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The Main Terminal at Portland International Airport (PDX), by ZGF Architects, sets a sky-high standard for air travel and heralds a new era of civic-scale mass-timber construction. What’s more, ZGF realized this daylit, tree-lined headhouse while partially adapting existing infrastructure and keeping the airport operational during construction. Perhaps the most striking element of PDX’s design is the modular 36-foot-high mass-timber roof, dotted with skylights and domes, and spanning some 9 acres. (PDX is also the first major airport in the United States to feature a mass-timber roof.) In total, some 3.5 million board feet—2 million for glue-laminated arches, 850,000 for mass-plywood panels, and 600,000 for a lattice made of dimensional lumber—were used to build the roof modules, largely without the need of specialized labor, due to the relative ease of connecting the components. All wood originated from within a 300-mile radius, and nonprofit Sustainable Northwest ensured that 73% of the roof’s timber was either FSC certified or could be traced back to family-managed businesses or tribal landowners that engaged in ecologically responsible forestry practices.