Wood Skyscrapers: Mass Timber Frames Gaining Popularity

Study the evolution of tall buildings and you’ll see a trend from wood to stone (Gothic cathedrals). Stone then shifts to iron (Eiffel Tower), which advances to steel and concrete (Empire State Building and Burj Khalifa). Wood, which grows tall naturally, seems to get left behind.

However, the increasing popularity — and pragmatism, according to many designers and builders — of “mass timber” shows that wood, in its modern configuration, is a quadruple threat.

Suitable for commercial, municipal, and multi-family buildings up to 18 stories (depending on local codes) mass timber has measurably lower embodied energy and higher environmental paybacks. It’s quick to install, can be combined with traditional materials in hybrid buildings and it’s a design element.

But what is mass timber?

Oversimplifying it, think glue-laminated (glulam) beams, glulam posts and the world’s biggest plywood, cross laminated timber (CLT). Despite there being something of an alphabet soup of materials, the word “timber” in “mass timber” stems from the fact that the products — used both in vertical and horizontal structural applications — are made mainly from wood.

It’s the CLT panels that set mass timber apart

CLT panels are used as floor decks spanning up to 40 feet in 8-foot widths according to Kris Spickler, heavy timber specialist with Structurlam Products. Because the panels are glued together under pressure (like plywood) in three-, five-, and seven- layer assemblies, he noted, there are no nails to squeak and no subfloor or finished floor required. Plus they’re made from kiln dried, renewable lumber.

One of the environmental attractions of mass timber is that it can be made from regionally available resources. It’s typically derived from species like Douglas Fir in the Northwest — where tall wood buildings are gaining popularity among infill urban builders in Portland, Oregon, and college campuses in British Columbia — and Southern Yellow Pine in the Southeast. What’s more, trees grow back. Iron ore doesn’t.

From a design standpoint, structure is finished material for anything from walls (that can be factory-built with windows installed) to stairways. As a result, jobsite handling is different, and crew leaders should instruct carpenters not to walk on un-installed timbers, for example, said CLT expert John Boys, owner and president of Nicola Logworks.

From design element to money saver to renewable resource, mass timber stands tall for many builders.

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Mark Clement 

Photo Credit: MGA, Ema Peter.