Traditional building materials such as concrete and steel have been the leading components of large scale buildings for centuries. While they certainly have their cost, strength, and reliability advantages, a newer building material is becoming widely available and might just be the competition they need. Cross-laminated timber, or CLT, is composed of layers of wood and holds a competitive edge to standard building elements.
WHAT IS CROSS-LAMINATED TIMBER?
CLT is formed by adhering several layers of kiln-dried lumber together. Each layer is set perpendicular to each other and usually consists of three, five, or seven layers total. Once glued together, the panels are compressed and dried. This cross lamination provides stability and strength that traditional lumber cannot offer. In fact, CLT is comparable to the strength of concrete making it a practical material for use in tall buildings.
The use of CLT began in the early 1990’s throughout Europe and is a continuously widespread material choice across the region. It did not, however, catch on in North America until the 2010s and has slowly gained steady popularity due to a number of advantages. Once building project plans are finalized, cross-laminated timber can be fabricated in specifically dimensioned sections allowing minimal onsite modifications and reducing waste.
BENEFITS OF USING CLT:
When compared to competing building materials, such as steel and concrete, CLT offers labor and material cost advantages. CLT was found to be a more-cost effective option at between $5 and $20 per square foot compared to precast concrete panels at between $14 and $40 per square foot. Additionally, as CLT is typically a more lightweight material than concrete and steel alternatives, installation durations and labor quantities can be reduced.
CLT can be produced in large, prefabricated sections allowing it to be placed and secured immediately as it arrives onsite. Reducing the amount of onsite coordination and required measurements ultimately reduces the timeline of the project. Also, as soon as CLT is installed, it reaches its maximum strength and does not require lengthy curing or welding procedures.
The entire project team, including development and homeowners, feel peace of mind in using wood as a building element. Wood offers a reduced carbon impact as it can be renewed and repurposed at the final life of the building.
CLT offers a couple of safety measures that make for a better construction environment. Once assembled, CLT provides a strong working surface for additional trades to begin their installation processes. Additionally, as less fabrication needs to occur onsite, overall construction noise is reduced.
CLT doubles as an essential building material and a potential design element with its beautiful wood tones and grains. Architects have found a way to make CLT into a statement feature in residential and commercial applications.
While the popularity of CLT is certainly increasing, it might be harder to come by than traditional concrete and steel elements. Suppliers and fabricators must be properly trained and equipped to manufacture cross-laminated timber. Depending on the location of your project, this could result in lengthy production and shipping times.
As each panel of CLT is fabricated to specific measurements based on the project design documents, it can be tricky to make modifications after production. Onsite changes to the design of your building will require additional planning and re-fabrication of CLT sections. Be sure to inform the project structural consultants of any necessary changes.
If CLT is delivered to site and not able to be immediately installed, it can take up quite a bit of storage space. The large, prefabricated sections will need a designated location to be set aside and this real estate is not always available in congested environments.
A common reason architects and constructors are hesitant to build with wood is due to fire performance. Despite this concern, CLT is found to have substantial fire resistance. Due to the thick layers of timber in each panel, it will burn slowly at a predictable rate and maintain structural integrity for an extended period of time during a fire event.
WHAT DOES THE FUTURE LOOK LIKE FOR CLT?
As widespread use of mass timber products begins to increase, more authoritative agencies begin to offer their guidance. In 2015, the International Building Code (IBC) introduced the U.S. standard for Performance Rated Cross Laminated Timber. As building codes began to introduce CLT into their standards, it was originally limited to buildings less than six stories. Regulating agencies are taking a closer look into this and have introduced code changes to increase this number.
In 2018, the International Code Council (ICC) created three new types of construction (Types IV-A, IV-B and IV-C) which quantified fire safety requirements and number of stories for tall mass timber buildings. These new provisions are expected to be included in the 2021 International Building Code.
Governmental agencies are also playing a role in the advancement of CLT. In 2017, the Canadian government began a $39.8 million program aimed at supporting the use of wood in non-traditional construction projects, such as tall buildings. Mass timber may be a sustainable solution to the housing shortage that rampages North American countries. As wood is vastly available and sustainably produced, it presents a green alternative to this growing issue.
For consulting engineers in Vancouver contact Builtex Engineering Group. We are licensed structural engineers in BC available for structural engineering services. We specialize in structural design and site review of residential and light commercial construction projects including new homes and renovations.