Sustainability Spotlight: Mass Timber

What is Mass Timber?

‍

Mass timber is made up of several solid wood panels that are nailed or glued together, creating a component that has greater strength than the individual panels alone. There are several types of mass timber construction:

‍

• Cross-laminated Timber (CLT): Similar to plywood, CLT is constructed by layering panels on top of each other at 90-degree angles. Unlike plywood, which uses veneers, CLT uses solid wood making it much more durable than plywood. For the best visual representation of CLT, think of how you would stack the wood pieces when playing the game Jenga, but instead of laying them unaffixed, each piece would be glued or nailed, creating a solid structure.

• Nail-laminated Timber (NLT): This method uses nails to mechanically fix dimensional lumber pieces to each other and create a stack. Unlike CLT which requires a manufacturing facility to create, NLT can be created on the jobsite, making it a versatile option.

• Dowel-laminated Timber (DLT): An all-wood construction of mass timber, DLT foregoes the nails used in NLT and replaces them with wooden dowels.

• Glue-laminated Timber (GLT): A great choice for visible columns and beams, GLT removes the mechanical fasteners and uses glue for the bond, offering enhanced visual aesthetics and a streamlined look.

How is Mass Timber Changing the Game?

‍

Wood has many benefits in construction, such as its relatively low cost, light weight, and high availability. But the main drawback to wood is that it isn’t strong enough to support large, high-rise structures. Therefore, it makes sense that residential homes and small business structures are primarily made of wood framing, while modern high-rise structures are almost exclusively made of concrete and steel.

‍

Mass timber may be changing the game. Due to its incredible strength, the possibility of building large high-rise structures out of wood is being revitalized. Some mass timber can be as strong as steel and is 5 times lighter than concrete. This exceptional strength-to-weight ratio makes for a compelling argument when considering material choice for large structures.

‍

In addition to its strength and weight benefits, mass timber checks the box for several sustainability factors that concrete and steel do not. It is readily available and can be procured using sustainable forest harvesting practices. It produces far fewer carbon emissions than steel and concrete and acts as a carbon sponge, storing carbon rather than emitting it. Lastly, it is highly recyclable and can be salvaged during demolition and re-used much more efficiently than steel or concrete.

Drawbacks to Mass Timber

‍

Despite the environmental and construction benefits to mass timber, there are some drawbacks to it that architects and contractors should take into consideration. It is prone to water damage and requires more effort to treat and maintain than concrete or steel. And while wood itself is more cost effective than concrete and steel, mass timber can be more expensive upfront than its counterparts. That said, when evaluating the cost of a construction project, there are many factors that influence the bottom line, and mass timber can make up for its higher raw costs by way of faster timelines to completion as it is much more efficient to manage on the site than concrete and steel.

‍

Another potential drawback to mass timber is the lack of support from insurance companies. As technology advances and a track record is proven, this may become less of a concern. But it is worth noting that you may be looking at higher premiums to insure a mass timber-built structure than a traditional steel or concrete building.

‍

Not surprisingly, insurance companies justify their concerns with mass timber around the topic of fire resistance. There is debate over whether mass timber outperforms steel and concrete in a fire. When properly treated and protected with non-combustible materials, there is certainly an argument that mass timber is the better choice due to timber’s innate ability to char first, protecting the core from the flame. However, it is still wood, and that may be enough for insurance companies to be hesitant to give their blessing.

‍

That said, there are also positive to mass timber as it relates to fire resistance. It would lose its strength at a lower rate than steel and it does not conduct heat as well as concrete, potentially slowing the spread of the fire.

Examples of Mass Timber in High-Rise Buildings

‍

Mass timber in high-rise buildings is not an unknown commodity. There are several examples of its use in modern high-rise structures:

‍

• Ascent Building, Milwaukee, WI: Constructed in 2022, the Ascent Building is a 25-story skyscraper and is the world’s tallest building made from mass timber

• Haut Residential Building, Netherlands: This structure uses CLT for its load-bearing inner walls and stands 21 stories tall

• Sara Kulturhus Centre, Sweden: Using a combination of CLT and GLT, this structure was designed to be carbon negative over its lifetime

• Brock Commons Tallwood House, Canada: Formely the tallest mass timber building at the time of completion in 2017, this structure was built with a combination of concrete cores, CLT floors, and GLT columns.

Conclusion

‍

Mass timber is one of many innovative materials that allow businesses to take steps toward achieving their sustainability goals. As is the case with all innovations, there will be early adopters and late arrivals, and mass timber is no different. It continues to gain traction and has a strong portfolio of use cases to boast, making the future bright for this material.