The 2015 change in the Ontario Building Code that permits wood structures up to six storeys and the resulting surge in the construction of these buildings, seems to indicate that there is considerable support for larger wood structures in Ontario, but for practitioners wanting to pursue a wood structure taller than six storeys, there has been very limited practical support. Mass timber products, for example, are not specifically defined as a distinct material in the current Ontario Building Code and it is these mass timber products that make tall wood construction possible.
Mass timber products are large-scale, engineered wood components that are similar in definition to solid timber but otherwise fall under the classification of all other combustible construction materials. Since the building code has historically required tall buildings to be built of non-combustible construction, using any combustible material, including mass timber, for structural purposes was not an option in Ontario for a long time. Fortunately, things have now changed.
Since the 2006 version of the Ontario Building Code came into effect, architects in Ontario have been freed from the compliance constraints of a single acceptable solution (prescriptive path). In 2006 the Ontario Building Code introduced a two-volume compendium that includes clause by clause descriptions of objectives and functional statements that support a new performance path approach to meeting the requirements of the building code. This performance path approach allows architects to submit alternative solutions to the Authority Having Jurisdiction (AHJ) that demonstrate they have met the intent of the Building Code’s objectives and functional statements when they are not following the traditional prescriptive requirements described. The alternative solutions process has been in place for a decade and, although it may not have been imagined ten years ago, the performance path included in Ontario Building Code 2006 was the first step toward tall mass timber structures in Ontario.
The recently released Ontario’s Tall Wood Building Reference, prepared jointly by the Ministry of Natural Resources and the Forestry and the Ministry of Municipal Affairs, is making it easier for project teams to consider a mass timber structure for tall buildings. This comprehensive technical reference can assist architects and engineers with the development of an alternative solution for a mass timber structure, to be submitted to Building Officials for acceptance, using the Ontario Building Code’s above noted performance path. All architects considering mass timber structural systems and practicing in Ontario should review this document in detail; it includes a thorough background of mass timber systems and a detailed explanation of the alternative solutions process. Beyond the first few chapters, the reference focuses on the two major elements that need to be considered in an alternative solution for a mass timber structural system: fire safety design and structural design. These chapters include in-depth descriptions of the engineering considerations that must be addressed as the design team develops the project. They are particularly helpful since it is very important that the project architect, who will ultimately seal the building permit drawings, has a strong understanding of, and confidence in, the technical engineering concepts.
Bringing together the right team for a project is equally as important as developing the right technical details, and the team starts with the client. It is still early in the implementation of tall mass timber structures in Ontario, so the Client will need to be open to considering this construction method as an option. Having done proper research, an architect should be in a position to present the option to the client and determine if it is the right solution for the project. All the standard project considerations are likely to be in play (schedule, sustainability goals, aesthetics, budget, programmatic requirements), so the architect should be prepared to clearly describe benefits of mass timber construction to the client; carbon sequestration, speed of construction, and reduced structural weight, and drawbacks; slower design schedule due to the alternative solution process, public misperceptions of mass and lack of experience of the trades. Assuming there is no project specific reason to eliminate wood as a potential structural system, the client’s openness to construct a tall mass timber building is crucial.
Aside from the client, as the prime consultant, the architect should be confident that all the other key individuals on the team will help create a successful project. A structural engineer who is comfortable with mass timber products, kntowledgeable regarding current tested techniques, and can speak with some authority on differences between structural considerations for mass timber and traditional systems, will be a significant benefit to the project team during meetings with building officials. Ensuring a fire engineer is part of the team in the preliminary stages of the project is also very important. Working with the structural engineer, these two engineers will generate the bulk of the technical information required for the alternative solution submission and will provide key information to help navigate early structural design decisions. The fire engineer should have access to the results of fire tests that have already been completed and can identify if additional testing will be required for the fire protection strategies under consideration. Beyond the structural and fire engineers, the key individuals required on any given project will depend on the structural strategies considered, but will likely include an acoustic engineer, mechanical and electrical engineers, and potentially building envelope specialists. Each of these individuals will need to understand the subtleties that mass timber products bring to their respective disciplines.
