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Our house is a four-square style over a concrete foundation, built in 1918. We're in the Pacific-Northwest, so we're thinking about hiring someone to bolt the house to the foundation in case of the Cascadia Subduction earthquake that everyone's been talking about.

We just had a contractor come in and say he could do the job with epoxy. I found that pretty hard to believe; how could he apply epoxy between the wood and the concrete when they're sandwiched together? Can I trust epoxy to hold onto the house and concrete, and not just peel the outer layers of wood?

That got me thinking that I don't know anything about seismic retrofitting. So my question is, what should I look for when choosing a bolting approach? I have what they call "cripple walls", so does that require special treatment? How far apart should the braces be positioned? Here's an image of my basement: enter image description here

I saw this video explaining at 7:08 that you could use very thick plywood and special metal braces to drill and attach the house structure to the concrete. Is this the best approach? I thought the bolts would point down, not horizontal on the face of the concrete, see screenshot below:

Screenshot of video

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    Do not think you want solid fix, but one that has some movement that keeps the house together. You want a seismic retrofitting contractor, that should be able to show license/certifications to do the job. They say if it lets go it should be above 9+, it just might be cheaper to build a new house than to retrofit a house that old, but you are betting it happens sooner than later. – crip659 Feb 17 '23 at 00:20
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    Epoxy is often used to anchor bolts drilled into concrete, so you should have asked a few questions of the "epoxy" contractor to determine how they intended to use it. Works well if it's not substandard epoxy, like this: https://en.wikipedia.org/wiki/Big_Dig_ceiling_collapse – Ecnerwal Feb 17 '23 at 00:49
  • **VERTICAL BOLTS** – Ruskes Feb 17 '23 at 04:51
  • The pictured plates are like a “Simpson URFP-SDS3”, which has horizontal bolts and holds the plate to the foundation. Your cripple wall might need plywood to provide shear strength. Find a contractor with seismic retrofit experience and they should be able to explain all of their recommendations. – Aloysius Defenestrate Feb 17 '23 at 12:44
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    This is an overly broad question, basically, "how do I do a seismic retrofit of my house". The answer to that fills many books and papers. Please pick _one_ single aspect that you need specific details on. If necessary, you can then ask follow up questions to get more details on the other parts. – FreeMan Feb 17 '23 at 15:18
  • In general, though, you do _not_ want a completely rigid connection. The goal is to allow things to move _without_ moving too much and falling apart, thus the curved metal bracket in the last image. – FreeMan Feb 17 '23 at 15:21

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