OBC 2024: New Year, New Code
The 2024 Ontario Building Code (OBC) is coming into effect in just a few short weeks on January 1, 2025. This version of the OBC, broadly speaking, will be adopting the National Building Code of Canada (NBCC) model code from 2020, which means there are some updates!
Since we are structural engineers, we’ll be focusing on Part 4 changes, but there are other changes under Part 3 and Part 9 that will still impact future projects, such as an increased height of up to 18 storeys for encapsulated mass timber construction (EMTC)!
Don’t forget, current projects will still qualify under the 2012 OBC (amended) if they are submitted for permit prior to December 31, 2024! Even projects that show substantial completion prior to December 31 can qualify under the 2012 OBC so long as they are submitted for permit prior to March 31, 2025.
Many of the changes to the building code are relatively minor, such as updating to more recent CSA design stands. The new code also adds clarity on things like wind and snow loads for overhanging structures and solar panel installations, further enabling us to support architects, owners, and clients in providing sustainable design solutions. Three areas contain more distinct changes that will require some creativity and thought from structural engineers: importance categories, seismicity, and performance based design.
Importance Categories
The code breaks Part 3 buildings into four categories depending on their use. It’s not hard to imagine that some buildings need more stringent design criteria to remain operational during a major disaster, such as fire halls and hospitals, which get classified under post-disaster importance.
Until recently, post-disaster importance focused on the time immediately after a disaster, but did not directly address structures like sewage treatment, water storage, and water treatment plants. These structures are now explicitly classified as post-disaster structures due to their ability to prevent disease, provide sanitation, and ensure a secure water supply following disasters.
Seismicity
Anyone who has said that structural engineers aren’t creative hasn’t seen us working under the new seismic code. Engineers use seismic spectra, commonly denoted as Sa, to determine seismic loads, and differences in the spectra can be used to compare seismicity between regions. The 2024 OBC incorporates updated seismic data for Canada, leading to higher spectra and therefore higher seismic loading. Cities across Ontario typically see significant increases, such as roughly 75% increases in London and Kitchener, and 60% increases in parts of Toronto. While this shouldn’t significantly affect shorter buildings, it does start to add up in mid-rise to high-rise structures and could result in larger walls, larger footings, and higher reinforcing, but…
Fortunately, structural engineers have a knack for innovation, and we are working on ways to eliminate or reduce the impacts of the increased spectra. This involves techniques like capacity protected design, use of higher ductility systems, or dynamic analyses. These techniques can require creativity and skill on the engineering side but can result in more efficient structures despite these increases in seismicity. The seismicity could also be reduced through shear wave velocity (SWV) testing to more precisely determine soil properties, potentially reducing loads by up to 20%. One of the most impactful decisions is actually the building weight; lighter systems like steel, light framed timber, or mass timber could reduce weight by enough to offset or maybe even reduce the increased spectra!
Performance Based Design
What happens if an earthquake hits and your local hospital stays standing without major damage, but pipes break and flood, generators cannot run, and air cannot flow to operating rooms? Your hospital would shut down anyways! Unfortunately, this exact scenario occurred in the 90’s in California, which led to the development of Performance Based Design (PBD) principles that are increasingly common across North America. The basic aim of PBD is to prevent damage to mechanical or electrical systems by controlling movement under less severe, more common earthquakes than the design earthquake. The provisions in the new OBC will only apply to post-disaster and high importance structures like fire halls, hospitals, and community centres in moderate to high seismic regions. These new limits will allow critical infrastructure to stay functional under smaller earthquakes rather than shutting down due to damaged systems. The overall design impact of these would be generally small and only limited to the lateral system like shear walls or braced bays, but these small impacts can have major ramifications on post-seismic operation.
Training
Thankfully, our staff have already been hard at work redeveloping our internal library of spreadsheets, processes, and tools to incorporate the 2024 OBC code updates into our design practice. Many of our engineers also have experience in other provinces or territories that already use the 2020 NBCC model code, so it should be a relatively smooth adoption. Several of our Ontario projects that won’t be going for permit until the new year have even begun using the new loading. New codes bring new challenges, but our creative, skilled team of structural engineers and technologists are dedicated to solving them!
Useful resources
Request your free copy of the 2024 Building Code Compendium
OBC Transition Rules & Application for Permit - EABO graphic of transition timeline