How Home Seismic Retrofits Work

Home seismic retrofits target parts of the home that are most likely to fail, and add additional materials and fasteners for greater strength. Every older home is different, and upgrades typically fall into two categories and price points.

1. Prescriptive path:

For suitable homes with strong foundations and meeting other criteria, this path includes upgrades such as braced walls, sheathing, and bolting the home to the foundation.

2. Engineered path:

For homes with weak foundations, on steep slopes, or otherwise are 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.*

Components of a seismic retrofit

1. Foundation anchors

Connect the wall to the foundation; keep house in place. Vertical bolts aʳe used where space allows

Foundation plates with horizontal bolts are used where space does not permit vertical bolts

2. Framing anchors

Attach rim joist to mud sills and floor joist to mud sills

3. Water heater

Strapping prevents heater falling and causing water damage; can be emergency drinking water source

4. Gas valve

Automatic emergency shutoff valve reduces risk of fires

5. Shear wall

New plywood added to basement wood frame “cripple wall” protects against side-to-side movement

6. Masonry

Footers and basement walls made of concrete, brick or stone may need evaluation and reinforcement or replacement

7. Post and beam

Reinforcement brackets add resistance to side-to-side motion

8. Porch

Strengthening adds new posts and beams inside historic box beams and hollow columns

9. Chimney

Bracing or removal reduces risk of chimney collapse, injury to occupants and damage to structure

Two ways to bolt down the house

1. Interior option – for unfinished basements and crawlspaces

Two ways to bolt the house to the foundation (seismic retrofit)

Foundation plate: In crawlspaces and unfinished basements, installation of plates like this one connect the wood structure to the foundation.

Framing angles and other hardware: Strengthen connections between frame components.

2. Exterior option – minimizes disruption to finished basements

Seismic retrofit - bolt home to foundation with exterior anchors

Exterior plate and bracket retrofit in progress. This is a good option with finished basements because it does not require removal and replacement of drywall.

Exterior plate after completion and painting. The plates extend only a few inches below siding and are very inconspicuous.

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