19.74.050 Provisions for flood hazard reduction

19.74.050 Provisions for flood hazard reduction.

A. General Standards. In all areas of special flood hazards, the following standards are required:

a. All new construction and substantial improvements shall be anchored to prevent flotation, collapse, or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads including effects of buoyancy.

b. All manufactured homes must likewise be anchored to prevent flotation, collapse, or lateral movement, and shall be installed using methods and practices that minimize flood damage. Anchoring methods may include, but are not limited to, use of over-the-top or frame ties to ground anchors (reference FEMA’s “Manufactured Home Installation in Flood Hazard Areas” guidebook for additional techniques).

a. All new construction and substantial improvements shall be constructed with materials and utility equipment resistant to flood damage.

b. All new construction and substantial improvements shall be constructed using methods and practices that minimize flood damage.

c. Electrical, heating, ventilation, plumbing, and air-conditioning equipment and other service facilities shall be designed and/or otherwise elevated or located so as to prevent water from entering or accumulating within the components during conditions of flooding.

a. All new and replacement water supply systems shall be designed to minimize or eliminate infiltration of floodwaters into the systems;

b. The proposed water well shall be located on high ground that is not in the floodway (WAC 173-160-171);

c. New and replacement sanitary sewage systems shall be designed to minimize or eliminate infiltration of floodwaters into the systems and discharges from the systems into floodwaters; and

d. On-site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding.

a. All subdivision proposals shall be consistent with the need to minimize flood damage;

b. All subdivision proposals shall have public utilities and facilities, such as sewer, gas, electrical, and water systems located and constructed to minimize or eliminate flood damage;

c. All subdivision proposals shall have adequate drainage provided to reduce exposure to flood damage; and

d. Where base flood elevation data has not been provided or is not available from another authoritative source, it shall be generated for subdivision proposals and other proposed developments which contain at least 50 lots or five acres (whichever is less).

5. Review of Building Permits. Where elevation data is not available either through the Flood Insurance Study, FIRM, or from another authoritative source (AMC 19.74.040(C)(2)), applications for building permits shall be reviewed to assure that proposed construction will be reasonably safe from flooding. The test of reasonableness is a local judgment and includes use of historical data, high water marks, photographs of past flooding, etc., where available. Failure to elevate at least two feet above the highest adjacent grade in these zones may result in higher insurance rates.

B. Specific Standards. In all areas of special flood hazards where base flood elevation data has been provided (Zones A1-30, AH, and AE) as set forth in AMC 19.74.030(B), Basis for Establishing the Areas of Special Flood Hazard, or 19.74.040(C)(2), Use of Other Base Flood Data (In A and V Zones), the following provisions are required:

a. In AE and A1-30 Zones or other A Zoned areas where the BFE has been determined or can be reasonably obtained, new construction and substantial improvement of any residential structure must have the lowest floor, including basement, elevated two feet or more above the BFE. Mechanical equipment and utilities must be waterproof or elevated one foot above BFE.

b. New construction and substantial improvement of any structure in an unnumbered A Zone for which a BFE is not available and cannot be reasonably obtained must be reasonably safe from flooding, but in all cases the lowest floor must be at least two feet above the highest adjacent grade.

c. New construction and substantial improvement of any residential structure in a V, V1-30, or VE Zone must meet the requirements of subsection (C) of this section, Coastal High Hazard Areas.

d. Fully enclosed areas below the lowest floor that are subject to flooding are prohibited or must designed to automatically equalize hydrostatic flood forces on the exterior walls by allowing for the entry and exit of floodwaters. Designs must meet or exceed the following criteria or be designed by a registered engineer or architect and certify engineered openings:

i. Have a minimum of two openings with a total net area of not less than one square inch for every square foot of enclosed area subject to flooding.

ii. The bottom of all openings must be no higher than one foot above grade.

iii. Openings may be equipped with screens, louvers, valves or other coverings or devices provided they permit the automatic entry and exit of floodwaters.

iv. A garage attached to a residential structure, constructed with the garage floor slab below the BFE, must be designed to allow for the automatic entry and exit of floodwaters.

2. Nonresidential Construction. Nonresidential construction or substantial improvement of any commercial, industrial, or other nonresidential structure must meet the requirements of subsection (B)(2)(a) or (b) below.

a. New construction and substantial improvement of any commercial, industrial, or other nonresidential structure must meet all the following requirements:

i. In AE and A1-30 Zones or other A Zoned areas where the BFE has been determined or can be reasonably obtained, new construction and substantial improvement of any commercial, industrial, or other nonresidential structure must have the lowest floor, including basement, elevated two feet or more above the BFE, or elevated as required by ASCE 24, whichever is greater. Mechanical equipment and utilities must be waterproofed or elevated at least one foot above, or as required by ASCE 24, whichever is greater.

ii. If located in an unnumbered A Zone for which a BFE is not available and cannot be reasonably obtained, the structure must be reasonably safe from flooding, but in all cases the lowest floor must be at least two feet above the highest adjacent grade.

iii. If located in a V, V1-30 or VE Zone, the structure must meet the requirements of subsection (C) of this section, Coastal High Hazard Areas.

