Few would argue against the interior and exterior esthetic appeal of a mass timber building. The warmth of the natural and varied hues pleases the eye and enhances the “feel” of interior spaces.
Many consider mass timber construction (MTC) as an answer to the construction industry’s global challenge to reduce GHG and CO2 emissions, versus traditional steel and concrete. However, as more MTC projects are completed, there is an increased understanding about the design and construction implications and how to use wood to its best advantage.
Yet, it appears that steel and concrete will continue to have an important role to play. For example, designers imagining buildings solely with MT beams, floor slabs and columns run into issues concerning span limitations, beam depths and ceiling heights. These combine to impact the layout of useable interior space.
“What had been envisioned as a pure timber solution has become a hybrid solution,” said Carol Phillips, a partner with Moriyama and Teshima Architects. It’s a path more designers are willing to embrace.
During the recent Buildings Week, Phillips outlined innovative solutions her firm developed through lab testing while designing The Arbour for George Brown College on Toronto’s waterfront, due to begin construction next spring. The Arbour is a joint venture between Moriyama and Teshima Architects and Acton Ostry Architects.
For example, reduced beam depths and higher ceilings were made possible by combining thinner wood/concrete composite floor slabs with what Phillips called “slab bands.” These will allow spans between columns to exceed nine metres while also reducing ceiling heights. Solutions like this not only improve interior layout flexibility but offer developers the potential to add an extra floor for a given overall building height, a factor in urban areas where municipal height restrictions exist.
Many of the projects either completed or in the planning stage have been for either government or educational entities. However, Phillips says it is vital that MTC move beyond demonstration projects and deliver strong economic arguments to commercial developers.
“How do you overcome this when mass timber comes at a premium over steel or concrete?” asks Phillips.
“One answer are projects that reduce operational costs and increase value not only from reduced operational costs but the possibility to draw revenue by providing a quality and attractive tenant space, which will attract a higher rent.”
However, that’s a long-term argument. What about upfront costs? Suggestions have been made that MTC can be less expensive and faster to build than traditional stick, concrete or steel.
In fact, Brock Commons Tallwood House at the University of British Columbia is often cited as an example of both savings in time and money during construction. The 18-storey student residence was the tallest mass timber structure in the world when it opened in 2017.
According to CadMakers, the digital twin development solutions team that created fabrication models for the project, Tallwood House was delivered 3.5 months ahead of schedule and several million dollars less than the estimated costs of traditional construction methods.
However, Mark Gaglione and Vincent Davenport of EllisDon Construction, say MTC savings are not straightforward.
“We always look at the total construction cost. It’s not a simple matter like taking out the concrete number and putting in the wood number,” they told their audience at Buildings Week.
For example, finishing costs are usually lower than concrete, whereas insurance costs during construction are higher. There are also soft costs associated with seeking alternate building code solutions when an MTC design doesn’t fit into existing regulatory frameworks. Overall, Gaglione and Davenport say that, in their experience, a five to 10 per cent overall cost premium should be expected.
As for time, the sequencing of assembly varies from project to project. Among other factors, do assembly logistics permit two cranes onsite, allowing the steel or concrete core to be assembled alongside the outer timber structure, for example? Even then, the additional cost of operating two cranes must be considered.
As interest in MTC increases, so will the understanding of its potential, both structurally and economically.
John Bleasby is a Coldwater, Ont.-based freelance writer. Send comments and Inside Innovation column ideas to firstname.lastname@example.org.