Wood construction: How does it stack up?
About 87% of the country's multifamily construction used wood framing in 2015, according to the U.S. Census Bureau. Builders used steel framing, wood's closest competitor, about 4% of the time, with concrete, concrete insulated forms and other framing methods making up the balance. Therefore, earlier this month, when the city council in Sandy Springs, GA, decided to ban wood construction more than three stories high and larger than 100,000 square feet as of Aug. 16, that curve ball took the industry by surprise, particularly since there has been an uptick in high-rise planning using all wood.
Cross-laminated timber (CLT) skyscrapers — or plyscrapers — are in the planning stages all over the world, from a 436-foot, 40-story tower in Stockholm Sweden, to an 80- story London high-rise almost 1,000 feet high. Proponents have said that these wood structures have the potential to fill an affordable housing gap in those urban centers and that they are more sustainable than their structural counterparts of steel and concrete. Getting ready to open in Minneapolis is what developers are calling "the first modern tall mass timber building" in the country, the seven-story T3. The U.S. Department of Agriculture even pushed the use of wood in construction last year through its sponsorship of the Tall Wood Building Competition in conjunction with the Softwood Lumber Board and Binational Softwood Lumber Council. Two winning teams, one from Portland, OR, and the other from New York City, were each awarded $1.5 million to help fund the development of their prize-winning designs. In addition, the USDA is backing wood as a viable material in the nonresidential sector to help boost employment in areas, mostly rural, that service the U.S. wood industry.
So when Sandy Springs officials said they were opting for noncombustible materials for the sake of safety, quality and longevity, as reported in the Atlanta Journal Constitution, were they signaling that they were on to something the rest of the industry wasn't, or did they get it wrong? As one can imagine, representatives from the wood, steel and concrete industries have a lot to say about that.
Wood vs. steel
"It's a very simple equation," said Kevin Lawlor, spokesman for the National Ready Mixed Concrete Association's Build with Strength initiative, in a press release following the decision. "The stronger the building materials you use, the safer occupants will be. The Sandy Springs Council set an example for the rest of the country."
However, no other municipalities that he knows of, said Ken Bland, vice president of codes and regulations at the American Wood Council, have excluded or are planning to exclude wood framing in such a manner. "It's hard to respond to Sandy Springs," he said, "since they really didn't provide any evidence that there are statistics to support the concerns with wood framing."
One of those concerns is fire safety. Wood buildings, as long as developers install fire sprinklers and build to code, Bland said, pose no more fire risk than any other type of construction. The major fire issue, however, said Rahim Zadeh, technical director for the Steel Stud Manufacturers Association,comes into play during construction, not after. The exposed wood, he said, creates a fire hazard that does not exist for steel-framed structures, with a small fire in just one part of the project potentially resulting in a total loss.
Human error, Bland said, such as welding that creates sparks or workers cooking in or near the building during construction, has been the culprit behind recent wood construction fires but said the AWC is trying to address those onsite missteps through an educational campaign at ConstructionFires.com. The program, Bland said, is intended to increase worker appreciation of the consequences of "being careless on the job site."
Durability and longevity are other concerns cited by the Sandy Springs City Council, but Bland said buildings constructed with concrete and steel — for reasons other than one would think — don't hold an advantage over wood when it comes to how long buildings typically stand. Studies that looked at demolition permits, he said, found that it was noncombustible buildings that were being demolished sooner than those that were wood-framed. In addition, he said, "The durability issue doesn't really make sense to us because we know, when properly detailed, (wood framing) will last as long as steel."
Replacing materials before they fail
In countries all over the world, said Dr. Thang Dao, Civil, assistant professor of civil, construction and environmental engineering at the University of Alabama, wood structures last hundreds of years. Most historical buildings, he said, are wood, and, as technology improves, we have ways of preserving those structures and treating wood to make it last longer. But, he said, the question of longevity begs the question: How long do we expect (the life of a building) to be? Chances are, he said, the structures, no matter the material, will be replaced before it fails.
In addition to fire control, Zadeh cited other advantages of using steel, like termite resistance and a straighter and more consistent framework, especially when it comes to installing sheetrock on metal studs. Sustainability is another area where steel outperforms wood, he said. "Steel is more green because of the high recycle content of steel studs," Zadeh added. And wood advocates, he said, never discuss the ramifications of harvesting wood and clear cutting. "They take that out of the equation to make their product look better," he said. "They leave out the major factor of clearing out a whole ecosystem."
Deforestation in the U.S., said Bland, is a nonstarter as, according to the AWC, twice as much wood is grown each year as opposed to what is harvested. In addition, according to a U.S. Forest Service 2010 Resources Planning Act Assessment, the total volume of trees growing in U.S. forests has increased 50% since the 1950s. Carbon sequestration, Bland said, in which the carbon dioxide is stored in the harvested wood, thereby reducing the amount released into the atmosphere, is another plus.
One thing on which Bland, Zadeh and Dao agree, however, is that steel and concrete are more expensive to install than wood. In fact, wood's affordability is one of the factors that has contributed to its popularity among those building en masse. Just a small increase in the per-unit cost is enough to curb development and make it cost-prohibitive, which in Sandy Springs, an area that has seen a population growth spurt during the last few years might be a welcome relief.
Nevertheless, Dao said, the city council is being short-sighted if its change in building codes is intended to make structures safer and last longer. "If we see a problem we try to fix it instead of ban it," Dao said. "That's what research is for."
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