Cross-Laminated Timber Comes To America

 OP INSTITUTIONAL ED PIC 1By Amanda Johnson

Cross-laminated timber (CLT) is a familiar construction method in Europe, but is just beginning to hit its stride in the United States, making its way into new buildings and combining a much sought-after sleek, clean and modern vibe with the authentic, warm character of wood. While it previously would have been unheard of for wood to replace steel and concrete as a structural element in larger buildings, CLT is changing everything. Here's what you need to know about it, why you should be using it, and on-the-ground tips for success.

What is CLT?

CLT is made from engineered wood panels laminated together in alternating directions to enhance its strength. The end result is an exceptionally stable and solid material with a look that redefines heavy, old-growth lumber.

Why Use it?

CLT is precision engineered and factory manufactured to exceptional levels of accuracy, often using computer numerical control (CNC) machines. This level of precision improves delivery speed, construction time and waste all valuable benefits that also have the potential to reduce costs. Those benefits aside, it is not often that new construction can expose its structure through such a warm, authentic material. In fact, many consider CLT the "modern brick and timber."

Columns, beams, and even entire floors and walls arrive on-site organized, numbered and precisely pre-cut – down to the millimeter which greatly reduces time spent in field verification and allows production and on-site labor to move along quickly. In addition, because the building structure generally weighs less than half the weight of steel or concrete, the foundation often costs less. The overall cost savings and advantages are obvious: not only are installation expenditures and material waste reduced, but an earlier completion date delights the client and means the space can be ready for use sometimes months ahead of a traditional construction schedule.

CLT also offers substantial waste reduction and environmental benefits. Because of its lower carbon footprint and the sustainable forestry practices used to harvest it, CLT is one of the greenest methods of construction available today. Trees are a 100 percent renewable resource and CLT is typically harvested from young, small-diameter trees such as spruce, Douglas fir and larch. This generates fewer greenhouse gas emissions than traditional construction types, and because CLT boards are pre-cut so precisely, there is far less landfill waste compared to other construction types.

Tips for Working with CLT:

Here are some suggestions to help ensure a smooth installation process, especially if the contractor or laborers are not familiar with CLT a common occurrence with a new product, but one that doesn't have to cause concern.

* CLT can be defined by building codes as a number of different types of construction. The primary is Type IV, which requires that no spaces are concealed. Although this leads to beautifully exposed wood columns and floors, be sure to review these requirements with all parties involved. Any tenant improvements (TI) work should be in compliance, with an understanding of how they intend to attach items to the CLT structure. Be prepared for other exposed items like mechanical ducts and shafts, electrical conduit, and sprinklers.

* Have early discussions with the local building department to review the project. Since CLT is a newer type of construction, many of these decisions, such as exterior exposed soffits, are interpreted differently by each jurisdiction. An early and open collaborative discussion with the building official will ensure a smoother construction process.

* Having a general contractor familiar with CLT definitely helps the process. The tight construction tolerances and quick erection time make scheduling especially important. Foundations and concrete shaft walls for CLT are much less precise, which can cause issues and slow down the CLT activities on-site. Panels are also shipped in exact order to unload and erect; any deviation from this leads to slower development on-site.

* Coordinating the project throughout design development with the CLT provider is an important step. A "design-build" contract in which 3-D models are shared between all disciplines is critical to anticipate conflicts in the field. Although not always feasible, having a GC for pre-construction services in an integrated design approach helps improve overall site time.

* Coordinating TI during the core and shell development is ideal. This allows for key critical items such as mechanical, plumbing and electrical penetrations to be coordinated and pre-routed during fabrication. An often-overlooked trade that generally comes in late in the process is the sprinkler subcontractor work. These penetrations can ideally be coordinated early, especially if the height of the space is critical for ownerships groups. If TI work follows much later, beams can still be pre-routed to anticipate tenant work. Having that integrated design approach helps facilitate great solutions to these types of issues.

Not only will using CLT immediately elevate a building's overall design and architecture with a rich, clean feeling that goes beyond the look of a standard new build, it also provides fresh, exciting and potentially more profitable construction opportunities.

Amanda Johnson is an associate principal at OZ Architecture, a top-tier design and architecture firm based in Denver with a 50-year-history of thought leadership, innovation and creative design solutions. Connect with Johnson at ajohnson@ozarch.com.  

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