A First: Working with CLT
Cross Laminated Timber (CLT) is a large-scale, engineered wood material that is stronger than steel and concrete and able to maintain its structural capabilities longer in a fire. CLT is manufactured by fusing together layers of thin wood (approximately 1.5 inches) with formaldehyde or polyurethane adhesives that comply with ANSI PRG 320. The prefabricated panels are then transported to the jobsite, hoisted into place, and secured utilizing a just-in-time (JIT) sequencing method. The JIT approach maximizes efficiency by minimizing the on-site tasks associated with the scope of work.
While Co|Lab is the first CLT building in Virginia, the product is quickly gaining momentum across the country. As AEC industry firms continue to research and test CLT, local and national building codes will continue to evolve to allow CLT to become a more mainstream structural material. The next iteration of the International Building Council (IBC) code will be implemented in 2021 and many industry groups are pressing for the admittance of tall mass timber—mass timber buildings that exceed current height limits for wood buildings set by the International Building Code.
“We carefully considered CLT’s sustainability aspects as a wood material when designing Co|Lab. The production process itself has little environmental impact, and because wood actually sequesters carbon over its lifetime, we saw CLT as an opportunity to help the industry push for reducing greenhouse gas emissions,” said Katie Rothenberg, HITT’s Vice President of Sustainability & Innovation.
The Co|Lab’s CLT is made from black spruce trees and sourced from Nordic out of Canada. Nordic was chosen for their Forest Stewardship Council (FSC) status and location; the Co|Lab materials must be within 1,000 km to meet the requirements for the ILFI Living Building Challenge Petal certification. Nordic partnered with the installation team from B&D Builders in Lancaster, Pennsylvania to erect the Co|Lab structure.
“Precision in every laser cut and steel piece is critical to ensuring a smooth installation.”
Our teams had many lessons learned from the experience of working with a completely new material and prefabrication approach:
Efficiencies are only as strong as the prefabricated work. Woodworks is an industry organization that offers case studies as a resource to the industry to share similar lessons learned. In their Jens Hackethal case study, beam sections were prepared in a facility with connections at the ready to further accelerate on-site operations. The Co|Lab project team found the extensive rigging and bracing was time-intensive at first, but after just a few panel installations, the fastening process quickened. Quickening the pace of individual job tasks can speed the process, but the CLT structure can present major implications to the project schedule. Leveraging prefabrication allows general contractors to shorten the construction schedule, typically enabling owners to generate cash flows on income-producing properties faster than traditional methods.
Have a (detailed) single source of truth. It is crucial the project has a highly detailed model that encapsulates all beams and connections. Precision in every laser cut and steel piece is critical to ensuring a smooth installation. Surveying accuracy is critical to ensure the columns are placed in the right location relative to the rest of the building and the foundation.
Site and building locations matter. The north side of Co|Lab lies on the lot line, reducing access during installation to only the east, west, and south sides. Unlike other structural methods such as concrete and steel, CLT only requires a lean installation team and a crane, but accessibility challenges can still impact the schedule. Detailed planning is required for sequencing the pieces as they need lay-down space on-site. This holds true for other types of sites, including urban downtown settings, mountainous regions, or sites located on inclines.
CLT presents an excellent opportunity for the building industry to utilize prefabrication as a solution to the skilled labor shortage. While there will always be a learning curve when working with new materials and approaches, leveraging partnerships through collaboration will ensure success.