Cross-Laminated Timber (CLT) is an innovative and forward-thinking construction system that has made headlines in Portland recently. Originally developed in Central Europe in the mid-1990s as an alternative to stone, masonry and concrete construction, it uses manufactured wood panels (made up of smaller, and therefore more rapidly-renewable trees) to create buildings up to twelve stories high. Lately there are more and more buildings that display both the aesthetic potential of CLT, as well as its important economic and environmental advantages. Perhaps one of the greatest examples of this type of building is the Graphite Apartments in London, which inspired me to create these graphics.
Cross-laminated timber panels are formed by stacking and gluing together successive perpendicular layers of pre-dimensioned lumber. The layered stacks are then pressed in large hydraulic or vacuum presses to form an interlocked panel. The panel is then sized and shaped with a Computer Numerically Control (CNC) machine into a construction-ready component. The number of layers in a panel can range from three to seven or more, and panels can have door and window openings, plus routings for electrical and mechanical systems, before shipment to the building site.
The prefabricated panels with pre-cut openings for doors, windows, stairs, service channels and/or ducts are then shipped directly from the manufacturer to the job site where they can be quickly and efficiently lifted into place. (Some contractors even ship panels with preinstalled lifting straps.) The assembly is then done with the use of very few people and tools compared with other construction methods. The panels are often delivered “just-in-time” and erected right away, making CLT ideal for projects with limited on-site storage capacity.
One might first see these massive timber panels and wonder, “Why on earth would I need that big of a piece of wood to build with?” Well, there are several advantages besides the obvious ones related to easy manufacture and installation. One of the best resources on this topic is the 2013 CLT Handbook, which I referred to extensively in order to create this blog post and illustrations.
CLT panels are great fire resistant materials. Imagine trying to use 12-inch-diameter logs to start a camp fire… mass timber does not catch fire easily. In fact, CLT acts more like concrete. CLT can also be a “green” material, made from trees harvested from sustainably managed forests. It is cost competitive to other building materials but it has value added benefits: earlier project completion date thanks to quicker assembly, reduced foundation depth thanks to a lighter building structure, and increased job site safety due to the easier to handle materials and tools.
While it is still relatively new in North America, the benefits and beauty of CLT make it a really exciting construction system. We are excited to see the Framework Building go up in our own backyard. Let’s see how long it takes to see more of these beautiful buildings in our timber city.