Governments around the world are introducing policies that require architects and designers to consider using timber wherever possible in the construction of buildings. From France and Canada’s laws regarding the use of wood in new structures to Japan’s focus on timber in public buildings, there is a significant shift away from the use of concrete and steel calling for innovations in Mass Timber Construction (MTC) technologies.
Mass timber construction offers many benefits when it comes to sustainability and green environments:
- Timber is a renewable and sustainable resource.
- Wood stores carbon, which can reduce carbon dioxide in the atmosphere.
- Trees and timber products require less energy to produce than steel and concrete and help naturally remove greenhouse gases.
- Components constructed off-site reduce noise pollution, traffic congestion, and site waste with proper planning.
- Tall timber buildings can be completed up to 30% faster as smaller modules are precision cut and marked for rapid onsite installation.
- Timber construction can save onsite labor costs, as well as passing energy savings on to the property owner.
- Reclaimed and recycled timber used to create Cross-laminated Timber (CLT) gives further financial advantages.
- Mass timber plays well with other structural materials to create hybrid solutions.
- Unlike metal, timber has the ability to exchange moisture with the surrounding air to adapt to short-term changes in humidity and temperature.
International Building Code
The International Code Council (ICC) has released a package of 14 code change proposals for tall mass timber construction. Three categories of building types include allowable heights, areas, number of stories, and fire safety requirements. Guidelines based on several years of scientific research and testing will be described in the 2021 International Building Code (IBC) in late 2020:
- Type IV-A –Deals with gypsum wallboard on all mass timber elements at a maximum of 18 stories.
- Type IV-B –Describes the limits on allowed exposure of mass timber ceilings and walls at a maximum of 12 stories.
- Type IV-C –Explains the 2-hour fire resistance requirements for exposed mass timber at a maximum of 9 stories.
Tall Timber Factors
When building tall, it is necessary to account for flexibility, load paths, transfer, and uplift forces. It can be challenging to configure connections and hardware so that only incidental loads transfer via bolts. Load paths can cause materials to experience bending, compression, tension, torsion, or shear. Address this using wood grain panels parallel to the load path. Stairs and elevator shafts also transfer the load. Hybrid construction can provide solutions to a timber building’s uplift and lighter weight, as well as issues with acoustics in the floor, ceiling, and wall assemblies.
Dimension changes due to moisture content must be considered. The use of steel gusset plates can restrain changes causing splitting of the timbers. And, while mass timber buildings perform well in fire by developing a protective char layer as insulation, steel connections exposed to flames and heat can fail suddenly. Therefore, it is crucial to protect these hardware connections by using a fire-proof coating or embedding them inside the timbers.
Different structural advantages are found in balloon, hybrid systems, platform, post-and-beam, and massive timber bearing walls. Currently, residential buildings use smaller components with load-bearing walls, while commercial uses have open floor plans, using a more flexible system of weight-bearing posts connected by beams.
Modern mass timber structures are incredibly versatile for both large and small structures and can increase our efforts to create sustainable, green environments. The US is slower in making the shift to MTC compared to other countries, but has begun some construction plans for tall timber buildings in Manhattan, NY, and Portland, OR. Learn more about How to Create Infrastructure with Sustainability and Resilience in Mind, or read New Product Architects and Structural Engineers Will Love.
REFERENCES:
- Kremer, Paul., and Symmons, Mark. "Mass Timber Construction as an Alternative to Concrete and Steel in the Australia Building Industry: A PESTEL Evaluation of the Potential." International Wood Products Journal, Volume 6, July 1, 2015. https://www.researchgate.net/publication/281199721_Mass_timber_construction_as_an_alternative_to_concrete_and_steel_in_the_Australia_building_industry_A_PESTEL_evaluation_of_the_potential
2. "2021 IBC, 2018 Group A, Tall Mass Timber Proposals Review Guide." International Code Council (ICC) Review Guide. https://www.awc.org/pdf/tmt/TMT-ProposalsReviewGuide-180308.pdf
3. DeStefano, Jim., and Epp, Lucas."Mass Timber Engineering." STRUCTURE Magazine, August 2019. https://www.structuremag.org/?p=14792
4. Baldwin, Eric. "Timber Tutorial: How to Build Taller with Wood." Arch Daily, November 8, 2019. https://www.archdaily.com/926684/timber-tutorial-how-to-build-taller-with-wood
5. DeStefano, Jim., and Epp, Lucas. "Mass Timber Engineering." STRUCTURE Magazine, August 2019. https://www.structuremag.org/?p=14792
6. Baldwin, Eric. "Timber Tutorial: How to Build Taller with Wood." Arch Daily, November 8, 2019. https://www.archdaily.com/926684/timber-tutorial-how-to-build-taller-with-wood
