Seismic Retrofit in Seattle, Bellevue & the Eastside
A seismic retrofit bolts a house to its foundation, braces weak crawlspace walls and adds hold-downs so the structure stays on its foundation in an earthquake. It matters most for wood houses built before the 1980s, especially older Seattle homes with cripple walls. A basic engineered retrofit typically costs $8,000–$20,000; garage and soft-story upgrades run $25,000–$80,000.
Reviewed by Daniel R. Whitcomb, PE · WA PE 48217
Why do older Puget Sound houses slide off their foundations?
The Puget Sound region sits above several earthquake sources: the Cascadia subduction zone offshore, deep earthquakes within the subducting plate like those felt across the region in the past, and shallow crustal faults including the Seattle Fault, which runs east–west beneath Seattle, Mercer Island and Bellevue. The Washington Department of Natural Resources maps these hazards.
In older wood houses the weak point is usually at the bottom. Many houses built before modern code were set on the foundation with few or no anchor bolts, and many Seattle houses stand on short wood "cripple walls" between the foundation and the first floor that have no bracing. In strong shaking, the house can slide off the foundation or the cripple walls can fold over. Both failures are well understood, and both are fixed at relatively low cost compared with the damage they prevent.
What does an ECD seismic retrofit include?
- An engineering evaluation of the foundation, sill, cripple walls, chimney and any living space over a garage.
- Retrofit drawings and calculations, or use of the jurisdiction's prescriptive plan where the house qualifies.
- Foundation anchor bolts or plates connecting the sill to the concrete.
- Plywood bracing of cripple walls with the required nailing and venting.
- Connectors tying the floor framing to the sill and braced walls.
- Permit, inspections and an engineer's completion letter for your records and insurer.
Additional scopes when found
Soft-story and garage upgrades with engineered shear walls or steel frames, chimney bracing or removal above the roofline, and foundation repair where the concrete is too deteriorated to anchor into. These are evaluated at the first visit and priced separately.
What are the steps in a retrofit?
- Engineering evaluationOne visit, 1–2 hours
Crawlspace or basement inspected; concrete quality and framing checked.
- Retrofit design1–3 weeks
Engineered plan or prescriptive plan prepared for your house.
- Permit1–6 weeks
Simple retrofits often move quickly through review.
- Installation3–10 days
Bolting, bracing and connectors installed from the crawlspace or basement.
- Inspection and completion letter1 week
City inspection, engineer's observation and documentation.
How much does a seismic retrofit cost?
| Scope | Typical cost | On-site time |
|---|---|---|
| Bolting only, accessible crawlspace, no cripple walls | $5,000–$10,000 | 2–4 days |
| Bolting and cripple wall bracing, engineered plan | $8,000–$20,000 | 4–8 days |
| Retrofit of a finished basement (walls opened and restored) | $15,000–$35,000 | 1–3 weeks |
| Chimney bracing or removal above roof | $3,000–$12,000 | 2–5 days |
| Living space over garage, soft-story upgrade | $25,000–$80,000 | 2–5 weeks |
What do Seattle and Eastside cities require for retrofits?
Retrofits are voluntary for single-family homes in Washington, but the work needs a building permit. The Seattle Department of Construction and Inspections accepts a prescriptive retrofit plan for houses that meet its limits, and engineered plans for the rest. Eastside cities review retrofits as structural permits through MyBuildingPermit.com. Nationally, FEMA publishes guidance on assessing and retrofitting one- and two-family houses that engineers use as a reference. For the full picture on older houses, read our guide to seismic retrofit for older Seattle homes.
A retrofit we completed
PROJECT · SEATTLE · WALLINGFORDCraftsman bungalow bolted and braced on 30-inch cripple wallsEngineered plan, foundation plates, plywood bracing and a braced chimney, completed in seven working days.Retrofit questions
Seismic retrofit FAQ
How much does a seismic retrofit cost in Seattle?
A typical Seattle retrofit with foundation bolting and cripple wall bracing costs $8,000 to $20,000 including engineering and permit. Bolting alone in an open crawlspace can be $5,000 to $10,000. Finished basements, where walls must be opened and restored, run $15,000 to $35,000, and houses with living space over a garage can need $25,000 to $80,000 of engineered work.
Does my house need a seismic retrofit?
If it is a wood-framed house built before the 1980s and you cannot see anchor bolts or plates connecting the wood sill to the concrete foundation, it likely benefits from one. Cripple walls without plywood, a brick chimney and rooms over a garage add to the need. Newer houses were generally built with anchorage and bracing and rarely need the same work.
Can I use a prescriptive plan instead of an engineer?
For simple houses that meet the plan's limits, yes. Seattle's prescriptive retrofit plan covers many one- and two-story houses on level lots with short cripple walls. Hillside houses, tall cripple walls, poor concrete, finished basements and rooms over garages fall outside those limits and need an engineered design. Our engineer tells you which path fits at the first visit.
Will a retrofit lower my earthquake insurance premium?
Some insurers offer lower premiums or deductibles for retrofitted houses, and some require documentation of the work before writing a policy. Ask your carrier what it requires. We provide the permit record, photos and an engineer's completion letter, which is the documentation insurers typically request.
What should be done about a brick chimney?
Unreinforced brick chimneys often break at the roofline in strong shaking and can fall through the roof or onto a walkway. Options are bracing the chimney to the roof framing, removing it above the roofline and capping it, or replacing it with a lightweight framed chase and metal flue. The engineer recommends one based on the chimney's height and condition.
Free estimate · Bellevue office
Talk to the engineer before you commit to a plan
A site visit, a scope conversation and a written budget range, at no cost.