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For the geologists in the house: I live in a new construction home with a post-tensioned slab foundation about 4 miles from the Hayward fault -- in a vertical

For the geologists in the house: I live in a new construction home with a post-tensioned slab foundation about 4 miles from the Hayward fault -- in a vertical line straight down. How worried should I be?

Waterluvian 9y ago
Probably a better question for the builders and civil engineers.
- jraines 9y ago
  Good point. The builders gave all assurances, but they're also the seller, so ¯\_(ツ)_/¯
wiredfool 9y ago
Roughly, I'd say your biggest danger is falling objects, like books, and fire. Building codes for new construction do most of the obvious now, the walls are tied to the foundation, there are shear panels. 5 to 15 stories is the worst height range, but shorter buildings can be bad if they're very asymmetric, like one with a parking under a two story appt, with one shear wall and poles for gravity support. otoh, in a big enough earthquake, anything will be damaged.
- shostack 9y ago
  What year did the "walls are tied to the foundation" bit become code? If I'm in a 50+ year old house, what are the main things to check for? I've heard that there is shockingly little consistency with retrofit companies and the work they do, and that the inspections aren't really great for those things, but I know next to nothing about making sure one's home is properly fitted.
  - wiredfool 9y ago
    It was well known when I did civil engineering in the mid 90s, I want to say that it was post Northridge that it started to bubble through the code. 50 years is probably pre-foundation tiedown. Current construction is going to have long sheet metal straps or j bolts into the foundation, I'm not sure what a retrofit will have. An easy thing to check is the hot water tank. If it's not well strapped to studs, then I can't imagine anything else has been done. If it has, then at least you know that has been done, it it doesn't really tell you anything else. I know when I was selling my house in Wa, that was one of the things the inspector looked for, so it's highly probable that it's been done, as its quick and easy. Inspections are the only way to know for sure, but it can be invasive to get into the walls enough to see.
    - shostack 9y ago
      Thanks for the info. Water heater has two metal straps to the studs and is on a raised platform, so that's taken care of. The foundation is slightly raised on post and pier with no sheering panels or bolts in the posts that I can see, but the exterior walls look like they may be bolted to concrete the foundation perimeter. Any tips on making sure a retrofit company is legit? My biggest concern is I'd heard that the inspections for getting a retrofit aren't super consistent or thorough, which is a huge concern.

Waterluvian 9y ago

Probably a better question for the builders and civil engineers.

jraines 9y ago
Good point. The builders gave all assurances, but they're also the seller, so ¯\_(ツ)_/¯

wiredfool 9y ago

Roughly, I'd say your biggest danger is falling objects, like books, and fire. Building codes for new construction do most of the obvious now, the walls are tied to the foundation, there are shear panels. 5 to 15 stories is the worst height range, but shorter buildings can be bad if they're very asymmetric, like one with a parking under a two story appt, with one shear wall and poles for gravity support. otoh, in a big enough earthquake, anything will be damaged.

shostack 9y ago
What year did the "walls are tied to the foundation" bit become code? If I'm in a 50+ year old house, what are the main things to check for? I've heard that there is shockingly little consistency with retrofit companies and the work they do, and that the inspections aren't really great for those things, but I know next to nothing about making sure one's home is properly fitted.
- wiredfool 9y ago
  It was well known when I did civil engineering in the mid 90s, I want to say that it was post Northridge that it started to bubble through the code. 50 years is probably pre-foundation tiedown. Current construction is going to have long sheet metal straps or j bolts into the foundation, I'm not sure what a retrofit will have. An easy thing to check is the hot water tank. If it's not well strapped to studs, then I can't imagine anything else has been done. If it has, then at least you know that has been done, it it doesn't really tell you anything else. I know when I was selling my house in Wa, that was one of the things the inspector looked for, so it's highly probable that it's been done, as its quick and easy. Inspections are the only way to know for sure, but it can be invasive to get into the walls enough to see.
  - shostack 9y ago
    Thanks for the info. Water heater has two metal straps to the studs and is on a raised platform, so that's taken care of. The foundation is slightly raised on post and pier with no sheering panels or bolts in the posts that I can see, but the exterior walls look like they may be bolted to concrete the foundation perimeter. Any tips on making sure a retrofit company is legit? My biggest concern is I'd heard that the inspections for getting a retrofit aren't super consistent or thorough, which is a huge concern.