b. Fully enclosed areas below the lowest floor that are subject to flooding are prohibited or must meet be designed to automatically equalize hydrostatic flood forces on the exterior walls by allowing for the entry and exit of flood forces. Designs for meeting this requirement must either be certified by a registered professional engineer or architect or must meet or exceed the following minimum criteria or be designed by a registered engineer or architect and certify engineered openings:

i. Have a minimum of two openings with a total net area of not less than one square inch for every square foot of enclosed area subject to flooding.

ii. The bottom of all openings must be no higher than one foot above grade.

iii. Openings may be equipped with screens, louvers, valves or other coverings or devices provided that they permit the automatic entry and exit of floodwater.

iv. A garage attached to a nonresidential structure, constructed with the garage floor slab below the BFE, must be designed to allow for the automatic entry and exit of floodwater.

c. If the requirements of subsection (B)(2)(a) of this section are not met, then the new construction and substantial improvement of any commercial, industrial, or other nonresidential structure must meet all the following requirements:

i. Be dry flood proofed so that one foot or more above the base flood level the structure is watertight with walls substantially impermeable to the passage of water or dry flood proofed to the elevation required by ASCE 24, whichever is greater;

ii. Have structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy;

iii. Be certified by a registered professional engineer or architect that the design and methods of construction are in accordance with accepted standards of practice for meeting provisions of this subsection based on their development and/or review of the structural design, specifications, and plans. Such certifications must be provided to the official as set forth in AMC 19.74.040(C)(3);

iv. Nonresidential structures that are elevated, not flood proofed, must meet the same standards for space below the lowest floor as described in subsection (B)(2)(b) of this section;

v. Applicants who are flood proofing nonresidential buildings must be notified that flood insurance premiums will be based on rates that are one foot below the flood proofed level (e.g., a building that is flood proofed to the base flood level will be rated as one foot below). Flood proofing the building an additional foot will reduce flood insurance premiums.

a. All manufactured homes to be placed or substantially improved on sites:

i. Outside of a manufactured home park or subdivision;

ii. In a new manufactured home park or subdivision;

iii. In an expansion to an existing manufactured home park or subdivision; or

iv. In an existing manufactured home park or subdivision on which a manufactured home has incurred “substantial damage” as the result of a flood;

shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is elevated one foot or more above the base flood elevation and be securely anchored to an adequately designed foundation system to resist flotation, collapse, and lateral movement.

b. Manufactured homes to be placed or substantially improved on sites in an existing manufactured home park or subdivision that are not subject to the above manufactured home provisions shall be elevated so that either:

i. The lowest floor of the manufactured home is elevated one foot or more above the base flood elevation; or

ii. The manufactured home chassis is supported by reinforced piers or other foundation elements of at least equivalent strength that are no less than 36 inches in height above grade and is securely anchored to an adequately designed foundation system to resist flotation, collapse, and lateral movement.

4. Recreational Vehicles. Recreational vehicles placed on sites are required to either:

a. Be on the site for fewer than 180 consecutive days;

b. Be fully licensed and ready for highway use, on its wheels or jacking system, be attached to the site only by quick disconnect type utilities and security devices, and have no permanently attached additions; or

c. Meet the requirements of subsection (B)(3) of this section and the elevation and anchoring requirements for manufactured homes.

5. Enclosed Area Below the Lowest Floor. If buildings or manufactured homes are constructed or substantially improved with fully enclosed areas below the lowest floor, the areas must be used for parking of vehicles, building access, or storage.

a. Appurtenant structures used solely for parking of vehicles or limited storage may be constructed such that the floor is below the BFE, provided the structure is designed and constructed in accordance with the following requirements:

i. Use of the appurtenant structure must be limited to parking of vehicles or storage;

ii. The portions of the appurtenant structure located below the BFE must be built using flood resistant materials;

iii. The appurtenant structure must be anchored to prevent flotation, collapse, and lateral movement;

iv. Any machinery or equipment servicing the appurtenant structure must be elevated or flood proofed to or above BFE;

v. The appurtenant structure must be designed to allow for the automatic entry and exit of floodwaters in accordance with subsection (B)(1)(d) of this section;

vi. The structure must have low damage potential;

vii. If the structure converted to another use, it must be brought into full compliance with standards governing such use;

viii. The structure must not be used for human habitation.

b. Detached garages, storage structures, and other appurtenant structures not meeting the above standards must be constructed in accordance with all applicable standards in subsection (B)(1)(d) of this section.

c. Upon completion of the structure, certification that the requirement of this section has been satisfied must be provided to the Floodplain Administrator for verification.

7. AE and A1-30 Zones With Base Flood Elevations but No Floodways. In areas with BFEs (when a regulatory floodway has not been designated), no new construction, substantial improvements, or other development (including fill) shall be permitted within Zones A1-30 and AE on the community’s FIRM, unless it is demonstrated that the cumulative effect of the proposed development, when combined with all other existing and anticipated development, will not increase the water surface elevation of the base flood more than one foot at any point within community.

