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18, Jun 2018 -

The rise of eco-friendly wooden skyscrapers

The rise of eco-friendly wooden skyscrapers

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Wooden structures that don't use any concrete or steel are popping up all over the world, says CityLab contributor Amanda Kolson Hurley. For a long time the country moved away from building with wood because of issues like fire, but wooden towers have seen a resurgence as worries rise regarding the negative environmental impacts of cement production as well as the new features of engineered wood and Cross Laminated Timber (CLT).

Although U.S. building codes generally bar wooden structures more than 85 feet tall, the federal government has recently promoted research into building with wood, hoping to revive the domestic timber industry.

In Portland, Lever Architecture founder Thomas Robinson is working on an ambitious project: Framework, a 12-story mixed-use tower that will soon rise in Portland’s Pearl District. When it’s finished (likely in 2019), it will be the country’s tallest human-occupied all-wooden structure. Framework’s skeleton will be made of glue-laminated timber—pieces of lumber bonded together into massive beams and columns—while the walls and floors will be made of cross-laminated-timber (CLT) panels, in which layers of wood are stacked in alternating directions. Robinson’s team put both components through rigorous fire testing. A joined beam, column, and CLT panel were placed in a furnace, then weighed down with 25,000 pounds, to see how strong they would be after exposure to fire and heat. Two hours later, they emerged charred, but structurally intact. Mass timber doesn’t ignite easily—it’s more like a log than kindling. And the outer char layer that mass timber develops when burned actually insulates the wood.

Wood buildings are also environmentally friendly: The manufacture of concrete and steel accounts for an estimated 10 percent of greenhouse-gas emissions. Trees, however, are “carbon sinks”—they absorb and hold carbon until they decompose or are burned. According to a study in the Journal of Sustainable Forestry, substituting wood for other materials used in buildings and bridges could prevent 14 to 31 percent of global carbon emissions.

Source: Builder Online

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