Canadian CLT Handbook, 2019 Edition
Edited by Erol Karacebeyli and Sylvain Gagnon. (FPInnovations, 2019)
Tall Wood Buildings: Design, Construction and Performance
By Michael Green and Jim Taggart (Birkhauser, 2020)
The advantages to building with mass timber are clear: compared to steel or concrete, wood is a renewable resource with the potential to sequester carbon. This makes it a construction material of increasing import in the era of anthropogenic climate crisis.
Two recent Canadian publications help equip architects and engineers in using mass timber. The Canadian CLT Handbook, published by forest products research organization FPInnovations, is a two-volume reference manual compiling technical information on cross-laminated timber. (A parallel US edition is also available.) Tall Wood Buildings, by Vancouver-based architect Michael Green and educator Jim Taggart, focuses on the potential for mass timber’s use in mid-rise and high-rise buildings in urban centres. “Tall Wood buildings represent the most practical, effective and environmentally responsible solution to the global housing shortage,” write Green and Taggart.
The CLT Handbook is edited by engineers Erol Karacebeyli and Sylvain Gagnon, and clocks in at 812 pages. Its peer-reviewed content delves deep into the construction and performance characteristics of cross-laminated timber, from manufacturing to structural and lateral design. Chapters are dedicated to particular aspects of CLT buildings and assemblies, including vibration performance, acoustic performance, and the lifting and handling of CLT elements. The comprehensiveness of this tome makes it, as the editors write, a “vital ‘how-to’ [of] information on CLT for the design and construction community, and [a] source of information for regulatory authorities, fire services and others.”
While a technical manual does not generally make for riveting reading, the material characteristics of CLT are key to understanding its performance. The material’s lay-up pattern, for instance, means that using wood species prone to shrinkage and swelling may produce unsightly gaps. A chapter on environmental performance dives into the particulars of life cycle assessment, and points to research limitations in current analyses. For instance, what additional carbon benefits or harm would result from not harvesting a forest for use in construction? The forest may continue to grow, but would also be subject to natural disturbances such as fires—a major source of greenhouse gas emissions.
One of the most important changes from the 2011 version of the CLT Handbook is an updated chapter on fire performance. The new edition accounts for the extensive research that has taken place in the past decade, with results showing “that CLT elements, with or without gypsum board protection, can achieve significant fire resistance, beyond three hours in some cases.”
As architects working with tall CLT buildings in Canada can attest, the process of reconciling CLT construction with existing building regulations can be onerous. A proposal has been made to include encapsulated mass timber as a new type of construction in the 2020 National Building Code of Canada—provisions that have already been adopted in British Columbia. If accepted, the authors note, CLT would then fall into the prescriptive framework of the code, and “this will facilitate the use of CLT elements in residential and commercial buildings up to 12 storeys.”
In the CLT Handbook, “design” is used most often to refer to engineering considerations, rather than aesthetic results. Accordingly, a good part of the two-volume set is filled with formulae and data tables that will be of principal interest to engineers. No matter: the Handbook is free to download, and well worth having on hand.
A more approachable primer is Tall Wood Buildings. This book opens with a well-illustrated run-down of the principles of building with mass timber products such as CLT, glulam, laminated veneer lumber, and dowel-laminated timber. The thoughtful assessment runs almost in parallel to the structure of the CLT Handbook—starting with the properties of wood, and building up to the factors affecting structural systems, building performance, and construction considerations.
The book then turns its focus to a series of 18 case studies (augmented from 13 in an earlier edition). They are helpfully grouped into different types of mass timber structures. Panel systems use regularly spaced, solid wall panels to carry loads, and are well-suited for housing. Frame systems carry vertical loads through interconnected sets of beams and columns, and are used for programs requiring larger interior spaces. Finally, hybrid systems use different material and structural solutions in combination, for a variety of architectural, structural, environmental or economic reasons.
Each case study is illustrated with diagrams, details and photos, often showing both the under-construction and completed buildings. Shigeru Ban’s Tamedia Head Office, for instance, includes an assembly sequence for the all-wood post-and-beam structure, a design inspired by traditional Japanese joinery. Oval (rather than circular) holes are used at the joints, ensuring that tie-beams cannot rotate, thus allowing them to absorb lateral forces.
Three Canadian examples also figure among the case studies—Perkins and Will’s Earth Sciences Building at the University
of British Columbia, Acton Ostry Architects’ Brock Commons Tallwood House on the same campus, and MGA | Michael Green Architecture’s Wood Innovation and Design Centre in Prince George, British Columbia. Such buildings have set precedents in the North American building context, laying the ground for further development of mass timber buildings.
As the CLT Handbook details, 37 percent of the world’s certified sustainably managed forests are in Canada; within Canada, 49 percent of forests are independantly certified. The potential for Canada to become a mass timber leader is tantalizing.
In the preface to Tall Wood Buildings, UK architect Andrew Waugh writes: “re-learning how to build in timber—and how to build tall with the new engineered timbers that the 21st century technologies allow—will be fundamental to our future.” This pair of books are invaluable to architects and students taking on that task.
Source: Canadian Architect