Technical: Mass Timber Through a Life Cycle Lens
In 2020, I led a studio at the University of Toronto’s John H. Daniels Faculty of Architecture, Landscape and Design that asked: How can we halve the carbon emissions of buildings over the next decade? Our collective research focused on strategies for benchmarking and reducing embodied carbon, using a series of real-life Toronto multi-unit residential buildings as case studies.
Towards Lower-Carbon Materials
The Ha/f Research Studio has since worked to build on this initial research. Working with the City of Toronto’s Green Standards Team and Mantle Development with the support of The Atmospheric Fund (TAF), we are currently developing embodied carbon benchmarks for Part 3 buildings across Ontario. The ongoing study involves stakeholders representing the full spectrum of our industry and included nearly 50 voluntarily submitted project life cycle assessments (LCAs). This intake reveals that LCAs are being conducted across Ontario, and are being performed throughout the design and construction process. The number of respondents familiar with the tools suggests that the market can support this type of analysis.
As part of the study, the City’s team requested an assessment of two active, City-owned projects to understand their embodied carbon and find potential reductions, and to understand how future policies should align with design phases and existing planning submission milestones. Both projects—the Western North York Community Centre and the Toronto Paramedic Services Multifunctional Paramedic Station—are 2021 Canadian Architect Award recipients, and have had embodied carbon and operational performance as key drivers of their designs from the outset. Working directly with the City’s project managers and the architectural teams, Ha/f produced detailed LCAs and reduction recommendations that targeted material specification changes, given that each project is nearing design completion.
The Paramedic Services Multifunctional Paramedic Station’s LCA revealed six main sources of upfront emissions that could be improved upon, without requiring significant redesign or additional construction cost. Given their relative impact, the floor slab insulation, concrete mix, and floor sealant were obvious places to focus. Of note is the project’s CLT roof structure—the use of mass timber has served to reduce the project’s total embodied carbon, resulting in a value of 380 kgCO2e per m2—a figure on the low end of our benchmarking spectrum.
We circled back to the client and architect teams with the suggestions shown in Figure 2. Through straightforward material and specification swaps, the project could avoid upwards of 800 tonnes of CO2e—or roughly 44 years of Canadian per capita emissions. Following a brief review period, the architects responded that 5 of the 6 changes would be implemented, and that initial costing feedback stated the changes were cost negligible. Forty-four years’ worth of emissions avoided through a two-week study reveals, to me, just how simple the first steps towards the radical reductions required of us are, and that substantial reductions are immediately achievable through existing, readily available options.
Mass Timber and the Impact of Biogenic Carbon Sequestration
Building further on last year’s studio, I wanted to broaden Ha/f’s understanding of embodied carbon in contemporary construction through a focus on the “it” material for carbon reductions: mass timber. Given the surge in attention that mass timber has received, this year’s students took on case studies to better understand the promise—and limitations—of this family of materials. How does the embodied carbon footprint of mass timber buildings compare to the largely concrete structures of the previous year’s studio, which averaged 505 kgCO2e/m2? To expand this question across geographies, we assessed the structure, envelope and finishes of mass timber projects from Sweden, the UK, Ontario, Washington, and Oregon, engaging many of the world’s leading mass timber architects in the process.
Initially, the carbon advantages of mass timber were not as evident as expected. This year’s research study set averaged 443 kgCO2e/m2 for new construction, or roughly 90% of last year’s study set. A caveat for this comparison is that the mass timber projects from this year’s study are largely commercial uses, and as a result have far less internal walling, which serves to reduce their totals in comparison to last year’s multi-unit residential buildings. Ultimately, the embodied emissions associated with the extraction, manufacturing, erection, occupation, and ultimately disposal of either building stock are near equal.
However, if carbon storage via biogenic sequestration is taken into account, the net average drops dramatically to 192 kgCO2e/m2—roughly 40% of typical construction. There is currently a lot of debate about how best to account (or whether to account at all) for carbon storage in LCA reporting, due in large part to the complexities of forestry practices around the world, and the unknowns of a building’s ultimate service life. Our studio visited local operations to better understand the seedling-to-sawmill process. This experience prompted the students to investigate the sources of timber across the range of projects, an exercise that enabled a greater appreciation for the impacts of forestry at-large, and a keener sense of the challenges related to the lack of reliable data.
