Seismic Retrofit Evaluation in Southeast Portland
The bungalow belt is the most retrofittable housing stock in the city, and the reason is that almost all of it shares the same two deficiencies. The house is not bolted to its foundation, and the short stud wall between the foundation and the first floor — the cripple wall — has no bracing in it.
Those two things produce one failure mode. In a strong earthquake the foundation moves with the ground, the house above wants to keep still, and with nothing connecting them and nothing resisting racking in that short wall, the house slides off or the cripple wall folds over. It is the single most common way wood-frame houses are lost in a major event, and it is also among the cheapest structural problems in existence to fix.
The evaluation is not really about whether those deficiencies exist — in a pre-1974 Southeast bungalow they almost certainly do. It is about whether the foundation is in a condition that will hold the retrofit, because bolting a house to a foundation that cannot take an anchor accomplishes nothing.
What We Look At Here
- Presence, spacing and condition of anchor bolts connecting sill plate to foundation
- Cripple wall height and whether any bracing or sheathing exists
- Foundation concrete quality and whether it can hold a modern anchor
- Sill plate condition, since rot removes the very member the bolts pass through
- Post and girder bearing in the crawl space, and connections at each end
- Whether the house has been partly retrofitted before, and to what standard
More on the service itself: Seismic Retrofit Evaluation. More on the area: Southeast Portland.
Questions
Frequently Asked Questions
Does my Southeast Portland bungalow need a seismic retrofit?
If it was built before about 1974 and has not been retrofitted, it is very likely unbolted with an unbraced cripple wall. The more useful question is usually whether the foundation is sound enough to anchor to, which is what the evaluation establishes.
Can a retrofit be done if the sill plate is rotten?
Not until the rot is dealt with. Anchor bolts clamp the sill to the foundation, so a decayed sill gives them nothing to hold. Sill replacement usually has to happen first or as part of the same job.