How to install seismic anchor bolts

How to install seismic anchor bolts

If you ever open up your walls like we did, one of the things to consider is adding/upgrading seismic anchor bolts – these basically serve to secure your home to the slab that it sits on in case the ground moves laterally during an earthquake.

I ended up installing 5/8″ anchor bolts roughly every other bay throughout all exterior walls. I left the existing ones in place and just upgraded their washers with 2″ square ones because I’ve heard that the original, smaller washers, can pull through the mud sill (2×4) when under heavy stress. Be sure to spray a lot of WD-40 on the existing bolts and let it sit for a week before attempting to remove the nuts. They were like new after one week – that stuff is amazing. Pics from left to right are: new bolt, old after upgrade, old before upgrade (original).

Here are the steps I took:

1. Drill a 5/8″ hole through the mud sill and into the foundation with a hammer drill and masonry drill bit to a measured depth by putting tape on the drill bit at the depth you want to achieve. You want the bolt to hit the bottom of the hole and still have enough thread for the washer and nut.

2. I used wedge anchors from home depot that you just hammer into the hole and when it hits the bottom of the hole the base expands and locks it into place. Note: be sure to put the washer and nut on before you start hammering since you might mess up the threads making it difficult to thread the nut on after hammering..

3. Tighten nut.

Some people prefer the type of anchor bolt that you epoxy into place, but I went the simpler route.

I was lucky enough to get to borrow our plumbers’ giant bosch hammer drill which made this pretty easy. Be sure you aren’t going to drill through any original plumbing. We abandoned ours so I didn’t have to worry about this.

I found a website that has a lot of useful information about this here:


2 thoughts on “How to install seismic anchor bolts

  1. I am having this done now. I don’t think you need to worry about the radiant that close to the end of the foundation. At least I hope not…

    1. I think you’re right.. I don’t recall hitting any pipes, and it wouldn’t make sense to be heating up the floor under the walls.. Were there any plumbing pipes run under the walls though? I can’t recall, but seems like there might have been. We replaced all the plumbing and electrical so it wasn’t an issue.

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