Date: Mar 28 | Filed in Draft ordinance review | No comments yet.
We received the following comments from FEMA. The Consulting team has recommended to the County the changes noted in the document referenced in this post. The comments received were as follows:
- The definition of “base flood elevation” references NGVD 29 as the vertical datum defining flood elevations, and this is the datum used in the currently effective 2004 FIRMs and FIS, but elsewhere (Section 15-33), the ordinance directs the use of NAVD 88 in the context of directing accuracy standards for field measurement and documentation purposes, including for floodplain management. This raises three questions: (1) For efficient review of documents and to prevent mistakes, should surveyors and engineers working on projects in DuPage County indicate elevations in relation to both datums, or note the conversion factor that applies at the site location; (2) Where would the County prefer that they obtain a conversion factor (VERTCON?) since the current FIS does not address datum conversion; and looking to the future, (3) Will the revised DuPage Countywide FIRMs and FIS that are being prepared right now use NAVD 88—and in the future how will the ordinance address datum conversion, to prevent mistakes when comparing developments as-built, permit documentation, and maps from before and after the effective date of the new maps.
- I previously recommended that the term “basement,” which is included in the definition of “lowest floor,” be defined, as “any area of a building having its floor below grade on all sides”. If the term is not defined, it becomes unclear whether a crawlspace with a floor a few inches, or a few feet, below grade is required to be elevated to the flood protection elevation. If the floor of any area of a building is below grade on all sides it is a basement and it is the lowest floor for floodplain management purposes AND for flood insurance purposes unless it meets the crawlspace construction technical bulletin standards (FEMA Technical Bulletin 11). This may be counterintuitive to many people, that an inaccessible crawlspace could be considered a basement, or that a retention area used to meet compensatory storage requirements located beneath an otherwise elevated building might be considered a basement and therefore the lowest floor. From the floodplain management perspective it can lead to violations, and from the insurance perspective it can lead to some very expensive insurance premiums.
- The term “substantial improvement” is included in the definitions section twice, with minor differences between the two versions.