A Developer’s Guide to Mass Timber for High-Rise Residential
As interest in and demand for mass timber accelerates, and recent code changes allow for mass timber in taller buildings, developers are exploring mass timber solutions for high-rise residential structures. Many of mass timber’s benefits, including its lower carbon footprint, are well-documented but considerably less information is available to accurately analyze the cost of a mass timber building.
That’s why in late 2020, ZGF, BTY Group, Axiom Builders, and WSP Canada, along with building code and acoustic experts, set out to answer the question, “what will it cost to build my high-rise project with mass timber in our market?”
The resulting demonstration study, “Making Mass Timber Work for High-Rise Residential in BC,” aims to narrow the data gap by assessing the viability of mass timber in high-rise residential. The study compares the cost, construction methods, and schedules of a typical concrete high-rise in Vancouver, BC to a theoretical mass timber option.
The study utilizes the ZGF-designed and Axiom Builders constructed, University of British Columbia Georgia Point 14 Storey multi-family residential project as the V1 base building. The Cast-in-Place reinforced concrete building serves as a good comparison for the Vancouver, BC market of residential towers ranging between 12-18 storeys.
Study Approach
The group created virtual models and 4D construction simulation models, of the cast-in-place base building (V1) and conceptual models of a theoretical mass timber building for side-by-side detailed comparisons. Initial analysis led to the exploration of two conceptual mass timber options: a hybrid model with mass timber floors and CIP core (V2), and a prefabricated hybrid building (V3). For each of the three options, the group sought to answer the following questions:
- Cost: What are the cost considerations for mass timber?
- Code: What are the code implications for mass timber?
- Schedule: How does a mass timber schedule compare to that of reinforced concrete?
- Growth: Can mass timber high-rise residential be delivered at scale in the BC market?
4D construction simulation models of a cast-in-place base building (V1), a hybrid model with mass timber floors and CIP core (V2) and a prefabricated hybrid building (V3).
The future of mass timber will be part of a complete prefabrication concept. We see cost premiums decreasing and schedule gains increasing with expanding industry maturity in prefabrication.
Taking Mass Timber to New Heights
Designing and building with mass timber involves trade-offs beyond cost and schedule. Effective collaboration among design, consulting, construction, and fabrication teams from the start is critical to success, as is setting approach early. The study presents seven key recommendations for owners and project teams considering mass timber.
1. Design for 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, Not 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 in the BC market.
3. Stay with the method you choose: A design developed to maximize the benefits of reinforced concrete buildings does not translate to mass timber for cost competitiveness and adaptable unit design. Switching from reinforced concrete to mass timber (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 Off-Site Fabrication: Further testing of materials and assemblies need to be completed to allow codes to adapt to mass timber and steel hybrid buildings.
5. Integrate, Prefabricate, Coordinate to Accelerate Schedule: Designing structure and envelope systems to maximize off-site prefabrication 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. Evolving Building Philosophy: The industry needs to shift its philosophy from “on-site building” to “on-site assembling” to be sustainable as prefabricated mass timber construction gains market share. This shift puts more emphasis on skilled designers and less emphasis on skilled labor.
We compared the cost of building a 14-storey residential tower using mass timber to that of an existing, equivalent 14-storey residential concrete tower in Vancouver, BC. Image: UBC Georgia Point & Oakwood designed and constructed by ZGF Architects and Axiom Builders.
Discover the Full Report
The 2021 International Building Code change to allow mass timber for buildings up to 18 storeys is certain to accelerate demand for mass timber in both the U.S. and Canada. Lessons from this demonstration study suggest an exciting future for mass timber high-rise buildings at scale.
To learn more, including a detailed cost comparison and prefabrication recommendations, download a full copy of the study.
Mass Timber’s Transformation
