Chapter 16C.05.28 FLOOD HAZARD PROTECTION STANDARDS

Chapter 16C.05.28
FLOOD HAZARD PROTECTION STANDARDS

Sections:

16C.05.28.010 General Standards.

The following regulations shall apply in all special flood hazard areas:

(1) Anchoring and Construction Techniques.

(a) All new construction and substantial improvements, including those related to manufactured homes, shall be:

(i) Anchored to prevent flotation, collapse or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads including the effects of buoyancy; and

(ii) Constructed using materials and utility equipment resistant to flood damage; and

(iii) Constructed using methods and practices that minimize flood damage; and

(iv) 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.

(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). Anchoring shall meet the specifications set forth below for structures located within one hundred feet of a floodway or the ordinary high water mark if no floodway has been established.

(c) All new construction and any improvements or additions to existing floodproofed structures that would extend beyond the existing floodproofing located within one hundred feet of the floodway or one hundred feet of the ordinary high water mark if no floodway has been established shall be elevated to a height one foot or greater than the base flood, using zero-rise methods such as piers, posts, columns, or other methodology, unless it can be demonstrated that non-zero-rise construction methods will not impede the movement of floodwater or displace a significant volume of water. The size and spacing of any support devices used to achieve elevation shall be designed to penetrate bearing soil, and be sufficiently anchored, as specified above in subsection (1)(a) of this section, provided therefrom, if the original building required a floodproofing certificate, then the floodproofing certificate must be updated. Also provided therefrom, if any part of the project is in a floodway, the floodway standards in this code still apply.

(d) Except where otherwise authorized, all new construction and substantial improvements to existing structures shall require certification by a registered professional engineer, architect or surveyor that the design and construction standards are in accordance with adopted floodproofing techniques.

(2) Utilities.

(a) All new and replacement water supply systems and sanitary sewage systems shall be designed to minimize or eliminate infiltration of floodwaters into the systems and discharge from the systems into floodwaters; and on-site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding. Water wells shall be located on high ground that is not in the floodway.

(3) Subdivision Proposals and Development. Subdivision proposals, as well as new development shall:

(a) Be consistent with the need to minimize flood damage;

(b) Have roadways, public utilities and other facilities such as sewer, gas, electrical, and water systems located and constructed to minimize or eliminate flood damage;

(d) Where subdivision proposals and other proposed developments contain greater than 50 lots or 5 acres (whichever is lesser) base flood elevation data shall be included as part of the application.

(4) Watercourse Alterations. Whenever a watercourse is to be altered or relocated:

(a) Assure that the flood-carrying capacity within altered or relocated portions of any watercourse shall be maintained.

(b) Prior to the approval of any alteration or relocation of a watercourse in riverine situations, the department shall notify adjacent communities the Department of Ecology and FEMA of the proposed development and submit evidence of such notification to the Federal Insurance Administrator through appropriate notification means.

(Ord. 8-2021 § 2(C) (Exh. 1), 2021; Ord. 5-2017 § 2(C) (Exh. 1) (part), 2017: Ord. 13-2007 §1 (Exh. A)(16C.05.28.010), 2007).

16C.05.28.020 Specific Standards.

In all special flood hazard areas where base elevation data has been provided as set forth in Section 16C.05.20.010 or Section 16C.05.44.060, the following regulations shall apply, in addition to the general regulations of Section 16C.05.28.010:

(1) Residential Construction. (Ref. IRC 323.2.)

(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 shall have the lowest floor, including basement, elevated one foot or more above the base flood elevation. Mechanical equipment and utilities shall be waterproofed or elevated at least one foot above the BFE.

(b) Fully enclosed areas below the lowest floor that are subject to flooding are prohibited, or if used solely for parking, access or storage shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. 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:

(i) A minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding shall be provided.

(ii) The bottom of all openings shall be no higher than one foot above grade.

(iii) Openings may be equipped with screens, louvers, or other coverings or devices, provided that 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.

Alternatively, a registered engineer or architect may design and certify engineered openings.

(c) Residential construction within one hundred feet of a floodway or the ordinary high water mark, if no floodway has been established, shall also meet the requirements of Section 16C.05.28.010(1)(c).

