EDITOR’S NOTE
We are excited to welcome Connor MacKenzie and his new column Inside Mass Timber. Connor MacKenzie, is Vertical Market Manager – Solid Wood Systems & Mass Timber at HOMAG Canada. Drawing on hands-on industry experience and a front-line view of advanced manufacturing, the column explores trends, technologies, and real-world insights shaping the mass timber and solid wood construction sector across North America.
Around the corner from my house stands T3 Sterling Road. These sleek six and eight-storey office towers were completed in 2024 using Dowel Laminated Timber (DLT) and Glue Laminated Timber (GLT) components and represent the future of mass timber construction. Not long ago, structures of this size could only have been built with steel and concrete. Today, with the emergence of mass timber, that is no longer the case.
So, what is mass timber?
The phrase mass timber is an overarching term that refers to structural lumber that is either laminated or fastened together to create a larger, stronger, structural component. These components, typically columns, beams or panels, are used in structural building applications such as wall panels, floor systems and framing components in lieu of traditional steel and concrete construction.
While heavy timber framing has been used for centuries, access, availability and affordability of large, solid lumber cross sections has dwindled as the forestry industry has evolved. Additionally, when designing larger scale or span buildings, the load bearing and structural components require greater strength and tensile requirements that exceed what solid sawn timber can offer.
Enter mass timber! These laminated building components quite frankly change the game for architects, designers and builders alike. Not only are the mass timber components as strong as or stronger than traditional steel and concrete components, they are also lighter, easier and faster to build with, provide a drastically reduced carbon footprint when fabricating while concurrently utilizing natural and renewable resources and provide beautiful aesthetic properties.
In an economic and political landscape focused on sustainable practices, reducing our carbon footprint, addressing the ever-growing housing crisis, mass timber is situated to revolutionize the way that we build today, and create a better tomorrow.
Crossing your T’s:
All mass timber is constructed with structural lumber (traditionally softwood, namely spruce, pine or fir in North America). This lumber can be purchased machine stress rated (MSR) or graded using a series of scanning and grading technologies on site. Each type of mass timber has it’s own certification requirements outlining what structural rating the lumber needs to meet (depending on end use, application, building code, etc.).
With the basics outlined, let’s shift our focus onto the four key sub-sects of mass timber. Each type of mass timber is categorized by an acronym, with the core groups being GLT, CLT, DLT & NLT.
GLT (Glue Laminated Timber)
GLT (glue laminated timber – colloquially known as glulam) is the process of face-gluing boards together to create a larger cross-section laminate. Single lamellas (a single piece of lumber that is then laminated to create a larger component, traditionally nominal “2 by” lumber) can either be used at a common length direct from the mill (i.e. 10’-20’ lengths of solid sawn lumber) or finger-jointed together to create any desired length of “lam-stock.” The majority of GLT (and all mass timber) is built with finger-jointed lamellas, as finger-jointed lumber allows for better material yield, strength grading and enables the manufacturer to produce nearly any length of component they need, be it 14 feet or 40 feet.
GLT is predominantly used for vertical post and column or horizontal beam construction. Think vertical columns that support the peripheral structure of a building or load bearing cross beams that support floor or roof systems. While GLT components are traditionally straight, it can also be manufactured to be curved or cambered, allowing for both structural and architectural finishes.
CLT (Cross Laminated Timber)
CLT (cross laminated timber), similar to GLT, is a glue-laminated structural component. However, CLT utilizes both vertically and horizontally laminated lamellas, orientated perpendicularly to each other, creating a multi-layer structural panel. Traditionally constructed in three, five or seven layers, CLT is built using a sandwich of longitudinal and cross lamellas for multi-axis strength and structure. For example, a “3-ply” CLT panel uses long lamellas (creating the major/length axis) edge glued to one another, followed by a cross layer of shorter lamellas (creating the minor/width axis) in the middle, and a third layer (or ply) of long lamellas.
This building method utilizes cross-axis, multi-span strength and stability, provided by the right-angle oriented lamellas, allowing for use as structural panels, wall and floor systems. Depending on construction, these panels can traditionally span up to 12 feet in width by 60+ feet in length, which provides a pivotal structural component for multi-storey mass timber buildings. Concurrently, these CLT panels can be designed to be pre-built or pre-processed with window and door openings prior to shipment, eliminating on-site framing and expediting construction. In the growing eco-system of off-site & modular construction, CLT panels provide unbeatable erection times and drastically reduce on-site labour.
DLT (Dowel Laminated Timber)
DLT (dowel laminated timber) is our first non-glue laminated structural component. Similar to GLT, lamellas are laid-up face to face, but instead of glue, a long hardwood dowel is used to adhere and secure the lamellas to one another. This method of construction requires specialized machinery to drill and insert the long hardwood dowels, producing large span panels (also known as billets), similar to CLT panels. Friction fitting of the dowel not only secures the lamellas to each other, but also provides structural integrity to the panel.
Traditionally used as floor or ceiling systems, one of the key differentiators in DLT (and NLT) construction is that the lamellas used to make DLT panels are orientated on their edge. This allows for profiling of the lamella prior to construction, to provide channels or profiles on the face of the panel, which can be used to provide acoustic or insulative properties. This process makes DLT (and NLT) popular in applications such as concert halls and auditoriums, and often focuses heavily on aesthetic and external facing panels and components.
NLT (Nail Laminated Timber)
NLT (nail laminated timber) follows the same concept as DLT, utilizing fastening nails rather than glue to adhere lamellas. Similar to GLT and DLT, lamellas are orientated on their edge and are then nailed or fastened together to create a structural timber element. This system has been utilized for decades in stick frame construction, as boards can be nailed on site together to create headers, beams or columns. Traditionally popular in the agricultural buildings and warehouses for column construction, NLT has made a resurgence and gained popularity beyond standard post & beam construction, and has expanded as a panelized element.
As discussed with DLT, lamellas used in NLT panel construction can be pre-profiled prior to lay-up to allow for acoustic and insulative properties. This additional facet to the face of a panel has promoted the growth of the product far beyond its historical primary post & beam usage.
The future of mass timber
So, why mass timber?
Well, for starters, it’s a far greener construction method than traditional steel and concrete building materials. Mass timber construction can reduce embodied carbon by up to 40 per cent in commercial construction applications. Not to mention, lumber is a naturally occurring and replenishing resource, providing a more sustainable roadmap to material supply-chain as the growing market emerges.
Mass timber construction is also fast, and I mean really fast. The National Research Council of Canada estimates that mass timber construction can reduce commercial build times by upwards of 20 per cent. Recently, at the 230 Royal York project, a 9-storey, 60-unit residential building in Etobicoke, Ont., the construction team can erect nearly one story per day, with a greatly reduced labour force. Pair that with mass timber elements having the same, if not higher, fire-ratings and load ratings compared to traditional steel and concrete building elements, and the construction eco-system changes entirely.
With 696 completed mass timber projects in Canada and 81 currently under construction, ranging from institutional buildings, residential and commercial units, even bridges and recreational facilities, the tip of the mass timber iceberg in Canada is just poking through. n
References:
NRC Cost Comparison
The State of Mass Timber in Canada
Fact Sheet | Building Sustainably: Mass Timber (September 2023) | White Papers | EESI
Report: The state of prefabrication in Canada | Resources | naturally:wood
Technical: Mass Timber Through a Life Cycle Lens
