What vertical datum should we use for a new project?

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Engineers sometimes give us old benchmarks on different datums. How do we pick?

Asked October 25, 2026

AI answer · not yet verified by a surveyor

Use the datum the project requires, and state it clearly [1].

  • Default for new work: NAVD 88, until NSRS modernization rolls out, unless the client, agency or municipality specifies otherwise.
  • Flood work: use the datum of the FEMA flood map. Many newer maps use NAVD 88, while older ones may use NGVD 29 [2].
  • Local systems: some municipalities or campuses have their own datums. Document any conversion.

Avoid problems:

  • Confirm the benchmark's datum and its current published height.
  • Check into at least two benchmarks if you can.
  • Note the datum and benchmark on every drawing.
  • Convert carefully, using official tools such as NGS VERTCON or current NGS tools where appropriate, and document the method.

Most "elevation disagreements" between surveys trace back to different datums.

Sources

  1. When Survey Elevations Disagree, Check the Datum Before Changing Grades
  2. What is a flood certification? A Comprehensive Guide.

General information only. Answers here are not a survey or legal advice, and no one here can tell you where your boundary is. For your property, hire a licensed land surveyor in your state; for legal questions, a real-estate attorney.

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