First question would be how did they put in fairly deep piers (by residential standards) without demolishing the house?

I'm not sure. Under the general requirements portion, they put this...

Referring to enclosed Plate D, it is noted that the recommended underpinning encompasses only the main structure where the excessive differential settlements have occurred. You may want to consider extending the underpinning around the entire structure at this time, to provide additional rigidity to the front room.

I do not have enclosed Plate D, unfortunately, or any diagrams from the original estimate. So I dunno if the underpinning encompasses both alternate solutions (Reinforced Concrete Drilled Piers vs. Pipe Piles) but I think it refers to that.

So in that case they might not have had to move the house to do the piers, but ...

I hope they haven't just simply locally elevated the house at its supports, dug a slightly deeper trench and called it day. If there's no definitive proof that the piers have been done, it probably hasn't been done.

I think it hasn't been done. Two things lead me to believe this.

• For the work in '95 we have: permit, contract, and receipt of final payment. We only have a contract signed on the '88 work which was to include the pier, and that contract was for payment upon work done. There's no receipt, there's no permit from the city. Clearly we'd have to go to the city and see if there was a permit, but even that doesn't mean they did it.
• If in '88 they really did the work they said they would do re-leveling the house and installing those piers, would ANOTHER company come back in '95 to re-level, again, and replace the wooden underpinning with adjustable steel ones?

I think they balked at the hefty price in '88 (this was a woman who would have been in her late 60's, early 70's at that time in a house worth much less at the time) and eventually had to do something in '95 and found someone who would do the re-leveling and re-underpinning without requiring them to do the piers.

The house doesn't seem elevated in the FRONT, at all, where it meets the earth at the street... and in fact, in none of the work that I can see (either the contract in '88 that I don't think was fulfilled, now, or the work in '95 that WAS certainly done) is the front of the house referenced, it's only the back like... 25-33%.

From the report...

The contours on Place C indicate that a maximum differential settlement of 3.8 inches has occurred under the rear side of the house. A differential settlement of approximately 0.8 inches was recorded in the front living area.

As with all things underground, it's very, very hard to know for sure, the only thing you can really go on is past experience (and bore logs of course).

They actually do have bore logs in the '88 estimate. That's also where I think they drew the conclusion that the groundwater was pretty low.

They noted that:

The excess moisture problem noted in the rear bedroom does not appear to be directly related to the groundwater, which was encountered below depths of 9 to 18 feet. However, it is possible that the problem may be related to a capillary rise of moisture in the fine-grained subsoils...

I would be particularly worried if the house was of brittle construction (ie; masonry), if it's of brittle construction and has been around since the 50's, even a minor earthquake could be catastrophic.

Yeah, I'm not sure how to check that. Based on how the house looks I don't think it is... but I guess a structural engineer could tell us, most likely.

(This house is about 10 miles from the side of the Bay Bridge that collapsed in the World Series earthquake of 1989.)