Nov 17, 2017
BY:
THEME: Sustainability

Mass Timber: A Primer and Top 5

Wood is gaining momentum as a modern construction material. Wood is also one of the oldest materials known to us, yet we are still expanding the range of structural and design possibilities of this sophisticated material through innovations in wood technology and advances in engineered wood such as mass timber. The growing field of mass timber is a fundamental disruption of conventional concrete-and-steel approaches to building design and construction.

Instead of limiting wood to low-rise, light frame application, we can now reimagine wood as an advanced structural system that produces communities with greater speed, efficiency and resilience.

As early adopters of mass timber, Perkins+Will pioneered several precedent-setting mass timber projects and research projects, and co-authored technical guides and stakeholder surveys in the spirit of a sharing our best ideas with the larger design and construction industry.

Exterior CLT canopy, Earth Sciences Building (ESB), Vancouver BC, Canada (Photo Credit: Martin Tessler). At its time of construction, ESB was the largest panelized wood building and largest application of CLT in North America.

Curved NLT panel prototype, fabricated on a 5-axis CNC at Autodesk BUILDSpace

The recently released Nail-Laminated Timber (NLT) Design + Construction Guide (co-authored by Perkins+Will and Fast+Epp), is a comprehensive technical guide about NLT as a product, and details key design and fabrication considerations through built project examples.

The Survey of International Tall Wood Buildings (left), Technical Guide for the Design and Construction of Tall Wood Buildings in Canada (middle), and the Nail-Laminated Timber Design and Construction Guide (right), are some of the recent publications co-authored by Perkins+Will in an effort to share our design expertise and market research.

In order to understand the relevance of this guide and the exciting shift it signifies in current design thinking, it is important to gain a fundamental understanding of mass timber and its unique advantages.

WHAT IS MASS TIMBER?

Mass timber describes engineered wood products in which smaller wood elements are glued, laminated or mechanically fastened to create a larger structural wood panel. Unlike light-wood frame construction (which uses dimensional lumber such as 2”x4”, 2”x6” etc. to create a space frame through mechanically fastening systems), a mass timber structure is made of engineered wood panels assembled in a panelized or post-and-beam system using sophisticated connectors and precise digital fabrication techniques.

Since several existing resources such as naturallywood.com and reThinkWood.com provide in-depth information and training on mass timber, we will highlight some salient facts about mass timber that demonstrate its unique advantages over conventional building approaches.

1: The oldest wood building is 1400 years old (and is still standing)

Wood was often the material of choice for our ancestors, as showcased by the Horyu-ji temple in Nara, Japan. Constructed in the 7th century, this temple is the oldest surviving wood building in the world. Perhaps a testament to the durability of materials crafted by nature, this 122’ tall structure continues to survive in a seismic zone and wet climate environment1, 2.

In a more recent historical context, heavy timber buildings from the early 20th century, such as the Landing and Leckie buildings in Vancouver, and the Baker & Hamilton Building in San Francisco, continue to stand the test of time, and thrive as modern working and living spaces.

2: There is more than CLT.

Advances in wood technology in the 1990s yielded the first cross-laminated timber (CLT) panel in Europe3. While CLT is one of the more popular mass timber products and is well known for its efficiency and double-span capability, other products that have emerged in the market demonstrate a wide range of structural strength and design flexibility, and allow us to build faster, leaner and better.

Currently, eight different types of mass timber products are available in North America. This includes mass timber products made by gluing or mechanically fastening dimensional lumber or some variant of it – such as cross-laminated timber (CLT), Glulam or glue-laminated timber, nail-laminated timber (NLT) and dowel-laminated timber (DLT); as well as structurally composite lumber products made by adhering layers of wood strands or veneers – such as LVL (laminated veneer lumber), LSL (laminated strand lumber) and PSL (parallel strand lumber) and the recently introduced MPP (mass ply panel).      

Mass timber products currently available in North America.

3: Mass timber is resilient

Mass timber’s unique properties allow for better performance in seismic conditions when compared to conventional concrete structures. This is because seismic forces are directly proportional to a building’s weight, and mass timber weighs only about half of concrete. In addition, mass timber systems are comprised of ductile connections and redundant load paths, which offer greater resistance against earthquakes. With further advancements in high-performance mass timber systems (such as the rocking wall system recently tested in Oregon4), mass timber has the potential to create post-disaster level buildings and increase our collective resiliency against natural disasters.

4: Mass timber is a natural insulator

Wood is a natural insulator. Wood has an insulation value about ten times greater than concrete, and 400 times greater than steel. In addition, the thickness of mass timber panels such as CLT offers greater thermal mass, which allows us to reduce the required amount of insulation material without compromising on overall building performance. The precise and digitally controlled fabrication process of mass timber offers exciting possibilities to pre-fabricate exterior wall assembles in a controlled factory setting, and meet higher air tightness standards and building performance targets.

By utilizing a structure that is made of renewable resources, is a carbon sink, and is inherently more energy efficient, we can significantly reduce our resource footprint and shift towards responsible material and construction choices that directly respond to climate-change mitigation strategies.

5: Mass timber is healthy

Buildings have a profound impact on occupant health and well-being. We spend approximately 90% of our time indoors5, essentially disconnected from natural outdoor environments that are known to have calming and restorative effects on us. Wood-based interior environments, however, have demonstrated biophilic benefits for its occupants. Recent studies indicate that stress levels are lower in wood-based interior environments compared to the conventional white gypsum wall interiors5. Exposed mass timber structures offer a unique psychological and physiological advantage compared to conventional steel and concrete systems. In addition to saving on interior material finishes, exposed mass timber structures allow us to bring nature back into our interior environments with the warm glow of wood. For more information on how mass timber compares with other structural materials, visit Perkins+Will’s material transparency website. Ongoing material research will refine the material profile of engineered wood products and allow us to develop cleaner, healthier buildings.

The above five key facts only offer a preliminary glimpse into the range of benefits and opportunities available with mass timber systems. Stay tuned for future blogs that explore mass timber and its connection to climate change leadership, building code changes and fire design approaches, digital fabrication techniques, and more.

As designers, we have a significant role in creating sustainable, healthy and resilient environments. Mass timber offers a fundamental shift in design thinking and a holistic approach to responsible material choices.

References

  1. Wood’s Heritage, Canadian Wood Council (http://cwc.ca/design-with-wood/durability/woods-heritage/)
  2. The Case for Tall Wood Buildings, by Michael Green and Eric Karsh, 2012.
  3. CLT Handbook, edited by Sylvian Gagnon and Ciprian Pirvu, 2011.
  4. Mass Timber Shaking Things Up, Tall Wood Institute, http://tallwoodinstitute.org/news/mass-timber-shaking-things
  5. Wood and Human Health Series, Issue 1, David Fell, 2010.

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