Seven Benefits of Panelized Mass Timber
By Reed Newcomer, PE – Mass timber has become increasingly popular in the building industry in recent years and has placed exposed wood construction into the limelight. Given its many benefits, it is understandable why mass timber has gained popularity. Aside from being aesthetically pleasing, research has shown that mass timber buildings can provide occupants with both physical and psychological benefits. The characteristic properties of wood and proportioning of mass timber panels also provide numerous advantages to building owners that are deeper than just architectural appeal. While there are many other reasons to consider mass timber for your next building project, we have seen that our clients have selected a panelized mass timber system because these seven benefits have aligned with their building objectives.
1. Ease and Speed of Construction and Prefabrication
Mass timber panels are manufactured for specific projects and prefabricated in a controlled environment. Panels are cut to size with high-precision and small tolerances that include openings for doors, windows, stairs, chases, and ducts. Many manufacturers ship panels with pre-installed lifting straps and provide truckload sequencing so the panels arrive onsite for just-in-time scheduling. This also makes them ideal for projects with limited on-site storage capacity.
In turn, prefabrication reduces the need for onsite skilled labor as the installation can be performed by fewer non-specialized workers. More of the labor needed on mass timber projects is completed in a factory rather than on-site when compared to traditional steel or concrete structures. Since mass timber building shells can be constructed significantly faster than traditional buildings, other trades can start work sooner. In addition, mass timber buildings typically have fewer interior finishes to show off the wood structure.
Typically, all the penetrations are completed in the shop, which requires the mechanical, electrical, and plumbing trades to be coordinated in the design phase. When field modifications are needed, changes on mass timber projects can be made onsite with simple hand tools (drill, replicating saw, chain saw, etc.) and non-specialized labor due to the nature of working with wood vs. steel or concrete. The benefits of prefabrication allow the trades to complete their work on an accelerated schedule and the tenant to move in sooner.
2. Cost Efficiency
Light-frame construction is still usually the most economical system for most low-rise applications. Mass timber buildings, when designed effectively, have similar material costs to concrete and steel alternatives and are particularly more cost effective on large, regularly shaped structures and in situations where fabrication is repetitive. Mass timber sets itself apart from its concrete and steel counterparts since the framing components are about 20– 30 percent lighter, which translates to smaller and less expensive foundations, columns, and lateral systems for earthquakes.
Mass timber’s main cost advantage is the faster construction time. A quicker construction schedule means fewer carrying costs and time for interest to accumulate. Cost decreases also come from reducing on-site labor, skilled labor, and coordination errors. Fewer onsite workers coupled with shorter construction schedules also reduce the risk of job site safety incidents.
3. Structural Strength and Stability
Mass timber panels are primarily used as vertical load-carrying plate elements in structural systems such as floors, roofs, and walls. Mass timber is constructed out of slender wood elements that are prone to buckling when used alone. By connecting all the slender wood elements together to form a panel, they greatly increase the stability and redundancy of each wood element. Where dowel-laminated timber (DLT) and nail-laminated timber (NLT) can only effectively span in one direction, cross-laminated timber (CLT) can span in two directions without additional components.
Due to their orthogonal layers, CLT panels have been shown in laboratory tests to create effective lateral load-resisting systems. The panels performed very well in seismic testing with almost no damage and no residual deformation. Though their acceptance as a lateral force resisting system in the building code is not yet prescribed, it is still advantageous to use CLT shear walls due to their seismic resilience.
4. Thermal and Energy Performance
The two main types of energy loss in buildings are air transfer and thermal conductivity. The panel sizes and precise tolerances attributed by the mass timber manufacturing process result in fewer and tighter joints that promote less potential for airflow and a tighter building envelope. Mass timber panels also act as part of the insulative system of the building with thermal conductivity (R value) of approximately 1.2 per inch of thickness. Not only does the mass timber panel replace some of the insulation, but because it is solid wood it also acts as a thermal mass to help preserve the internal temperature of the building.
5. Fire Performance
Mass timber performs exceptionally well during fires due to the inherent nature of thick timber members that slowly char at a predictable rate due to their self-insulating properties. Mass timber panels can maintain significant structural capacity for an extended duration of time when exposed to fire.
Fire protection can be achieved by either encapsulating the mass or by allowing a sacrificial portion of the CLT to char. The encapsulation method would typically entail covering up the panels with layers of ‘Type X’ gypsum board. The char method allows the CLT to be directly exposed to fire by tolerating an approximate sacrificial depth of charring in the structural design. The char layer formed during combustion acts as an insulating layer so the interior can maintain its strength.
6. Environmental Sustainability
Wood grows naturally and when manufactured from sustainably managed forests, is a renewable resource. Stringent sustainable management practices in the U.S. and Canada prevent forest depletion while maintaining biodiversity and wildlife habitat. Life-cycle assessment studies have shown that wood outperforms steel and concrete in terms of embodied energy and air pollution. Wood also has a lighter carbon footprint because wood products store carbon absorbed by the trees while growing, and wood manufacturing requires less energy and results in less greenhouse gas emissions (go here for more information). Depending on the manufacturer and the forest where the wood originated, mass timber can also be used for LEED certification or other green building rating systems.
Even though mass timber construction uses large quantities of wood, it contributes to the efficient use of the resource. Since Mass Timber uses small dimensional materials that might not otherwise be used in structural applications, it allows manufacturers to utilize more of the tree. Finally, since mass timber panels are manufactured specifically for each project, there is almost no job site waste.
Perhaps one of the most significant attractions to mass timber is the aesthetically pleasing nature of wood. Research shows that exposed wood in an indoor environment provides occupants with physical and psychological benefits. In the western United States, many of us spend a significant amount of time outdoors which is one of the main reasons we live here. Using mass timber is one way to bring the outdoors into interior spaces, something that resonates with a significant part of the population.
Mass timber is a revolutionary building material for the construction industry with many economic and environmental benefits. Though there are a lot of good applications and benefits of panelized mass timber, it is not the solution for every building. If you are considering using CLT, DLT, or NLT in your next building, it is important to have early, pre-design discussions with your engineering team to determine if it meets your project goals and constraints. We are happy to answer questions and discuss issues and solutions specific to your next project.
Reed Newcomer, PE is a structural engineer based in Morrison-Maierle’s Bend office. He can be reached at email@example.com
Technical review of this article provided by Maria Chesnut, PE, MLSE.