My elevations are off by about 90 feet

What's happening

Every elevation — on the map, in the contours, in the point cloud — reads roughly 90 ft below what the site actually is, and the legend may start near zero or go negative. Nothing is broken. The export is carrying GPS (ellipsoidal) heights, which are measured from a mathematical model of the earth that sits about 90 ft away from mean sea level across much of the United States. The numbers are answering a different question than the one your client is asking.

What to check

1. Compare one known point — a benchmark, or a road elevation on the plans — against what the map reports.
2. Confirm the error is consistent across the whole site. A roughly equal deficit everywhere is the signature of this problem.
3. If the error varies from point to point, stop: this is something else and this fix will not help.

How to fix it

1. Choose the correct vertical datum for the project so heights are converted to orthometric elevations.
2. The datum is set at upload, and can be corrected afterwards without re-uploading.

Avoiding it next time

Set the vertical datum when you create the project rather than after the fact. It is the single field on the form that most often decides whether the numbers are usable.