Like most multi-disciplinary team projects, the design of a tall mass timber structural system will benefit from a strong integrated design process. The architect will need to be comfortable coordinating and leading this type of exchange, ensuring all disciplines are engaged and participating in the design decisions from the beginning. The first decisions will be to determine appropriate and available mass timber products (CLT, NLT, LVL, Glulam, etc.) and the preferred structural concept (post-and-beam, concrete cores or podium, shear system, etc.). These decisions will be heavily influenced by fire protection and acoustic strategies, and will lead to one of the most important architectural discussions: to expose the mass timber or encapsulate it? This discussion will likely be the most spirited, but it is important for all parties to understand the implications of exposing the structure. The decision to expose the wood affects the budget, the acoustic strategy, and ultimately the structural and fire protection requirements for the alternative solution. Ontario’s Tall Wood Building Reference can offer useful insight into this discussion. The current world’s tallest mass timber structure, Brock Commons – Tallwood House in Vancouver, is completely encapsulated. The strategy for this building was unabashedly to encapsulate the mass timber, and it offered many benefits, not the least of which was to simply ensure the building had the best chance of being built. The project architect, Russell Acton of Acton Ostry Architects, has discussed this convincingly at length. Yet there are also many projects where the structural wood system is left exposed. The Wood Innovation Design Centre in Prince George, British Columbia (previously the tallest mass timber building in Canada) and the T3 Office Building in Minneapolis, Minnesota developed systems that permitted exposed wood. Each team will need to evaluate its own priorities for each project.
Once the general strategies are established for the mass timber structure, the team may consider adding fabricators and suppliers to the process to determine physical dimensions and connection details, and ultimately to refine the budget estimates. Solutions for acoustic ratings and fire protection may be leveraged in the prefabrication process that is inherent in the production of mass timber materials. There is potential to pursue a design-build style arrangement by working directly with a mass timber fabricator as part of an integrated design process. Having knowledge of available materials and the costs to pursue certain design strategies will be invaluable to get client approval to move forward with the tall mass timber design solution. Developing strategies that simplify the alternative solutions submission will set the project up for success as it moves forward into the application process.
Once the structural and fire protection solutions have been clarified, it will be important to engage with the AHJ as early as possible. Open communication regarding the intention to submit an alternative solution for a tall mass timber structure will give the AHJ the opportunity to prepare their resources. Sharing a copy of Ontario’s Tall Wood Building Reference is advisable if they aren’t already familiar with it. The resources that AHJ will require to review and hopefully approve an alternative solution should not be underestimated. One Chief Building Official (CBO) has commented that they were very comfortable reviewing Alternative Solutions for specific Ontario Building Code, clauses or sub-clauses, but something as fundamental as non-combustibility of a structural system was daunting to consider at the outset, but once the process began it became manageable with his team in place. Experience suggests that most CBOs and their teams appreciate early involvement in the process, despite the additional effort it will require. Multiple meetings as a design team (architect, structural and fire engineers in particular) with the AHJ will be required to determine the intent of the alternative solution, the review process the AHJ is expecting, whether or not peer reviewers will be engaged (and assisting the AHJ to identify appropriate peer reviewers if necessary), and an overall timeline for the application and review. At least one meeting that includes the AHJ’s peer reviewers is also advisable. It is important to manage everyone’s expectations of the process, and to determine the AHJ’s key individuals and their roles, the submission requirements (including third party testing if not already available), and the submission review schedule.
In these early days of tall mass timber structures, securing approval of alternative solutions will not be without some challenges in many jurisdictions in Ontario. However, when considering a mass timber structural alternative solution submission, Ontario’s Tall Wood Building Reference is a key technical resource for the architect and the project design team. With its clear explanation of the alternative solutions process and the considerations needed for a submission to an Authority Having Jurisdiction, it should give design teams the confidence to navigate the submission requirements. In time, it will be easy to imagine mass timber structures as a common structural option for all tall buildings in Ontario.
Darryl Hood is a practicing architect in Ottawa with 20 years of experience. He is the Managing Director and Director of Sustainability at CSV Architects. He has collaborated with the Canadian Wood Council to research mass timber buildings in Ontario, working with Authorities having Jurisdiction to understand stakeholder concerns and requirements. Darryl is a contributor of Ontario’s Tall Wood Building Reference