Although earthquakes are rare in Oregon and Washington, the Cascadia Subduction Zone and numerous faults pose a very real risk of significant seismic damage. Homes built before 1970 are at the greatest risk, often requiring retrofits even to become eligible for earthquake insurance. A mix of upgrades, tailored to your home, can greatly reduce financial and safety risks to your home and family.
What You Should Know
The Pacific Northwest is vulnerable to movement of the Earth’s crust along the offshore Cascadia Subduction Zone, where two plates meet, as well as from numerous faults that run under populated regions including the Portland, Tacoma and Seattle metropolitan areas. Long-term indicators show a pattern of major quakes about every 500 years. A devastating earthquake occurred 300 years ago and scientists say another could occur at any time.
Because earthquakes occur less frequently here than in more active areas such as California, structures are less likely to be retrofitted and occupants are generally less prepared, which increases occupant risk. Understanding the risks and taking action can help you protect your home and family.
Risk factors include the age and condition of the structure, construction materials, configuration of the walls, basement, crawlspace or slab, slope of the lot and the number of stories. Upgrades will usually fall into one of two categories:
- Prescriptive path: For suitable homes, this path includes upgrades such as braced walls, sheathing, and bolting the home to the foundation.
- Engineered path: For homes ineligible for the prescriptive path, a licensed engineer will design a solution.
Note that both paths usually require a building permit. Upon successful inspection, the home may become eligible for earthquake insurance.*
Cost and Lifetime Value
- Reduced risk to structure and occupants
- Earthquake insurance eligibility.*
Key Home Seismic Upgrades
Seismic retrofits vary in complexity and cost. Evaluation by a seismic professional will help you determine your level of risk, and what upgrades will provide the most effective protection.
- Foundation anchors: Connect the wall to the foundation; keep house in place. Vertical bolts are used where space allows. Foundation brackets with horizontal bolts are used where space does not permit vertical bolts
- Framing anchors: Attach rim joist to mud sills and floor joist to mud sills
- Water heater strapping: Prevents heater falling and causing water damage; can be emergency drinking water source
- Gas emergency shutoff valve: Reduces risk of fires
- Shear wall: New plywood added to basement wood frame “cripple” wall protects against side-to-side movement
- Improved masonry: Footers and basement walls made of concrete, brick or stone may need evaluation and reinforcement or replacement
- Post and beam reinforcement: Brackets add resistance to side-to-side motion
- Porch strengthening Adds new posts and beams inside historic box beams and hollow columns
- Chimney banding and bracing or removal: Reduces risk of chimney collapse, injury to occupants and damage to structure
Thinking of starting a seismic project? The first step is to schedule a phone consultation with a Community Energy Project Home Advisor.
*Consult your insurance provider for specific requirements.