Floor Level Survey in San Francisco, CA

San Francisco splits cleanly between ground that moves and ground that does not. The bedrock and dense-sand neighborhoods on the hills are comparatively stable; the made ground is not. South of Market, Mission Bay, the Financial District waterfront, and the Marina sit on artificial fill over soft young bay mud, the same material that produced the concentrated damage in 1906 and again in the Marina in 1989, and that consolidates for decades under any load placed on it. The city’s own maps of liquefaction susceptibility track those fill areas closely. Settlement here is ordinary rather than exotic, which is why so many San Francisco structural reports end with an instruction to obtain a floor level survey and send it to the engineer.

The other local factor is that this city has a real vertical datum and expects it to be used. Public Works’ County Surveyor established CCSF-VD13 as the city vertical datum, a direct realization of NAVD88, and specifically prohibits converting old City Datum benchmarks by adding a constant. That matters for floor level work more than it might sound: a floor level survey on an arbitrary reference cannot be compared to the next one, to the building next door, or to a civil engineer’s site grades. We tie floor elevations to published benchmarks and deliver on VD13 or NAVD88, or on a project datum if the engineer specifies one, so a second epoch and a neighboring structure both land in the same frame.

Practically, most of what we measure here is soft-story and mixed-use buildings in the retrofit program, SoMa and Mission Bay residential towers and podiums, flats and Edwardians where a rear addition or a garage cut changed how the building carries load, and HOA buildings where a board needs an independent number set. We perform no foundation repair and bid none, so there is nothing in the result for us. The same visit can also capture the building itself — see our San Francisco as-built surveys — and for repeat measurement our deformation monitoring.