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El Certs, Zone A, and Contour Interpolation
I had a episode this week involving a realtor who didn’t want to wait for the county to determine the BFE in a Zone A (as the county is required to do). She actually contacted some neighbors and asked them for their elevation certificates, then asked me to use the BFE listed on their elevation certificates. I told her I could not do that since Zone A lots are evaluated on a case-by-case basis, and I have no idea how they came up with those BFEs. So she then contacted one of the surveyors involved with a neighbor’s elevation certificate, and he told her that he came up with the BFE himself by tracing contours from a USGS quad map onto the FIRM map, and assumed the nearest contour elevation (to the zone line) was intended to be the BFE. I told her I did not agree with that method and I would not do that. She got upset and said she was going to fire me (she wasn’t even the person that hired me) and have the other surveyor do it. But, she did back off that position. I kinda have the impression that the other surveyor bad-mouthed me because I was told by the realtor that this method is “common knowledge that any surveyor should know” and “every surveyor that works in this particular city know the BFE in that area is X”.
I researched this method on the FEMA website and found this:
Guide For Approximate Zone A Areas
Developing BFEs
Simplified Methods
Simplified methods may not be used by the community to complete
an Elevation Certificate used for flood insurance rating.
Communities must use the detailed methodologies described in
this section or other methods comparable to those in a Flood
Insurance Study for completing the Elevation Certificate. A
flood insurance policy for a structure for which a simplified
method is used may be rated without an elevation certificate.
However, the flood insurance rate may be higher than if the
structure is rated using an Elevation Certificate.Contour Interpolation
Contour interpolation involves superimposing approximate Zone A
boundaries onto a topographic map in order to estimate a BFE….http://www.fema.gov/library/viewRecord.do?id=2215
That link is a very interesting read for anyone who often gets requests for Zone A elevation certificates. My impression from reading through the “detailed method” is that to determine a BFE acceptable for elevation certificates, one would need sophisticated computer models and access to watershed and flood data that’s not readily available to the public. In other words, a surveyor should not be trying to determine Zone A BFE’s for flood insurance purposes. However, when this topic has come up on the old board, I recall a few surveyors recommending the contour interpolation method.
And the best part is, in the end, the county determined the BFE was 2′ different (lower) than the other surveyor’s. That caused this building to be rated as a +3′ instead of a +1′. I would think that I could have been liable for the difference between the two rates had I submitted an inaccurate BFE based on an unapproved method, and the buyer had paid the higher rate for several years. I wonder if I should return the favor and contact the neighbor and let them know they are probably overpaying for flood insurance … hmmmm.
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2 Replies
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If the other surveyor used that method, and that method was accepted and approved by FEMA as the BFE then the only difference would be that you decided to do the right thing by not accepting the other surveyors work. Although his work was approved by FEMA, the question remains was the county’s determination also accepted by FEMA. I’ll assume that based on your post it was.
Very interesting post.
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This has been debated for years.
We have done the contour interpolation many times. We were contacted only once by a FEMA rep. All he wanted to know was what assumptions we had made. Obviously, assuming anything has it dangers, but, sometimes that’s about all that is left short of a fullblown analysis that is based on way too many assumptions in the first place.
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