Chapter 16C.05.28
FLOOD HAZARD PROTECTION STANDARDS

Sections:

16C.05.28.010    General Standards.

16C.05.28.020    Specific Standards.

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 shall be:

(i)    Anchored to prevent flotation, collapse or lateral movement of the structure; 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 equal to 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.

(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.

(3)    Subdivision Proposals. Subdivision proposals 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 flood damage;

(c)    Have adequate drainage provided to reduce exposure to flood damage; and

(d)    Include base flood elevation data.

(4)    Watercourse Alterations. The flood-carrying capacity within altered or relocated portions of any watercourse shall be maintained. 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.

(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, 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)    New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated at a minimum to or above the base flood elevation.

(b)    Fully enclosed areas below the lowest floor that are subject to flooding are prohibited, or 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.

(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).

(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 either have the lowest floor, including basement, elevated a minimum of one foot above the base flood elevation; or, together with attendant utility and sanitary facilities, shall:

(a)    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; and

(b)    Have structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy;

(c)    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;

(d)    Nonresidential structures that are elevated, not floodproofed, must meet the same standards for space below the lowest floor as described in Section 16C.05.28.020(1)(b) above;

(e)    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;

(f)    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. Agricultural construction or other accessory structures that constitute a minimal investment and comply with the floodway encroachment standards may be exempt from the floodproofing and elevation requirements of subsection (2) above when such structures, together with attendant utility sanitary facilities:

(a)    Have a low potential for structural flood damage;

(b)    Are designed and oriented to allow the free passage of floodwaters through the structure in a manner affording minimum flood damage; and

(c)    Ensure that all electrical and mechanical equipment subject to floodwater damage and permanently affixed to the structure be elevated a minimum of one foot above the base flood elevation or higher, or floodproofed;

(d)    Are constructed and placed on the building site so as to offer the minimum resistance to the flow of floodwaters; and

(e)    Will not be used for human habitation.

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)    Manufactured homes shall be anchored in accordance with Section 16C.05.28.010(1)(b), shall have the lowest floor elevated to or 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).

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