16.36.130 Specific standards | Issaquah Municipal Code

16.36.130 Specific standards.

In all areas of special flood hazards designated AE zones or other A zoned areas where base flood elevation data has been provided, or can be reasonably determined, as set forth in IMC 16.36.040 or 16.36.210(B), the following provisions are required:

A. Residential Construction. New construction, substantial improvement of any residential structure, and improvement of any post-FIRM residential structure shall have the lowest floor, including basement and all electrical, heating, ventilation, plumbing, air-conditioning equipment, and other utility and service facilities elevated to at or above the flood protection elevation level.

1. 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 be certified by a registered professional engineer or must meet or exceed the following minimum criteria:

a. A minimum of 2 openings having a total net free area of not less than 1 square inch for every square foot of enclosed area subject to flooding shall be provided;

b. The bottom of all openings shall be no higher than 1 foot above the adjacent exterior grade;

c. Openings may be equipped with screens, louvers, or other coverings or devices; provided, that they permit the automatic entry and exit of floodwaters; and provided, that the screens, louvers, or other devices meet the requirements of the International Building Code;

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.

2. New construction and substantial improvement of any residential structure in an AO zone shall meet the requirements in IMC 16.36.145.

3. 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 and all electrical, heating, ventilation, plumbing, air-conditioning equipment, and other utility and service facilities shall be at least elevated at or above the flood protection elevation level.

B. Nonresidential Construction. New construction and substantial improvement of any commercial, industrial or other nonresidential structure shall meet the requirements of subsection (B)(1) or (2) of this section:

1. New construction and substantial improvement of any commercial, industrial or other nonresidential structure, together with attendant utility and sanitary facilities, shall meet all of the following requirements:

a. In AE zones and A zoned areas where the BFE has been determined or can be reasonably obtained: New construction, substantial improvement of any commercial, industrial or other nonresidential structure, and improvement of any post-FIRM commercial, industrial or other nonresidential structure shall either have the lowest floor, including basement, and all electrical, heating, ventilation, plumbing, air-conditioning equipment, and other utility and service facilities elevated at or above the flood protection elevation level, or as required by ASCE 24, whichever is greater;

b. If located in an AO zone, the structure shall be at or above the depth number specified on the FIRM and meet the requirements in IMC 16.36.145.

c. 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 or above the flood protection elevation level.

d. Fully enclosed areas below the lowest floor that are subject to flooding are prohibited, or if used 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. Have a minimum of 2 openings with a total net area of not less than 1 square inch for every square foot of enclosed area subject to flooding.

ii. The bottom of all openings shall be no higher than 1 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.

2. If the requirements of subsection (B)(1) of this section are not met, then new construction and substantial improvement of any commercial, industrial or other nonresidential structure shall meet all of the following requirements:

a. Be dry floodproofed at or above the base flood level so that the structure is watertight with walls substantially impermeable to the passage of water;

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

c. Be certified by a registered professional engineer 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 shall be provided to the official as set forth in IMC 16.36.210(C)(2);

d. Be certified by a registered professional engineer 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 shall be provided to the official as set forth in IMC 16.36.210(C)(2);

e. Applicants floodproofing nonresidential buildings shall be notified that flood insurance premiums will be based on rates that are 1 foot below the floodproofed level (e.g., a building constructed to the base flood level will be rated as 1 foot below that level).

C. Compensatory Storage and No Reduction in Floodplain Conveyance Required. Development proposals shall not reduce the effective base flood storage volume of the floodplain, and also shall not reduce the hydraulic capability of the floodplain on site to convey floodwaters through the property during the base flood event. The compensatory storage requirement means that the project shall not result in any additional net fill within the floodplain. No reduction in floodplain conveyance means that no rise in base flood elevations is allowed on adjacent properties. Providing this compensatory conveyance capacity can be done in conjunction with the compensatory storage. Compensatory storage can be provided either on site or at a hydraulically connected off-site location, and can be obtained from a previous project that was constructed by the applicant or by another owner who provides written permission; provided, that excess and unused compensatory storage is available from that project. A floodplain hydraulic study prepared by a licensed civil engineer registered in the State of Washington may be required to verify compliance with the compensatory storage and compensatory conveyance requirements. Certification by the engineer that appropriate hydraulic modeling methods were used to comply with these requirements shall accompany the flood hazard permit. In lieu of an engineering study the applicant must be able to provide adequate information that demonstrates an understanding of floodplain conveyance and compliance with this section.

D. Manufactured Homes. All manufactured homes to be placed or substantially improved within all zones on the community’s FIRM shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is at or above the flood protection elevation level and shall be securely anchored to an anchored foundation system to resist flotation, collapse and lateral movement, in accordance with the provisions of IMC 16.36.120(A).

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

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

2. Be fully licensed and ready for highway use, on their 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

3. Meet the requirements for manufactured homes.

F. Bank Improvements. Where proposed development or improvements include modifications or work within the portion of the stream channel under the jurisdiction of the Washington Department of Fish and Wildlife (WDFW), an application shall also be made for a State hydraulics permit approval (HPA), the application for which is through WDFW using a joint aquatic resource permit application (JARPA). Once the State HPA permit is approved, application shall be made for the permit required by this chapter.

G. Critical Facilities. Construction of new critical facilities shall be, to the extent possible, located outside the limits of the base floodplain. Construction of critical facilities shall be permissible within the base floodplain if no feasible alternative site is available. Critical facilities constructed within the floodplain shall have the lowest floor elevated to 3 or more feet above the level of the base flood elevation at the site. Floodproofing and sealing measures must be taken to assure that toxic substances will not be displaced by or released into floodwaters. Access routes elevated to or above the level of the base floodplain shall be provided to all critical facilities to the extent possible.

H. AE Zones with Base Flood Elevations but Not Floodways. In areas with base flood elevations, but where a regulatory floodway has not been designated, no new construction, substantial improvements, or other development (including fill) shall be permitted within Zone AE on the community’s FIRM, unless it has been determined 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 1 foot at any point in the community.

1. In addition to the other requirements in this section, an application for a development activity which results in any change to a regulatory floodway boundary or base flood elevation, or greater than 1/2 foot change to base flood elevations outside of the floodway, shall also submit a request for a conditional letter of map revision (CLOMR), where required by FEMA. The project will not be approved unless FEMA issues the CLOMR (which requires ESA consultation) and the provisions of the letter are made part of the permit requirements.

2. The Director shall notify affected adjacent communities, the Department of Ecology, and FEMA Region X prior to any alteration or relocation of a watercourse, and submit evidence of such notification to the Federal Insurance Administrator through appropriate notification means.

3. The Director shall assure the flood-carrying capacity of the altered or relocated watercourse is maintained.

1. 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:

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

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

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

d. Any machinery or equipment servicing the appurtenant structure must be elevated or floodproofed at or above the flood protection elevation level;

e. The appurtenant structure must comply with floodway encroachment provisions in IMC 16.36.140(A);

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

g. The structure shall have low damage potential;

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

i. The structure shall not be used for human habitation.

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

3. Upon completion of the structure, certification that the requirements of this section have been satisfied shall be provided to the Floodplain Administrator for verification. (Ord. 2989 § 3 (Exh. A3), 2022; Ord. 2915 § 1 (Exh. A), 2020; Ord. 2775 § 1 (Exh. A), 2016; Ord. 2420 § 1, 2005; Ord. 2115 § 1, 1996; Ord. 2065 § 3, 1995; Ord. 2030 § 6, 1994; Ord. 1872 § 7, 1990; Ord. 1465 § 7(B), 1981).