Washington Model Flood Damage Prevention Ordinance Appendix A

Appendix A: Communities with Shallow Flooding Identified as an AO Zones on Flood Insurance Rate Maps (FIRM)

5.5 Standards for Shallow Flooding Areas (AO Zones) (44 CFR 60.3(c)(7)(8))

Shallow flooding areas appear on FIRMs as AO zones with depth designations. The base flood depths in these zones range from 1 to 3 feet above ground where a clearly defined channel does not exist, or where the path of flooding is unpredictable and where velocity flow may be evident. Such flooding is usually characterized as sheet flow. In these areas, the following provisions apply:

1) New construction and substantial improvements of residential structures and manufactured homes within AO zones shall have the lowest floor (including basement) elevated above the highest adjacent grade to the structure, one foot or more above* the depth number specified in feet on the community’s FIRM (at least two feet above the highest adjacent grade to the structure if no depth number is specified).

* Minimum standards require the lowest floor to be elevated “to or above” the BFE; however, adding an additional foot of freeboard increases safety and can significantly reduce insurance premiums. Adopting additional freeboard is strongly encouraged by FEMA. This note applies throughout Appendix A.

2) New construction and substantial improvements of nonresidential structures within AO zones shall either:

i) Have the lowest floor (including basement) elevated above the highest adjacent grade of the building site, one foot or more above the depth number specified on the FIRM (at least two feet if no depth number is specified) * Recorded on a current elevation certificate (FF 81-31) with section E completed; or

ii) Together with attendant utility and sanitary facilities, be completely flood proofed to or above that level so that any space below that level is watertight with walls substantially impermeable to the passage of water and with structural components having the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy. If this method is used, compliance shall be certified by a registered professional engineer or architect as in section 5.2-2(3).

3) Require adequate drainage paths around structures on slopes to guide floodwaters around and away from proposed structures.

4) Recreational vehicles placed on sites within AO Zones on the community’s FIRM are required to either:

i) Be on the site for fewer than 180 consecutive days, or

ii) Be fully licensed and ready for highway use, on its wheels or jacking system, is attached to the site only by quick disconnect type utilities and security devices, and has no permanently attached additions; or

iii) Meet the requirements of 5.5(1) and 5.5(3) above and the anchoring requirements for manufactured homes (Section 5.1-1(2)).