The first cross-laminated timber (CLT) building in the U.S. — a four-storey, 92-room “blast resistant” hotel for military personnel in Alabama — has sold builder Jeff Morrow on the advantages of the pre-engineered wood product.
It typically takes 14 to 20 weeks using a crew of 40 to 50 to frame a hotel of that size, says Morrow, but by using CLT instead the job was completed in 10 weeks with a crew of only 10 and a mobile crane.
"We’re finding that CLT is completely but positively disrupting the way we design and build our buildings," Morrow told an audience of builders, architects and engineers at a seminar titled More with Less: Building With Cross Laminated Timber, presented at the Toronto Wood Solutions Fair recently.
Morrow is the program manager of the Timber & Innovations Group of Lend Lease (US) Public Partnerships LLC, which erected its first building using CLT in Australia seven years ago.
Calling CLT "plywood on steroids," he says there are several reasons why a builder might choose it over traditional steel and concrete construction, including lower labour costs and speed of construction.
Poor soil conditions is another reason.
"CLT can have about a fourth of the weight of cast-in-place concrete," he says, noting that can substantially reduce the soil remediation costs required for a foundation.
Morrow says constructing with CLT is not difficult. While the first three-storey tall stair shaft at the Alabama hotel took his crew 13 hours, only seven hours was required to complete the second shaft.
A cast-in-place or concrete block staircase by comparison can take weeks to build, he says.
What a CLT building will require more of, however, is fasteners. The 62,000-square-foot hotel required 201,000 fasteners, ranging from three-inch nails to "really long screws" tying a five-inch wall to a seven-inch floor slab to meet the military’s blast-resistant requirements, he says.
Morrow sees "the sweetspot," where CLT is most economical in the U.S., in buildings six to 10-storeys high. U.S. building code authorities are reluctant to permit wood construction above 10 storeys, he says.
But it will take some trailblazing to convince subcontractors that CLT goes up faster and cheaper than conventional construction, he says, noting that at the end of the project the elevator core and exterior brick contractors were impressed by "how true" the walls were.
The Alabama hotel required 63 truckloads of CLT material. It was supplied by Nordic Structures of Quebec.
Canada is paving the way with builders completing CLT buildings of six storeys and taller in several provinces, Morrow adds.
Canada’s largest is Brock Commons, a 17-storey building recently completed on UBC’s Vancouver campus. It is comprised of CLT and glulam and a concrete elevator core, says Steven Street, technical manager, Ontario Wood WORKS!, which hosted the Wood Solutions Fair at the Allstream Centre in Toronto.
Street says while Canadian builders are ahead of their American counterparts, he expects that CLT will catch on quickly in the U.S.
He sees the move to pre-engineered wood as a link "with our past connections with heavy timber."
Laminated timber buildings were erected in the late 19th and early 20th centuries. Many of those large wood members were actually small-dimensional lumber that were nailed together to increase strength.
Street says in some instances nail-laminated timber (NLT) is an economical option to CLT and he suggests NLT might be easily produced by roof truss manufacturers.
Street sees the movement to pre-engineered wood constructed buildings growing quickly in the next few years as more developers see its benefits.
"You may be able to double or triple the amount of work you do with the same team (of carpenters/labourers). It should be easier (work) as well," says Street, noting that using cranes, zoom-booms and other machines to do much of the heavy work will help to extend the working lives of crews.