(d) New construction and substantial improvement of any residential structure in an AO zone shall meet the requirements in Appendix C.

(e) New construction and substantial improvement of any residential structure in an Unnumbered A zone for which a BFE is not available and cannot be reasonably obtained shall be reasonably safe from flooding, but in all cases the lowest floor shall be at least two feet above the Highest Adjacent Grade.

(2) Nonresidential Construction. New construction and substantial improvement of any commercial, industrial or other nonresidential structure, and any addition to an existing floodproofed structure that would extend beyond the existing floodproofing, shall meet the requirements of subsection (a) or (b) below.

(a) New construction and substantial improvement of any commercial, industrial or other nonresidential structure shall meet all of 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 shall have the lowest floor, including basement, elevated a minimum of one foot above the base flood elevation, or elevated as required by ASCE 24, whichever is greater. Mechanical equipment; and utilities shall be waterproofed or elevated at least one foot above the BFE, or as required by ASCE 24, whichever is greater.

(ii) If located in an AO zone, the structure shall meet requirements in Appendix C.

(iii) If located in an Unnumbered A zone for which a BFE is not available and cannot be reasonably obtained, the structure shall be reasonably safe from flooding, but in all cases the lowest floor shall be at least two feet above the Highest Adjacent Grade.

(iv) Fully enclosed areas below the lowest floor that are subject to flooding are prohibited, or if used solely for parking, access or storage shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. 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:

(A) 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.

(B) The bottom of all openings shall be no higher than one foot above grade.

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

(D) 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.

Alternatively, a registered engineer or architect may design and certify engineered openings.

(b) If the requirements of subsection (a) are not met, then new construction and substantial improvement of any commercial, industrial or other nonresidential structure shall meet all of the following requirements:

(i) Be floodproofed so that below an elevation one foot above base flood level the structure is watertight, with walls substantially impermeable to the passage of water or dry floodproofed 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 method 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 shall be provided to the building official;

(iv) Nonresidential structures that are elevated, not floodproofed, must meet the same standards for space below the lowest floor as described in subsection (2)(a)(iv) above;

(v) Meet the special standards for structures set forth in Section 16C.05.28.010(1)(c) above if within one hundred feet of a floodway or within one hundred feet of the ordinary high water mark and no floodway has been established;

Applicants floodproofing nonresidential buildings shall be notified that flood insurance premiums will be based on rates that are one foot below the floodproofed level (e.g., a building constructed to the base flood level will be rated as one foot below the level). Floodproofing the building an additional foot will reduce insurance premiums significantly. (Ref. IBC 1612.5.)

(3) Agricultural Construction. New construction and substantial improvement of any agricultural structure shall either have the lowest floor, including basement, elevated at a minimum to or above the base flood elevation; or meet the floodproofing requirements of subsection (2) of this section.

All such structures shall be anchored to resist flotation, collapse, and lateral movement, and that only flood resistant materials be used for elements of these buildings below the base flood elevation.

(4) Manufactured Homes.

(a) All manufactured homes to be placed or substantially improved on sites shall have the lowest floor elevated one foot or more above the base flood elevation, and shall be securely anchored to an adequately anchored foundation system to resist flotation, collapse and lateral movement in accordance with Section 16C.05.28.010(1)(b).

(5) Recreational Vehicles. Recreational vehicles placed on sites are required to either:

(a) Be on the site for fewer than 180 days, or

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

(6) 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 shall be used solely for parking of vehicles, building access, or storage.

(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 the community.

(8) Livestock Sanctuary Areas. Elevated areas for the purpose of creating a flood sanctuary for livestock are allowed on farm units where livestock is allowed. Livestock flood sanctuaries shall be sized appropriately for the expected number of livestock and be elevated sufficiently to protect livestock. Proposals for livestock flood sanctuaries shall meet all procedural and substantive requirements of this chapter. To be “elevated sufficiently to protect livestock” typically means to be elevated at least one foot above the BFE.

(Ord. 8-2021 § 2(C) (Exh. 1), 2021; Ord. 5-2017 § 2(C) (Exh. 1) (part), 2017: Ord. 13-2007 §1 (Exh. A)(16C.05.28.020), 2007).