Demystifying Mass Timber

"In most U.S. cities, mass timber buildings, and specifically tall mass timber buildings, are a rarity, if they exist at all," Kira Barrett writes. But Sidewalk Labs' ambitious plan for a Toronto smart city called Quayside includes plans for ten of them. Barrett discusses the nature of the building material, which often consists of cross-laminated timber (CLT) panels, and its pros and cons.

To begin with the positives, proponents cite mass timber's capacity for carbon sequestration: one advocacy organization argues that a site with no building at all has a higher carbon footprint than one with a CLT structure. Mass timber buildings also weigh less than concrete and steel, reducing risk during seismic events.

But several factors hold mass timber back, the most obvious being the perception that wooden buildings are more prone to fire damage (even though engineered wood such as CLT mitigates some of that risk). There's also the question of access to timber for cities far from forests, the need to build out CLT production facilities, and a general lack of familiarity with the material on the part of architects and designers.

Its novelty means mass timber isn't included in the International Building Code, meaning that "construction with this material currently involves years of research, development and testing to make special state and city exceptions, on top of the already intensive construction process."