 report from the Annual Review of Virology and the longtime research of Stephanie Taylor, M.D., a distinguished lecturer for the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). Yet most American buildings operate at much lower levels of humidity during the winter, usually 20 percent or less.

And simply adding humidifiers to raise the levels can cause catastrophic damage to the building’s walls, ceilings and floors, shrinking the lifespan of the building, increasing maintenance costs and energy consumption, and potentially causing mold, mildew and other health concerns. Sustainably raising winter humidity in buildings involves both architectural and engineering design. In this video, LEO A DALY design experts discuss current conditions and the design challenges for owners and operators who want to attain healthier levels of interior humidity to reduce the spread of COVID-19 and other illness.

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About the contributors:

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 and alternative delivery methods. Prior to spending the past 25 years in architecture leadership, Bill served as the assistant construction manager for the United States Holocaust Memorial Museum. Contact Bill at


Ellen Mitchell KozackChief 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. Contact Ellen at


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. Contact Kim at


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. Contact Tim at