CLT vs Glulam: Mass Timber Guide
Sep 14
3 min read
All across Canada, forests are now helping to form the main structure of buildings, not just supplying framing lumber. This method is known as mass timber. Two main engineered wood products are at the centre of this approach. People often mention them together, but they actually work quite differently when it comes to supporting a roof.
Many people use the terms cross-laminated timber (CLT) and glue-laminated timber (glulam) as if they are the same, but they are not. Knowing how each one is made, and especially what each is used for, is important for making a mass timber project successful, not just attractive.
Both materials begin the same way. Pieces of lumber are glued together with a strong, moisture-resistant adhesive, creating something stronger and more dependable than a single piece of wood. After this step, though, they become quite different.
CLT is made by stacking layers of lumber. Each layer is set at a right angle to the one below it, usually in odd numbers such as three, five, seven, or sometimes nine. This is why it can be used in two directions at the same time, similar to a concrete slab, making it perfect for flat parts of a building, like walls, floors, and roofs.
Glulam is made differently. Each layer runs in the same direction, with the grain aligned end-to-end, concentrating its strength along a single line. This makes glulam ideal for columns, beams, or trusses that need to carry weight in a straight, predictable way. Glulam has also been used much longer than CLT. European builders were laminating beams in the 1800s, long before Austrian and German researchers developed the modern CLT panel system in the 1990s. After these materials leave the factory, CLT acts like a prefabricated slab. It arrives with door and window openings already cut, goes up quickly, and provides real fire resistance, sound dampening, and insulation. Its main weakness is water. If left exposed to the weather, CLT can be damaged by moisture, so it almost always needs protection near a building's exterior, such as a rainscreen, soffit, or a large overhang.
Glulam is great for long spans and open spaces. Since its strength is focused in one direction, it works well as columns, beams, and trusses that span large areas without extra support, such as exposed roof structures, portal frames, or open lobbies. Glulam is also better for outdoor use. When properly treated and detailed, it is often used for exterior canopies, railings, and balustrades. It is also very efficient for its weight. Glulam can be stiffer than steel yet weigh much less, reducing foundation loads and making it easier to move large pieces onto a busy city site.
Neither material is meant to take the place of the other. On most large mass timber projects, both are used together, each doing what it does best. Glulam supports the structure, while CLT covers it.
Canada did more than adopt mass timber. The country helped show that it could work on a large scale, and building codes are still catching up to what engineers have already achieved. The 2020 National Building Code recognized encapsulated mass timber construction as a building type and set a height limit of 12 storeys. In 2024, British Columbia allowed these buildings up to 18 storeys, and Ontario will do the same in January 2025. The 2025 national code has since raised the height limit to 50 metres, and further changes are being considered.
The building that began this conversation still stands on UBC's Point Grey campus in Vancouver. Completed in 2017, Brock Commons Tallwood House is 18 storeys and 53 metres tall. It uses Douglas-fir glulam columns that directly support five-ply CLT floor panels. No beams are needed because of CLT's two-way spanning strength. At the time, it was the tallest mass timber hybrid building in the world, built almost entirely from timber made in British Columbia.
Nearly ten years later, on Toronto's waterfront, Limberlost Place at George Brown College is telling a similar but unique story. Its ten storeys are supported by black spruce glulam columns, which are among the largest in North America, along with a beamless system of CLT-and-concrete composite floor "slab bands." The building is designed to achieve net-zero carbon emissions and is already influencing updates to national and provincial codes for mass timber buildings taller than six storeys. This idea from the West Coast is now taking root in Eastern Canadian spruce.
