To foundation bolt or not to foundation bolt

When you inspect the foundation of an older apartment building in LA, probably 7 out of 10 times, your foundation inspector is going to tell you that the foundation isn’t bolted and that you should bolt it after you buy it. Should you?

To answer the question, you first need to understand how these older foundations work. Imagine a low, concrete wall running around the perimeter of the building. Then, imagine imagine a strip of wood lying flat atop the wall (this is called the mud sill), with other pieces of wood rising straight up from the flat ones every 16″. The wood I’ve described is the framing that comprises the building.

Here’s a picture from a building I recently inspected:

You can see that there’s nothing holding the flat wood (called the mud sill) on top of the the concrete wall besides gravity. This is the case for most older buildings.

Can you imagine what can happen to a building with a foundation like this in an earthquake? If there’s enough shaking in the right direction, the framing (the wood) can jump right off the concrete wall. That’s potentially disastrous, because the framing will be stressed in all kinds of ways its not designed to be stressed and the structure will rupture.

Foundation bolting is pretty much exactly what it sounds like: A licensed foundation contractor comes in and bolts steel plates to both the concrete and the framing, keeping them from separating. If you go for cripple wall reinforcement, then the contractor also connects plywood to the vertical lumber rising out of the mud sill to stop it from moving side-to-side in an earthquake.

So, should you pay to have your foundation bolted and reinforced? Well, an earthquake is pretty much the only thing that can totally screw up an investment in an apartment building, because you’re almost definitely not going to have earthquake insurance (because it’s too expensive). And foundation reinforcement is reasonably cheap (probably $10-15k, depending on the size of the building).

So, here’s my advice (and remember, I’m not an engineer or contractor or anything, just someone who has had to make this decision about 15 times recently):

  • Always bolt 2+ story buildings (it’s a lot harder to fix these if the framing jumps off the foundation AND people are much more likely to be hurt if it does)
  • Err on the side of bolting single story buildings unless the cost of doing so causes you not to be able to do the deal, in which case do the deal and worry about the bolting later