What is Mass Timber Construction?
Mass timber construction, in contrast to light-frame wood construction, is built using a category of engineered wood products typically made of large, solid wood panels, columns or beams often manufactured off-site for load-bearing wall, floor, and roof construction. Mass timber is engineered for high strength ratings like concrete and steel but are significantly lighter in weight. Mass timber products are thick, compressed layers of wood, creating strong, structural load-bearing elements that can be constructed into panelized components. They are typically formed through lamination, fasteners, or adhesives. Mass timber can complement light-frame and hybrid options and is an environmentally friendly substitute for carbon intensive materials and building systems.
What Is Tall Wood Construction?
As technology advances, the definition of what constitutes a tall wood building is evolving and rising in height. Taller wood construction can span all-wood mass timber and light-frame systems beyond six storeys to mass timber-concrete-steel hybrid systems more than 18-storeys and rising.
As a safe, viable alternative to steel and concrete, mass timber construction is increasingly being used in taller buildings beyond six-storys. Canada’s national building code permits 12 stories of mass timber construction, taking into account its strength and fire resistance ratings. This change reflects a rigorous review by the National Building Code committees, as well as experts such as fire safety specialists, structural engineers, architects, scientists and builders.
Some provinces, such as British Columbia, Ontario and Quebec have already permitted mass timber structures of up to 12 stories in advance of these code changes. In BC, an increasing number of communities qualify as early adopters having met provincial requirements including support from their city council, planning and fire departments along with land use bylaws permitting tall wood construction. And the City of Vancouver has amended its building bylaws to allow mass timber construction up to 12 storeys for residential and commercial use. In BC, there are currently seven projects in the design phase and five under construction that are over 12 storys.
Components And Systems Of Mass Timber And Taller Wood Construction
Mass timber products are the building blocks that make taller wood construction possible. Products in the mass timber family include cross-laminated timber (CLT), dowel-laminated timber (DLT), glue-laminated timber (glulam), laminated strand lumber (LSL), laminated veneer lumber (LVL), parallel strand lumber (PSL), and nail-laminated timber (NLT ). Mass timber and engineered wood products can be used in an array of applications and is the foundation of taller wood building systems.
Types Of Mass Timber Framing Systems
There is an ever-evolving number of options and systems when it comes to mass timber. Using various combinations and sizes, mass timber products can serve as beams, columns, floors, roofs, and walls considering the directional strength of each wood products.
In contrast to conventional concrete and steel systems that tend to follow standard templates, mass timber systems offer the potential for greater flexibility, albeit not without some challenges. Types of mass timber framing systems include:
Post-and-beam mass timber systems are a popular choice, and resemble the common approach used in historic heavy timber buildings of the past. It is a skeletal framework of decking, beams and posts supported on a foundation. The upright wood members are referred to as posts and the horizontal wood members referred to as beams. The post and beams are connected using mechanical steel fasteners. This system of construction requires no load-bearing walls. Glulam frequently serves as posts and beams. Decking systems can be made of panelized mass timber products such as NLT, CLT or others. The post-and-beam system works well for open plan designs such as offices and commercial buildings.
Mass Timber Floor And Wall Systems
In contrast to post-and-beam, designers can take advantage of mass timber panel’s two-way spanning capability. This can include mass timber panels constructed to form a honeycomb structure well-suited to handle both vertical and lateral loads. In these systems, mass timber panels—similar to reinforced concrete and steel—form both floor and wall, with the walls bearing the load of the structure. In some instances, mass timber may form the core of a building, in place of concrete.
Hybrid Mass Timber Systems
Hybrid mass timber systems is a broad category that refers to any combination of wood, steel, concrete and other possible materials and building systems. Capitalizing on the performance and strengths of each building material, hybrid systems offer lots of flexibility. This can include a nearly all-wood solution that combines light-frame wood construction with mass timber panels, where only the foundation is concrete, and the connectors are metal.
For Further Reading:
• Think Wood has recently posted an article discussing mass timber at: https://www.thinkwood.com/mass-timber
• ” Mass Timber: Knowing Your Options” is an article featured at Structure Magazine: https://www.structuremag.org/?p=10916