C. Coastal High Hazard Areas. Located within areas of special flood hazard established in AMC 19.74.030(B) are coastal high hazard areas, designated as Zones V1-30, VE and/or V. These areas have special flood hazards associated with high velocity waters from surges and, therefore, in addition to meeting all provisions in this chapter, the following provisions shall also apply:

1. All new construction and substantial improvements in Zones V1-30 and VE (V if base flood elevation is available) on the community’s FIRM must be elevated on pilings and columns so that:

a. For residential buildings the bottom of the lowest horizontal structural member of the lowest floor (excluding the pilings or columns) is elevated one foot or more above the base flood level.

b. For nonresidential buildings the bottom of the lowest horizontal member of the lowest floor (excluding pilings or columns) is elevated one foot or more above the base flood level or meets the requirements of ASCE 24, whichever is higher.

c. The pile or column foundation and structure attached thereto is anchored to resist flotation, collapse, and lateral movement due to the effects of wind and water loads acting simultaneously on all building components. Wind and water loading values shall each have a one percent chance of being equaled or exceeded in and given year (100-year mean recurrence interval).

d. A registered professional engineer or architect shall develop or review the structural design, specifications and plans for the construction, and shall certify that the design and methods of construction to be used are in accordance with accepted standards of practice for meeting the provisions of this section;

2. The elevation (in relation to mean sea level) of the bottom of the lowest structural member of the lowest floor (excluding pilings and columns) of all new and substantially improved structures in Zones V1-30, VE, and V on the community’s FIRM and whether or not such structures contain a basement shall be provided to the Administrator. The Administrator shall maintain a record of all such information;

3. All new construction within Zones V1-30, VE, and V on the community’s FIRM shall be located landward of the reach of mean high tide;

4. All new construction and substantial improvements within Zones V1-30, VE, and V on the community’s FIRM must have the space below the lowest floor either free of obstruction or constructed with nonsupporting breakaway walls, open wood latticework, or insect screening intended to collapse under wind and water loads without causing collapse, displacement, or other structural damage to the elevated portion of the building or supporting foundation system. For the purposes of this section, a breakaway wall shall have a design safe loading resistance of not less than 10 and no more than 20 pounds per square foot. Use of breakaway walls which exceed a design safe loading resistance of 20 pounds per square foot (either by design or when so required by local or state codes) may be permitted only if a registered professional engineer or architect certifies that the designs proposed meet the following conditions:

a. Breakaway wall collapse shall result from water load less than that which would occur during the base flood, and

b. The elevated portion of the building and supporting foundation system shall not be subject to collapse, displacement, or other structural damage due to the effects of wind and water loads acting simultaneously on all building components (structural and nonstructural). Maximum wind and water loading values to be used in this determination shall each have a one percent chance of being equaled or exceeded in any given year (100-year mean recurrence interval).

If breakaway walls are utilized, such enclosed space shall be useable solely for parking of vehicles, building access, or storage. Such space shall not be used for human habitation;

5. The use of fill for structural support of buildings within Zones V1-30, VE, and V on the community’s FIRM is prohibited;

6. Human-caused alteration of sand dunes within Zones V1-30, VE, and V on the community’s FIRM which would increase potential flood damage is prohibited;

7. All manufactured homes to be placed or substantially improved within Zones V1-30, V, and VE on the community’s FIRM on sites:

a. Outside of a manufactured home park or subdivision,

b. In a new manufactured home park or subdivision,

c. In an expansion to an existing manufactured home park or subdivision, or

d. In an existing manufactured home park or subdivision on which a manufactured home has incurred “substantial damage” as the result of a flood,

shall meet the standards of subsections (C)(1) through (C)(6) of this section and manufactured homes placed or substantially improved on other sites in an existing manufactured home park or subdivision within Zones V1-30, V, and VE on the FIRM meet the requirements of subsection (B)(3) of this section;

8. Recreational vehicles placed on sites within Zones V1-30, V, and VE on the community’s FIRM must either:

a. Be on the site for fewer than 180 consecutive days,

b. Be fully licensed and ready for highway use, on its wheels or jacking system, attached to the site only by quick disconnect type utilities and security devices, and have no permanently attached additions, or

c. Meet the requirements of AMC 19.74.040(A)(1), Development Permit Required, and subsections (C)(1) through (C)(6) of this section.

D. Critical Facility. Construction of new critical facilities shall be, to the extent possible, located outside the limits of the special flood hazard area (SFHA) (100-year floodplain). Construction of new critical facilities shall be permissible within the SFHA if no feasible alternative site is available. Critical facilities constructed within the SFHA shall have the lowest floor elevated three feet or to the height of the 500-year flood, whichever is higher. Access to and from the critical facility should also be protected to the height utilized above. Flood proofing and sealing measures must be taken to ensure that toxic substances will not be displaced by or released into floodwaters. Access routes elevated to or above the level of the base flood elevation shall be provided to all critical facilities to the extent possible. (Ord. 4016 § 2 (Att. A), 2022; Ord. 3064 § 2 (Att. A), 2021; Ord. 2794 § 1 (Att. A), 2008; Ord. 2702 § 3, 2005. Formerly 17.70.060)