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Mass Timber and Water: Understanding the Risks

Over the last few years, Mass Timber construction, specifically the use of cross-laminated timber (CLT), has gained significant attention in recent years as a sustainable and cost-effective alternative to traditional building materials like concrete and steel. While using a new material can be ground breaking, as with any construction material, its important to understand the potential risks associated with mass timber, particularly when it comes into contact with water for extended periods of time.

Water is a critical factor in the life cycle of wood, as it can both facilitate and impede wood’s growth and decay processes. When wood is exposed to water for long periods of time, it can absorb moisture and become saturated, leading to potential issues such as dimensional instability, rot, and mold growth. In mass timber construction, where CLT panels are used to create building components such as walls, floors, and roofs, its critical to ensure that the panels are protected from moisture throughout the construction process and beyond.

One of the main risks associated with mass timber construction remaining wet for long periods of time is dimensional instability. When wood is exposed to water, it can swell and expand, leading to potential issues such as warping and splitting. This can affect the structural integrity of the building and potentially compromise its safety. Additionally, if the wood is not allowed to dry properly, it may shrink and contract over time, leading to potential issues such as cracking and buckling.


Another risk associated with mass timber construction remaining wet for long periods of time is the potential for rot and decay. When wood is exposed to water and other environmental factors, it can become a breeding ground for fungi and other microorganisms that break down the wood fibers, leading to potential issues. This can compromise the strength and durability of the building, potentially leading to costly repairs and even structural failure.




Mold growth is another potential issue associated with mass timber construction remaining wet for long periods of time. Mold thrives in damp, humid environments, and can lead to potential health issues such as respiratory problems and allergies. Mold growth can also compromise the structural integrity of the building by breaking down the wood fibers and weakening the building components.


If we were to illustrate mass timber and what happens when it gets wet, we'll use the example of wet clothes in a pile.

Both materials can suffer from mold growth when exposed to water for extended periods of time. Wet clothes left in a pile on the floor can take a long time to dry out, as the moisture is trapped between the layers of fabric, and there is little airflow to facilitate drying. This is similar to wet CLT, which can also trap moisture within the layers of the panel and prevent proper drying.

On the other hand, spreading out the wet pile of clothes into open air can facilitate drying by increasing the surface area of the fabric and allowing for greater airflow. This is more akin to traditional stick frame lumber construction methods, which typically allow for greater ventilation and airflow than mass timber construction. This increased ventilation can help prevent moisture from becoming trapped within the building components and facilitate proper drying if moisture does become present.


To mitigate the risks associated with mass timber construction remaining wet for long periods of time, its important to follow proper construction and maintenance practices. During the construction process, its crucial to protect the CLT panels from moisture and ensure that they are properly sealed and ventilated. This may involve using waterproof membranes, installing drainage systems, and using proper flashing and sealing techniques to prevent water infiltration.

After the building is completed, it's highly important to regularly inspect the building components for signs of moisture damage, such as warping, cracking, and discoloration. Any signs of damage should be addressed immediately to prevent further damage and potential structural issues.


Although mass timber construction has numerous advantages, it's crucial to comprehend the possible hazards that could arise from prolonged exposure to water. To guarantee the building's long-term durability and safety, appropriate construction and maintenance practices can be implemented to mitigate these risks. It's advisable to collaborate with experienced professionals who possess the expertise to manage these risks effectively, ensuring a successful project outcome, as is the case with any construction project.


If you would like to learn more about moisture in mass timber, we host a lunch and learn session surrounding this topic. Contact us here, to book yours today!


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