NAVD88 or NGVD29? Confusion of Vertical Datums

VERTCON Height Differences between NAVD88 & NGVD29

As we perform our survey work and provide elevation certificates, we find that there is quite a confusion as to what the elevation datum the public is referencing. NGVD29 or NAVD88? The latest adopted vertical datum is NAVD88 for local and federal governments. As the switch from old plans to new, the conversion can be wrongly utilized for construction. This confusion can end up being very costly by incorrect construction or insurance premiums by the change or difference in the two datums elevation. As with South Florida, for example, Tampa Bay area the difference from NGVD29 to NAVD88 is lower by about 0.8 to 0.9 feet, while in Fort Myers/Naples the change is 1.4 to 1.6 feet lower. See the attached image for the height differences in centimeters.

FEMA Flood Insurance Rate Maps have been slowly updating from NGVD29 to NAVD88, so when the homes are constructed or are older, these homeowners typically do not know which datum they are referencing and thus the confusion. For a complete description via the web, click on the links below.

NAVD88 Wikipedia
NGVD29 Wikipedia
Conversion of datums VERTCON