Search results
Conversion between NAVD 88 and the commonly used NGVD 29 varies spatially; however, over most of the study area the following conversion can be used: NGVD 29 = NAVD 88 –3.6 feet. This conversion generally is accurate within about ± 0.5 feet for 95 percent of the study area.
NFIP Vertical Datum p. 7 Conversion Instructions. In the first example, the countywide conversion factor is -0.609. The elevation in NAVD 88 would be: 54.2 + -0.609 = 53.591 or 53.6 ft. Remember, if you add a negative number to the existing elevation, the resulting elevation will be a lower number.
- 885KB
- 12
This document contains the fol lowing information about conversion from the NGVD29 to NAVD88: • General information about the two vertical datums most commonly used by FEMA for referencing 1% annual chance flood elevation information in Flood Insurance Rate Map
- 335KB
- 15
document contains the following information about conversion from NGVD 29 to NAVD 88: General information about the two vertical datums most commonly used by FEMA for referencing 1-percent-annual-chance flood elevation information in Flood Insurance Rate Map (FIRM) databases, on FIRMs, and in Flood Insurance Studies (FISs).
NAVD 1988 is the newer elevation datum. An easy way to convert BFE data is through the National Geodetic Survey (NGS) online tool known as VERTCON. Select this link to view and use the VERTCON site. You can also contact the appropriate floodplain administrator for guidance.
Conversion Factor Example A building finished floor elevation is shown on an existing elevation certificate as 10.0’ NGVD. The equivalent NAVD 88 elevation can be obtained using the FEMA-approved average conversion factor in the following formula: NAVD 88 = NGVD 29 + conversion factor NAVD 88 = 10.0’ NGVD + (-1.51) NAVD 88 = 8.49
How Does One Convert From NGVD to NAVD? The conversion from one datum to another is a simple concept: define a conversion factor and apply it. The direction of the conversion around Cape Cod is negative as sea level has risen here. Therefore, the factor is subtracted from an NGVD 29 elevation to become an NAVD 88 elevation.
