Overcoming Moisture Issues in Mass Timber Projects

Mass timber is changing the construction industry, offering a sustainable, efficient, and aesthetically pleasing alternative to traditional building materials. However, these benefits come with unique challenges, as the moisture induced effects and thermal properties of mass timber differ from those of steel and concrete. To ensure the success of any mass timber project, it is important to monitor and analyze the moisture content of the wood from start to finish. From the moment the timber leaves the factory, through transportation, storage, and on-site construction, contractors need to pay close attention to detail.

1. Transport and Storage

Mass timber is considered “dry” at a typical moisture content range of 12-19% when leaving fabrication. However, materials can pick up moisture during transit, storage or during installation from ambient conditions or from exposure to elements or other moisture-latent construction materials. Shipping protection, travel distance from the manufacturing facility, transit time and site storage can all impact the mass timber’s exposure.

• Transportation: Transporting mass timber panels requires careful planning to avoid any damage and keep the moisture content low to reduce shrinking or swelling of the wood.
• Storage: Once on-site, panels must be stored in a dry area under protective wrapping with adequate drainage. If material is not ready for installation, it should be positioned on appropriate dunnage support, 8” off the ground.
• Sensor Application: To offer additional protection and monitoring, incorporating sensors during storage can provide real-time data on environmental conditions and wood moisture content. These sensors can alert project managers to any issues such as temperature fluctuations or unexpected moisture, ensuring the timber remains in optimal condition until it’s ready for use.

2. Construction

One of the most critical aspects of mass timber construction is managing moisture. Humidity control through effective temporary climate equipment and technology can help mitigate moisture issues onsite and support building acclimation.

• Using Effective Equipment: In most climates, heat and particularly direct-fired heat is the least efficient way to manage moisture in mass timber, yet it is often chosen due to its significantly lower cost. Desiccant dehumidification is the most efficient way to manage moisture for mass timber and other construction materials. It is especially efficient when paired with supplemental heating or cooling. While temperature (heat) is a relative and indirect method of managing moisture, desiccant dehumidification offers a precise and direct approach removing the moisture content in the air and surrounding materials.
• Monitoring Moisture Levels: Continuously monitoring moisture content is essential to maintaining target moisture levels. Wood with a moisture content above 26-30% can support fungal decay, so having real-time data provides contractors with visibility and control over interior environmental conditions and wood moisture levels. This approach not only protects materials but also helps keep projects on schedule. Data can also be used to automatically control climate equipment ON/OFF. Therefore, teams do not need to manage equipment on site reducing labor, energy cost, and human error.

3. Structural Capabilities and Limitations

When mass timber assemblies are exposed to long-term moisture or standing water, it can penetrate deep into the wood, becoming trapped within the pore structure. Poor conditions or mishandling of the materials could impact the structural capabilities of the material and, therefore, the integrity and durability of the building.

• Structural Integrity: While mass timber is known for its strength and versatility, its structural performance can be significantly affected by moisture. Prolonged exposure to moisture, whether in liquid or vapor form, can lead to surface moisture content exceeding 20%, which is likely to foster mold growth. Without proper drying, mass timber can retain large amounts of water for extended periods, increasing the risk of mold and potential loss of structural integrity. Proper moisture control is not just about protecting the timber from environmental conditions but also preserving its structural capabilities.

• Load-Bearing Capacity: The load-bearing capacity of mass timber can be reduced if the moisture content exceeds safe levels. As the wood absorbs moisture, it can become more pliable and less capable of supporting the intended loads. Therefore, monitoring moisture levels is crucial to maintain optimal conditions and ensure the timber performs as designed throughout the building's lifespan.
• Connection Methods: Exposing wood to moisture can increase the risk for corrosion of metal fasteners or connections. Moisture can cause the wood around connectors to expand or contract, leading to loosening or misalignment. Using moisture-resistant sealants or incorporating designs that allow for movement without compromising structural integrity can enhance the durability of these connections.

Conclusion

Integrating mass timber into construction projects requires careful moisture management from the moment it leaves the factory until its installation. Proper transportation, storage, and construction practices, along with Polygon Climate Control’s technologies such as desiccant dehumidication and real-time monitoring, can help preserve the material’s integrity and avoid project delays. Contractors can maximize the benefits of mass timber while minimizing potential challenges, leading to innovative and resilient construction projects.

Contact us today to learn how our solutions can support your mass timber project.

Sources: 

• https://www.rdh.com/resource/mass-timber-building-enclosure-best-practice-design-guide-version-2/
• https://www.rdh.com/wp-content/uploads/2022/11/Mass-Timber-Moisture-Management-Guide.pdf