Seismic Retrofits in Multi-Residential Buildings
Canadian Property Management | August 2023
Leon Plett, P.Eng., MIStructE, Struct.Eng., LEED® AP | Managing Principal
Risks and opportunities in 2023 and beyond
Seismic activity is a natural occurrence that happens throughout the world. Defined as the sudden movement of the earth’s crust caused by the release of stress accumulated along geologic faults or by volcanic activity, severe earthquakes don’t happen very often, but when they do the results can be catastrophic. From triggering tsunamis to leveling buildings, the worst earthquakes in history have led to death tolls in the thousands, making them among the worst natural disasters known to civilization.
So, what does this mean for Canadian building owners? According to Leon Plett, Managing Principal at RJC Engineers, it’s a complicated issue with different rules and levels of urgency depending on where you live. While some regions in Canada are at higher risk of experiencing ground motions capable of structural damage—namely, along the east and west coasts of the country—no area is completely immune to the threat. As such, local governments have been calling on building owners for years to invest in upgrades to make their buildings more resistant to ground motion and soil failure due to earthquakes and tremors.
Here in BC, we have a significant stock of 1960s and 70s, four-storey, wood-frame buildings, most of which was constructed without an engineer on board,” Plett says. “Many of these
have soft storeys, undersized beams, and no defined seismic system. They were not built to withstand excessive ground shaking.”
That said, there’s still no requirement to improve the safety of an existing building against a seismic hazard. Only new building designs or buildings undergoing a significant change in use or renovation must upgrade for seismic resilience in accordance with the local municipality’s guidelines.
While the cost of a typical seismic upgrade is estimated to be less than $20,000 per unit for low-rise, wood framing buildings, the real deterrent for multi-residential building owners is the loss of income over the construction period, which Plett estimates can take six months to a year-and-a-half to complete.
“Upgrading a wood-frame building for seismic resilience involves strengthening the shear walls and the foundations, and a few other key areas,” he explains. “There’s a lot of plywood and nails and steel hardware needed but it’s relatively straightforward. We might have to put new anchors from the walls into the foundations to resist uplift, strengthen the walls with plywood sheathing, and improve the floor and roof diaphragms, which distribute those forces to the walls.”