Overall, it became clear that responsibly sourced wood, when accounting for bio-sequestration, can be a low-carbon solution for structure, envelope, and interior finishes. Beyond wood, the re-emergence of less processed, organically based materials also offers promising carbon-storing options for structure, envelope, and finishes.
Envelopes: Embodied Carbon Meets Thermal Performance
Focusing on envelopes, this year’s case studies stood in stark contrast to the highly emissive, thermally low-performing, aluminium-based unitized glazing systems of the multi-residential buildings that we examined last year. The envelopes of this year’s study reveal substantial upfront and operational emission reductions achieved by (a) reducing window-to-wall ratios, and (b) incorporating mass timber into the façades themselves. These savings are further amplified by a whole-life carbon assessment, given the comparatively short lifespan of the unitized systems. Envelopes that achieve high R-values and also serve as carbon sinks offer our profession a promising direction of travel.
Geography Matters with Mass Timber
In comparison to other materials, the provenance of mass timber has significant and disproportionate impacts on the resulting global warming potential (GWP). Where mass timber supply and manufacturing was regionally abundant, the footprint of the timber was roughly 10-15% less than in projects where the engineered material was sourced trans-continentally or internationally. Of the four Toronto mass timber projects, only one used wood sourced in the province
of Ontario, while all CLT and glulam elements were still imported from either European or western North American sources.
Beyond the impact of continental transportation, the location of processing is a significant factor in how emissive one product is relative to another. As a result, industry-wide generic Environmental Product Declarations (EPDs) can be significantly different to manufacturer-specific EPDs for the same product class. A close examination of EPDs early in a project’s development can help ensure the eventual sourcing of timber that is sustainable, low-impact, and importantly, available. In the case of the Catalyst Building, we had two LCAs to compare: one conducted by the Carbon Leadership Forum in 2019 and ours in 2022. The delta between generic data and that of the eventual supplier resulted in a 40% increase of the project’s total embodied carbon. Variations between manufacturer emissions relate in large part to the carbon intensity of the power grids that their facilities sit upon. A sawmill in Alberta emits roughly eight times that of one in Washington State; as a result, a tree cut in BC feeding into either mill would carry much higher embodied carbon if cut and dried in Alberta. Geography matters.
A Whole-Life Carbon Perspective
Finally, the benefits of mass timber are most significant if we are able to take a whole-life carbon perspective that accounts for upfront material emissions, reduced life-cycle operational emissions, and future disassembly and reuse of structural materials. Marrying the reductions afforded by mass timber’s biogenic storage capacity with high-performing, low-GWP façade systems can result in buildings with significantly reduced footprints upfront, as well as over the life of the project. Whether or not we build in mass timber, we need to take a whole-life carbon view to ensure decisions made to reduce operational emissions are not resulting in significant, unintended upfront emissions.
Any further delay in concerted global action will miss a brief and rapidly closing window to secure a liveable future.
—Hans-Otto Pörtner, co-chair of IPCC working group 2, February 28, 2022.
The time is now. Our entire industry needs to adopt a whole-life approach to the buildings we design. We need to address the magnitude of emissions associated with our daily design and specification decisions. As evident in the examples above, a short investigation into a material class’s provenance could result in the avoidance of several lifetimes’ equivalent of emissions.
Canadian architects, engineers, and planners have a disproportionate responsibility when it comes to addressing climate change, and only by taking a whole life view will we be able to balance reductions in operational emissions with reductions in embodied carbon emissions.
We are here to support your practice, institution, or municipality to take this on. We look forward to discussing this research and its findings with you, at your request.
The Ha/f Research Studio was conducted at the John H. Daniels Faculty of Architecture, Landscape, and Design. It was led by Adjunct Professor Kelly Alvarez Doran, co-founder of Ha/f Climate Design, and Senior Director of Sustainability and Regenerative Design at MASS Design Group.
The project team included graduate students Saqib Mansoor, Bahia Marks, Robert Raynor, Shimin Huang, Jue Wang, Rashmi Sirkar, Ophelia Lau, Huda Alkhatib, Clara Ziada and Natalia Enriquez Goyes.
Project partners from the architectural community included White Arkitekter, Waugh Thistleton, Hawkins/Brown, Lever Architects, Michael Green Architects, Bucholz McEvoy Architects, ZAS, MJMA, Patkau Architects, BDP Quadrangle, and Moriyama & Teshima Architects.