(Bloomberg Businessweek) -- When the Gaia building at Singapore’s Nanyang Technological University opened last year, it was heralded as a revolutionary step toward a greener future. The massive structure—450,000 square feet—was constructed from sustainably harvested timber beams and panels. But these days, students and faculty are more focused on an unexpected downside: mold sprouting from all that wood. “It makes me feel a little grossed out,” says fourth-year student Grace Ng.
The problem highlights issues that can bedevil timber structures worldwide. While companies from Walmart Inc. to Microsoft Corp. have explored wood as a sustainable construction material, moldy timber in buildings has contributed to sickness, damage and legal battles from London to Melbourne.
Producing materials such as cement and steel is responsible for about 14% of global greenhouse gas emissions. Trees, by contrast, absorb carbon dioxide as they grow, and when their wood is used in construction, that carbon remains sequestered. The supplier of the wood for the S$125 million ($94 million) Gaia building says the structure stores more than 5,000 tons of CO2, after accounting for shipping.
But what looks good on paper has gotten a reality check in tropical Singapore, where it rains about 180 days a year. The wood in Gaia is primarily Austrian spruce, which was used to manufacture so-called mass-engineered timber—superthin layers glued into panels and beams that can be fashioned into columns, walls, roofs and more.
The trouble is spruce has a lower resistance to mold than many other species. In a place where relative humidity frequently reaches 80%, spruce that’s not properly treated is vulnerable to mold and rot, says Andrew Wong of the International Wood Culture Society. “It's basically a climate problem,” Wong says. “We’re in the tropics, and that requires special attention.”
But such problems aren’t confined to the tropics. Desert climates have huge variations in temperature, which can cause excessive expansion and contraction of wood, ultimately cracking it. In subzero climates, water can get into gaps and freeze, splitting timber elements. Engineers must take all of that into account when designing timber buildings, says Erik L’Heureux, associate professor of architecture at the National University of Singapore. “There are limitations and challenges to each climate,” he says.
Singapore has used mass-engineered timber in 20-plus projects in the past decade, and more than 30 companies there have begun or completed projects with it. Singapore officials, though, haven’t said whether other buildings are suffering mold problems.
Singapore’s colorful shophouses—two- and three-story colonial-era buildings with ornate plasterwork—feature beams made from hardwoods native to the region, which have a natural resistance to mold. But such wood is difficult to find and costs far more today than in the 1900s, when most of the shophouses were built.
Oil palm plantations have replaced many Southeast Asian forests, making chengal–the hardwood traditionally used in Singapore–scarce. And it’s ideally harvested after about a century, while spruce can reach maturity in a third as long. Hardwood is rarely used in big projects, because “it’s really expensive,” says Loh Kee Soon, a lead architect for Gaia at RSP Architects Planners & Engineers. To use such timber at scale, “you’d need a very large forest,” he says.
While the problems might have been mitigated by thicker protective coating, that was rejected out of cost considerations and to ensure the grain of the natural wood remained visible. Larch, a softwood with greater resistance to mold was an option, but it would have been pricier. So the project used spruce, with larch cladding on the columns most exposed to sun and rain.
There’s little argument about the aesthetic value of Gaia, which houses the university’s business school. The building’s 700-foot-long facade curves gently, its interior resembling a giant ski lodge bathed in natural light, with lush gardens tucked into internal courtyards. The ground floor is breezy and open, with no doors at the entrances.
More than a dozen conversations with students and staff who use the building, though, yield disgust, humor and concern about the problem. One staffer says he avoids his office because he’s afraid the mold will aggravate respiratory issues. “If the mold is just ugly, it’s not an issue,” says student Lifei Shan. “But since it can cause health problems, the school has to clean it up.”
The first thing visitors see and smell is the fragrant Austrian spruce that makes up the bulk of the building. Joey Feng, a mold inspector from a company called Air & Odor Management, isn’t impressed. Spotting white flecks that look like dust on a wooden pillar, Feng takes a sample with a swab and dips it into a clear liquid that turns lavender, indicating mold. She later finds more growth on air vents, which risks spreading it through the building. “I would treat this room immediately,” she says.
The school and architect Loh note that mold isn’t rare in humid Singapore, and they say it’s unlikely to affect structural integrity. Nonetheless, the school has developed “comprehensive” maintenance plans for Gaia, including reapplying sealant on the timber, adjusting the air-conditioning and asking staff to keep windows closed to reduce condensation. Experts in the field suggest treating surfaces with bleach, applying heavier coatings on the wood, installing dehumidifiers and running the AC 24/7, though that would make the building less sustainable.
“I can’t think of anywhere on Earth you could not use mass timber, if it’s designed for that particular climate,” says Art Schmon, an analyst at timber consultant Forest Economic Advisors. “The disadvantage is that it increases cost. Is it still competitive with steel and concrete? That’s a separate question.”
(Corrects details in 10th paragraph on parties involved in choosing construction materials)
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