The Mass Adoption of Mass Timber: Benefits and Barriers
By Kate Zeile
Mass timber has been attracting a lot of buzz in recent years for its up-and-coming role as a sustainable, renewable alternative to steel and concrete building materials. Oftentimes, the most sustainable and healthy solution is the one that is most in-tune with nature. Mass timber buildings exemplify biophilic design and bring beauty and nature indoors, which has been proven to drastically improve human health, well-being, and productivity. Majestic, towering trees serve as the backbone and structure of our natural environment – why not for our cities as well?
What is mass timber?
Graphic courtesy of Forestry Innovation Investment. Click to enlarge.
Mass timber is formed by securing smaller pieces of wood products together into layers using glue, dowels, or nails. This process creates solid wood panels, beams, and columns that are structurally sound, remarkably strong, and flexible. There are several types of mass timber, which vary based on how the wood is layered and secured together.
- Cross-laminated timber (CLT): CLT is one of the more commonly used forms of mass timber in buildings. Layers of lumber are glued together at 90-degree angles to form structural panels. CLT is used for load-bearing walls, rooves, and floors and is especially suited for tall mass timber buildings.
- Glue-laminated timber (Glulam): Glulam consists of parallel layers of lumber that are glued together with structural adhesives. A variety of products can be formed from glulam, including beams, columns, panels, and arches.
- Dowel-laminated timber (DLT): DLT is formed by layering lumber either parallel or at 90-degree angles and securing the layers together with wooden dowels. DLT is the only mass timber product made entirely of wood, without the use of adhesives or fasteners. DLT therefore supports a Circular Economy and is a great Design for Deconstruction method. Design for Deconstruction reduces the risk of the material being sent to the landfill at the end of its usable life.
- Nail-laminated timber (NLT): NLT creates large structural panels by securing parallel layers of lumber with nails or screws. It is mostly used for floors, walls, and ceilings. This is another great Design for Deconstruction method –“screws not glue.”
- Laminated veneer lumber (LVL): LVL consists of parallel layers of wood veneer glued together to form panels that can be used for beams or rafters.
- Mass plywood panel (MPP): MPP is one of the newer mass timber products. It is created by gluing together thin, dense veneers to form large panels that can be used as platforms, beams, and columns.
- Laminated strand lumber (LSL): LSL is made by pressing together short, thin strands or flakes of shredded wood and bonding it using an adhesive. The final product is large blocks that can be used for structural framing.
- Parallel strand lumber (PSL): PSL is created by bonding together long, parallel strands of veneer using an adhesive. It is very strong and flexible, making it suitable for use as beams and columns.
Mass timber boasts benefits for nearly all aspects of the building process, yielding positive results in design aesthetic, construction time and costs, and sustainability.
One benefit of mass timber is its biophilic aesthetic and strong impact on health and wellness. Exposed wood on the interior and exterior of mass timber buildings allows for uniqueness and differentiation compared to conventional metal and concrete structures. Using the natural material of wood also incorporates biophilia into mass timber buildings, which is extremely impactful on human health, well-being, and productivity.
Mass timber buildings are shown to save costs and time in the construction process. According to a comprehensive Mass Timber White Paper by the Central City Association of Los Angeles, compared to conventional tall steel and concrete buildings, mass timber buildings are significantly lightweight. This allows for smaller foundations, which results in savings in both construction cost and schedule. Mass timber buildings result in shorter construction schedules for several other reasons as well: Mass timber products are prepared off-site, reducing the need for material preparation and staging, therefore saving time and labor costs. Eliminating the use of concrete in building roof and floor assemblies significantly shortens the construction time of mass timber buildings, since the concrete curing time is eliminated. In exposed mass timber buildings, there are also noteworthy cost savings from reduced construction assemblies (gypsum board, paint, etc.) in the exposed portions. Though material costs vary widely depending on location and timing, locally sourced timber products are not subject to tariffs, which also results in cost savings.
Another huge selling point is that mass timber buildings are sustainable and renewable alternatives to conventional steel and concrete buildings. Unlike concrete and steel, mass timber is renewable when harvested responsibly and sustainably. With responsible forest management, wood as a building material will never be depleted. Additionally, wood captures and stores carbon dioxide from the atmosphere during photosynthesis, making mass timber a carbon sequestering material. Mass timber buildings similarly have low embodied carbon as compared to conventional buildings since the manufacturing and construction process is much less energy-intensive. The overall life cycle impacts of mass timber buildings are significantly reduced when compared to conventional steel and concrete alternatives, making it the more sustainable choice. Additionally, as we all know, the supply chain is extremely volatile right now, so the lead times for obtaining conventional steel and concrete materials can be much longer than for mass timber. Using locally sourced timber offers even greater benefits as a result of its reduced transportation impact, lower carbon footprint, and positive support of local economies.
Though mass timber is a very promising building strategy, there are some barriers to its mass adoption. Since tall mass timber buildings are still an emerging phenomenon, there is a lack of expertise in the workforce, which could be mitigated by further education and training. Mass timber products are manufactured through a specialized process, and as of now there is a shortage of manufacturing capacity limiting its widespread adoption. And as previously noted, in order for mass timber buildings to be sustainable and renewable on a large scale, timber must be harvested from responsibly managed forests to avoid mass deforestation.
Obtaining loans and insurance for mass timber buildings poses a challenge for project teams as well. Since mass timber products are prepared off-site, some construction costs are front-loaded as compared to conventional steel and concrete buildings, which has empirically made it more challenging to obtain loans. Additionally, insurance companies may be hesitant to insure mass timber buildings since the technique is emerging and unfamiliar. There are still some hurdles to overcome when it comes to code approval as well, especially for very tall mass timber buildings. Although the International Code Council approved the construction of mass timber buildings up to 18 stories tall in 2018, local code officials may still be tentative to approve mass timber projects due to unfamiliarity. However, as of July 2021, the State of California implemented supplementary code provisions intended to streamline the process of approving and executing tall mass timber buildings. Perkins&Will breaks down the code changes nicely in their article, California Catches up on Mass Timber.
One final intricacy of mass timber buildings is its relation to fire safety and protection. Mass timber products are fire resistant as a result of the wood charring process, which protects the interior and enables it to remain structurally sound. However, to demonstrate compliance with fire-related sections of the building code, mass timber construction must meet various size and testing requirements based on the type of construction, and the type of construction dictates when and where mass timber components can be used. Coupled with the fact that the fire performance of mass timber buildings is still being studied, this can be quite a complex topic! WoodWorks’ Fire Design of Mass Timber Members provides a great overview of fire design considerations of mass timber buildings.
Mass timber construction offers a sustainable, beautiful, biophilic, and efficient alternative to conventional steel and concrete construction. With any up-and-coming building technique, there are inherently obstacles to overcome. However, with further research, education, advocacy, and successful case studies forging the way, the mass adoption of mass timber is possible.
Interested in learning how your building design can lower its carbon footprint and perform more sustainably using mass timber? Contact firstname.lastname@example.org to learn about our life cycle assessments (LCAs).
- Mass Timber Resources from WoodWorks
- Mass Timber Resources from naturally:wood