kane county stormwater technical guidance manual - Kane County, IL

nonresidential), the flood insurance rates and premiums will be significantly
higher. In addition, the Certified Community can pursue legal action. For
substantially damaged structures which have their lowest floors, including
basements, several feet or more below the BFE, the annual premium cost
increase to thousands of dollars. The guidance provided here on substantial
improvement in is contained in Answers to Questions About Substantially
Damaged Buildings (Federal Emergency Management Agency, FEMA – 213,
May 1991).
Fill Placed to Elevate a Residential Structure must have the top of the fill and
lowest floor, including basement, at or above the FPE. A buffer of fill above
the FPE is required for a continuous distance of ten feet out from the building
to reduce the potential damages associated with hydrostatic forces on the
building. The top of the fill for an attached garage must be 0.5 foot above the
BFE. The fill shall not settle below the BFE for a residential structure and not
below 0.5 foot above the BFE for an attached garage.
The applicant will need to provide the Administrator with evidence that fill
placed to elevate a residential building is protected against erosion and
settlement below the FPE. It is strongly recommended that fill be placed in
accordance with the FEMA criteria for development. § 65.6 (a)(6) of the NFIP
regulations reads as follows:
(i) Fill must be compacted to 95 percent of the maximum density
obtainable with the Standard Proctor Test method used by the
American Society for Testing and Materials (ASTM Standard D-
698).
(ii) Fill slopes for granular materials are not steeper than one
vertical on one-and-one-half horizontal unless substantiating
data justifying steeper slopes is submitted.
(iii) Adequate protection is provided for fill slopes exposed to flood
waters with expected velocities during the occurrence of the
base flood of five feet per second or less by covering them with
grass, vines, weeds, or similar vegetation undergrowth.
(iv) Adequate protection is provided for fill slopes exposed to flood
waters with velocities during the occurrence of the base flood of
greater than five feet per second by armoring them with stone or
rock slope protection.”
Because the flood carrying capacity of the regulatory floodplain must be
maintained, fill placed in the regulatory floodplain must be shown to not
singularly or cumulatively create a damaging increase in flood heights or
velocities, or impair the natural hydrologic functions of the floodplain or
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