Timber can deliver the same, if not lower, costs than steel and concrete when designed to equivalent performance standards. That is according to a new study led by WSP, McCallumSather and ArcelorMittal, unveiled at The Buildings Show in Toronto, Canada, late last month.
The team modelled a 12‑storey, 287,000‑square‑foot (26,650‑square‑metre) L‑shaped residential tower in three materials — green steel, low carbon concrete and mass timber — to test how each performs on a level playing field.
The session, The Triple Bottom Line of Structural Materials: Cost, Speed and Life Cycle Assessment, brought together Brant Oldershaw of WSP; Willems Ransom of mcCallumSather; Matthew Winters of ArcelorMittal’s Steligence programme; and Mike Cortese, ArcelorMittal’s principal sustainability projects manager.
Using ArcelorMittal’s Steligence initiative, WSP and mcCallumSather developed three functionally equivalent digital models — one for each structural system — with RJC and MTE contributing structural details. “We were not designing a building, but a case model,” Ransom said. “It was normalised for the market, but optimised for no single solution. It was flexible, with a typical building envelope and massing.”
The team compared structural weight, cost, construction speed and environmental impact. Winters said the study initially focused on steel and concrete but expanded as interest in timber accelerated: “Originally, we only compared steel and concrete frame systems. Now, we added a mass‑timber scenario, where it’s more challenging to ensure functional equivalency.”
“Mass timber is more spatially intensive and lends itself to certain spans,” Willems added, “but we maintained the same functional floor plan as much as possible across the various options.”
Oldershaw said the baseline remained consistent across all three systems: “We kept it as generic as we could, with commonalities like concrete foundations and cast‑in‑place concrete for stairwells.”
Environmental performance was assessed through full life‑cycle analysis using third‑party‑verified Environmental Product Declarations (EPDs), with global warming potential (GWP) as the primary metric: “We used One Click LCA software to compare three functionally equivalent buildings,” Cortese said. “With the EPDs, we ‘sourced’ local products where possible. The number of EPDs available is growing exponentially, which makes this work easier to do and more accurate.”
Oldershaw said the results challenged expectations: “I thought there’d be a bigger gap on LCA.”
The study compared ArcelorMittal’s XCarb recycled and renewably produced steel; a general‑use low‑carbon (GUL) concrete mix; and a hybrid mass‑timber system using British Columbia glulam and Ontario CLT. The timber scheme was modelled using point‑supported cross‑laminated timber slabs, glue‑laminated timber columns, and a combination of glue‑laminated timber and steel wide‑flange sections to achieve the required spans and load paths. The GWP results were remarkably close — concrete slightly higher, followed by mass timber, then steel — with all three meeting the Toronto Green Standard.
“The close results surprised me,” Cortese said. “It came down to consistency in philosophy, design and material selection.”
Winters said the modelling underscored a broader lesson: “As we tried to reduce embodied carbon for this case study, we realised when we’re designing well and using materials to their strengths, we can hit our sustainability targets with any material.”
Cost differences were also narrow: steel at $3,107,500, concrete at $3,121,500 and timber, surprisingly, at just $3,011,000: “We put timber into an unusual context with this project,” Ransom said, “but realised it’s becoming a more equitable option that can be comparable to steel and concrete.”
Where the systems diverged, however, was in construction speed.
After identical timelines for foundations (40 days) and cladding (70 days), timber proved fastest at 113 days for the structure, followed by steel at 157 days and concrete at 190 days.
And reflecting on the process, Ransom said the collaboration highlighted both the opportunities and the complexity of modern material selection. “LCAs are easier to produce, and there’s better software, but that leads to a much more difficult decision‑making process, which is positive,” he said.
“We used to design by rules of thumb. Defining the critical factors of impact demands a different level of investigation in the design process, which is greatly enhanced through collaboration with industry partners. We have data to mine now, but it’s changing at a rapid pace. So, we need to start to define processes to streamline decision‑making. Integrated Project Design (IPD) is an ideal scenario, but takes a lot of time and people!”
- To learn more about the study, click here for On-Site Magazine’s coverage from The Buildings Show in Toronto, Canada.
