Building with wood has its benefits. We know that timber sequesters carbon, promotes health and wellness when exposed in buildings, and is easier to recycle than traditional building materials. But with CLT, LVL, NLT and other forms of mass timber materials still in their infancy in some jurisdictions, the cost-benefit of using wood for the construction of larger towers, those 12-to-18 storeys tall, has come into question.

A Canadian study, conducted in partnership with WSP Canada, BTY Group, Axiom Builders and ZGF, sought to understand the comparative building costs using mass timber products versus other forms of building materials. The report only conducted a like-for-like comparison, using the fluctuating cost data experienced in the mass timber supply chain in the British Columbia market, more specifically Vancouver.

“Our goal was to assess the viability of mass timber for this product type in BC by comparing the cost, construction methods, and schedules of a typical concrete high-rise in Vancouver to those for the same building using mass timber as the principal structural material. To undertake the study, the group created virtual models of the base building and conceptual models for side-by-side detailed comparisons.”

Located on Canada’s Pacific coast, the province has the country’s largest wood supply, and manufacturers of mass timber products, but supply issues created by the pandemic caused prices to jump significantly. This study considers those price and supply variables, and includes data that can be modified to reflect local material costs.

While the report was focused on a single major metropolitan market, the report’s findings are applicable to markets around the world for understanding the cost variables, benefits, and additional factors that create unnecessary risk in the project’s overall development:

1. Design for either timber or concrete, not both
   
   Combining prefabricated structural materials with built-in place methods for the building structure and envelope produces only a marginal net increase in any potential efficiencies. An over-arching construction philosophy must be chosen early on and remain consistent through the design of all aspects of the building – architecture, structure, and systems.
   
   
2. Design for Manufacturing and Assembly (DfMA), not just construction
   
   Optimized design for mass timber, increased off-site fabrication, appropriate code changes and expansion of prefabrication trades and suppliers will accelerate development of mass timber’s cost-competitiveness and maximize the available benefits.
   
   
3. Stay with the method you choose
   
   A design developed to maximize the benefits of reinforced concrete (RC) buildings does not translate to Mass Timber (MT) for cost competitiveness and adaptable unit design. Switching from RC to MT (or vice versa) at any stage past early conceptual building design and massing is inefficient – and not recommended.
   
   
4. Adapt codes to support mass timber and offsite fabrication
   
   Current codes need to adapt to mass timber and off-site fabrication methods. Further testing of materials and assemblies needs to be completed to allow codes to adapt to mass timber and steel hybrid buildings.
   
   
5. Integrate, prefabricate and coordinate to accelerate schedule
   
   Designing structural and envelope systems to maximize off-site pre-fabrication of all aspects of timber hybrid buildings, including the lateral system, will lead to faster on-site assembly, higher quality control and fewer trades involved. Any prefabricated design for structure and envelope systems requires significant coordination and procurement in pre-construction.
   
   
6. Schedule savings remain theoretical
   
   Anticipated holistic schedule savings attributed to high-rise mass timber buildings have yet to be thoroughly proven in the field.
   
   
7. The industry’s building philosophy must shift
   
   The industry needs to shift its philosophy from “on-site building” to “on-site assembling” to be sustainable as prefabricated gains market share. This shift puts more emphasis on skilled designers and less emphasis on skilled labour.

These seven key findings from the research conducted led the group of companies to create 10 recommendations for tall mass timber development:

1. Optimize design to maximize benefits of using mass timber and prefabrication methods. This does not necessarily have to mean box-like, rectangular building forms.
   
   
2. Adopt modern methods of construction and DfMA holistically to amplify the inherent properties of prefabricated timber – and accelerate innovation in the design of an efficient and prefabricated lateral system.
   
   
3. Focus on developing mass timber steel hybrid buildings. A steel lateral system maximizes potential for significant schedule savings.
   
   
4. Prefabricate the lateral systems so that they are modular like the gravity system of columns, connectors and CLT panels. Consider prefabricated exterior envelope systems and balconies for optimal construction efficiencies.
   
   
5. Space and unit planning in a prefabricated mass timber building should be more “structure forward” than in a comparatively flexible concrete building. Address the floor plate concept early and more systematically to avoid inefficient constraints of the building footprint and materials.
   
   
6. Adopt extensive offsite pre-fabrication throughout the project for its broader benefits: faster construction times, better quality products and finish, and less waste.
   
   
7. Evolve local codes to accept building materials and processes that maximize mass timber and pre-fabrication benefits for the design and construction of buildings exceeding 12 storeys. Focus on 12-18 storey segment.
   
   
8. Upskill local mass timber construction market on prefabrication methods to deliver schedule advantages.
   
   
9. Educate insurers about mass timber building performance, to create a new classification for buildings utilizing mass timber.
   
   
10. Develop a comprehensive moisture management plan early in project planning. 

The findings and recommendations revealed in the report provide a greater understanding of how to increase the adoption of mass timber by recognizing the challenges and opportunities for doing so. The report does not factor in the environmental benefits of this type of construction, and depending on how the project owner values those benefits, from a monetary perspective, the case for increased adoption of mass timber construction becomes even greater.

For more information on mass timber construction, visit our Mass Timber Hub or reach out directly to William Johnston, Senior Director, Structures, WSP Canada.