Mass timber could elevate hospital construction

Picture a hospital and you might imagine concrete, stainless steel or plastic. But University of Oregon researchers hope to make wood — often overlooked in health care facilities — more commonplace in those settings.

Exposed wood, they’ve found, can resist microbial growth after it briefly gets wet. During their study, wood samples tested lower for levels of bacterial abundance than an empty plastic enclosure used as a control.

“People generally think of wood as unhygienic in a medical setting,” said assistant professor Mark Fretz, co-director of the UO’s Institute for Health in the Built Environment and principal investigator for the study. “But wood actually transfers microbes at a lower rate than other less porous materials such as stainless steel.”

Numerous studies support these properties of wood. A UO-led research team including scientists from the Salk Institute for Biological Studies and Portland State University wanted to explore what happens when wood gets wet then dries.

In a recent study published in Frontiers in Microbiomes, they shared their discoveries about the effects of moisture on surface microbes and volatile organic compound emissions from mass timber.

Mass timber is an engineered wood material emerging as a popular construction alternative in the U.S. But exposed wood is rarely used in health care facilities. That’s due in part to strict building codes that are slow to evolve, Fretz said. Another reason: widespread misperceptions about wood and pathogens.

“We wanted to explore how mass timber would stand up to the everyday rigors of health care settings,” said Gwynne Mhuireach, a UO research assistant professor. “In hospitals and clinics, germs are always present and surfaces occasionally get wet.”

For the experiment, blocks of cross-laminated timber were sealed in disinfected plastic boxes to create a micro-environment with carefully controlled temperature and humidity. To simulate a healthcare setting, air was filtered and exchanged at rates similar to hospital codes.

The team sprayed the blocks with tap water, inoculated them with a cocktail of microbes commonly found in hospitals, and took samples over a four-month period. An empty plastic box was used as a control.

The researchers compared coated and uncoated wood samples under three types of water spray events: just once, every day for a week and daily over four weeks.

The results of the study indicated wood is effective at inhibiting bacteria and revealed clues about wetting that will inform future research and development, Mhuireach said.

The empty plastic control box had greater viable microbial abundance than the wood samples, excluding the first 14 days after inoculation.

Wetting the wood blocks reduced the abundance of viable bacterial cells, with no discernable difference between coated and uncoated specimens. During wetting, microbial composition reflected what’s common in tap water more than the hospital pathogens the team introduced.

The experiments were the first to explore relationships between microbial communities on cross-laminated timber surfaces and the emission of volatile organic compounds, or VOCs, under dry and wetted conditions, Mhuireach said.

VOCs are chemicals that spread quickly in the air and are responsible for odors as diverse as perfume, mold or “new car smell.” Some present health hazards, but others are beneficial.

Wood can emit compounds called terpenes. Many smell pleasant and inhibit microbial growth. Mhuireach added there was a plateau in VOC emissions after wetting, which the team interpreted as a slight increase compared to an overall downward trend.

The study marks another milestone for the UO’s work to promote the use of mass timber in health care facilities.

That effort began in 2020 with funding from a Wood Innovations grant from the U.S. Department of Agriculture, Fretz said. That led to the formation of a focus group including architects, engineers and experts in health care building codes. Funding from the grant helped support this project.

Through his work with the TallWood Design Institute, a collaboration of the UO and Oregon State University, Fretz has been working to promote the production and use of mass timber, including materials manufactured in Oregon.

Construction using engineered wood produced from cross-laminated layers of veneer or lumber started in Europe during the mid-1990s and is growing in the U.S.

Stronger per pound than steel or concrete, mass timber boasts a smaller carbon footprint. Exposed wood also promotes health and healing, Fretz said, because it appeals to our inherent tendencies to connect with nature.

The benefits of that human trait, what architects and designers call biophilia, go beyond mere aesthetics.

Numerous studies link biophilic design to better health care outcomes, including shorter hospital stays, faster healing and mental wellness.

Wood’s ability to inhibit the spread of pathogens may stem from pores that trap bacteria or antimicrobial chemical compounds that occur naturally, Fretz said. It could also result from wood’s capacity to absorb moisture.

A respiratory virus shed indoors travels in a droplet of water. Wood will dry out that droplet faster than plastic or stainless steel, reducing virus survival time.

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