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Seismic Retrofit
Seismic retrofits help reduce earthquake damage.
British Columbia Building Codes and Vancouver By-laws ensure any new builds or major renovations include seismic provisions. However, homes built prior to 1990 rarely have earthquake resistant features installed during construction. It’s wise for homeowners living in active seismic zones (such as Greater Vancouver), to retrofit homes to prevent damage and injury. The process improves your home’s ability to keep inhabitants safe during an earthquake, and homes habitable after a major disaster. Retrofitting can either prevent damage altogether, or drastically reduce repair costs after seismic events.
Many structures were built to withstand only the force of gravity—an up-and-down force. It turns out the most damaging component of earthquake force is the lateral movement (side-to-side). This means that the lateral stresses of earthquakes compromise structures even when they’re solidly built to resist typical non-seismic forces.
Houses built before 1990 often have some (or all) of the following weak points:
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The foundation isn’t anchored to the house.
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The wood-framed basement walls don’t offer enough support.
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The floor of the house doesn’t connect to the basement walls.
Basement Wall Bracing
Many structures are built on pony walls. Pony walls are short walls on a home’s foundation, that support the floor and exterior walls. Unbraced, these walls can shift in an earthquake, increasing the risk of injury to the occupants and severe damage to the home. Bracing these walls strengthens structures by increasing stability against shear forces, and typically reduces damage to homes.
Foundation Anchoring
Houses not bolted to their foundation may move during an earthquake. Homes that move off their foundation may also cause gas lines to rupture, which may lead to fires. We remedy this by drilling holes through the sill plate and installing anchor bolts to the foundation.
Floor Fastening
If the floor of the house isn’t attached to the top of the basement pony wall, the house can slide off the basement wall during an earthquake and subsequent aftershocks. Bracing the basement pony wall with plywood prevents collapse and secures the home to the foundation. We use shear force seismic transfer ties, which are brackets connecting the floor framing to the pony wall.
Utility Retrofitting
Water tank: seismic activity can overturn unbraced hot water tanks. Using straps, spacers, and screws, we can secure your hot water tank seismic to the wall framing. This means that if basic services become unavailable after an earthquake, you will also have an invaluable source of potable water.
Gas meter shutoff: in an earthquake, your home’s gas line may leak or rupture. To prevent this, an emergency earthquake gas shutoff valve will close the gas line to your home, reducing the risk of explosion or fire during and after earthquake.
Call Wallace Underpinning today to discuss options for your seismic retrofit.
