16.36.120 General standards | Issaquah Municipal Code

16.36.120 General standards.

In all areas of special flood hazards, the following standards are required:

1. 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 the effects of buoyancy.

2. 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).

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

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

3. 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.

C. Crawlspaces. Crawlspaces are allowed in residential and nonresidential construction only where the difference in elevation between the crawlspace interior grade and lowest adjacent exterior grade is 2 feet or less, the total height of the crawlspace as measured from the interior grade of the crawlspace to the bottom of the floor joists is 4 feet or less, and adequate drainage is provided to remove floodwaters within a reasonable amount of time after a flood event. Interpretation and application of these requirements shall be consistent with official FEMA technical bulletin guidance on crawlspace construction. Other types of foundations, such as open pile or column foundations, that allow free-flow of floodwaters may be required in high velocity areas (i.e., velocities exceeding 5 feet per second). Below grade crawlspaces constructed in accordance with these requirements will not be considered basements. Crawlspaces that are excavated below grade will result in higher flood insurance premiums.

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

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

3. On-site disposal systems shall be located to avoid impairment to them or contamination from them during flooding. On-site disposal systems require permits and approval by Seattle-King County Department of Public Health.

4. Utility transmission lines transporting hazardous substances shall be buried at a minimum depth of 4 feet below the maximum depth of scour for the base flood as predicted by a Washington State licensed professional civil engineer and shall achieve sufficient negative buoyancy so that any potential for flotation or upward migration is eliminated.

5. Water wells shall be located on high ground that is not in the floodway.

E. Development proposals, including subdivisions and manufactured home parks or subdivisions, shall:

1. Be consistent with the need to minimize flood damage.

2. Have public utilities and facilities such as sewer, gas, electrical and water systems located and constructed to minimize flood damage.

3. Have adequate drainage provided to reduce exposure to flood damage.

4. Main collector roads serving new subdivisions shall have a surface elevation high enough to be safely used for evacuation in the event of a 100-year flood. In addition, all roads serving new subdivisions shall be of sufficient width to allow parking of vehicles and access for emergency vehicles during periods of inundation.

5. Where base flood elevation data has not been provided or is not available from another authoritative source, it shall be generated by the applicant for development proposals and other proposed developments which contain at least 2 lots or 2 acres, whichever is the lesser.

F. Review of Building Permits. Where base flood elevation data is not available, either through the Flood Insurance Study or from another authoritative source (IMC 16.36.210(B)), 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 the lowest floor at least 2 feet above the highest existing grade may result in higher insurance rates.

G. Channel Migration and Bank Stabilization. No structure shall be allowed which would be at risk due to stream bank destabilization including that associated with channel relocation or meandering.

H. Temporary Structures. Temporary structures that do not have footings, foundations, or other anchorage to prevent flotation, collapse or movement of the structure during floods shall be removed from the floodplain during the flood season from September 30th to May 1st.

I. Flood Walls. No flood walls are allowed except if constructed within 3 feet of a flood-prone structure that is not built to current flood standards. Flood walls shall be designed by a qualified engineer to withstand hydrostatic pressures and undermining of footings. Flood walls are also subject to the floodway encroachment standard in IMC 16.36.140, and reduction in floodplain conveyance and storage due to flood wall construction shall require mitigation. A flood wall is not meant to include a building wall or foundation that is associated with an approved structure. Applicants constructing flood walls shall be notified that flood insurance premiums for residential structures will still be based on lowest floor elevations regardless of the effect of the flood wall.

J. Flood Hazard Notification. Base flood data and flood hazard notes shall be shown on the face of the recorded plat, including, but not limited to, the base flood elevation, required flood protection elevations, and the boundaries of the floodplain. The following note, or similar language, shall appear on the face of the recorded plat and on the individual titles for all affected lots:

NOTICE

Lots and structures located within flood hazard areas may be inaccessible by emergency vehicles and personnel during flood events. Residents and property owners should take appropriate advance precautions. Property damage and personal safety risks may occur.

1. A permit application to develop in the regulatory floodplain shall include an assessment of the impact of the project on Federal, State or locally protected species and habitat, pursuant to the Endangered Species Act (ESA) as implemented by FEMA Region X under the National Flood Insurance Program for Puget Sound. The applicant shall submit sufficient information to support the assessment, in the form of a checklist, habitat assessment, biological opinion, or other documentation. The City will determine the submittal and review requirements depending on the nature and extent of the project. The City may require a habitat assessment or biological opinion prepared by a consultant, or peer review by a consultant not associated with an applicant. This additional peer review shall be at the applicant’s expense.

2. ESA review under a Federal permit, such as through the U.S. Army Corps of Engineers or through another Federal consultation process, meets the requirement for a habitat impact assessment under this subsection K and no additional submittal or review is required. Proof of such Federal review shall be submitted.

3. If the habitat impact assessment submitted to the City (or through any other ESA review process such as a Federal permit) concludes that the project is expected to have an adverse effect on listed species as evaluated under the guidance issued for ESA compliance under the National Flood Insurance Program in Puget Sound, the applicant shall mitigate those impacts. Such mitigation shall be consistent with, or in addition to, any mitigation required by critical area regulations in Chapter 18.802 IMC or other City mitigation requirements and shall be incorporated into the approved project plans.

4. Activities Exempt From Habitat Impact Assessment. The following activities within a floodplain are deemed to have no impact on listed species and are exempt from the habitat impact assessment requirements in this subsection K:

a. Repair or remodeling of an existing structure, if the repair or remodeling is not a substantial improvement, or a repair of substantial damage.

b. Expansion of an existing structure that is no greater than 10 percent beyond its existing footprint; provided, that the repairs or remodeling is not a substantial improvement, or a repair of substantial damage. This measurement is counted cumulatively from September 22, 2011. If the structure is in the floodway, there shall be no change in the dimensions perpendicular to flow.

c. Activities with the sole purpose of creating, restoring, or enhancing natural functions provided the activities do not include structures, grading, fill, or impervious surfaces.

d. Development of open space and recreational facilities, such as parks and trails, that do not include structures, fill, impervious surfaces or removal of more than five percent of the native vegetation on that portion of the property in the regulatory floodplain.

e. Repair to on-site septic systems provided the ground disturbance is the minimum necessary.

f. Alterations in response to emergencies which threaten the public health, safety and welfare or which pose an imminent risk of damage to private property consistent with the requirements of Chapter 18.800 IMC.

g. Other minor activities considered to have no effect on listed species, as interpreted using ESA guidance issued by the National Flood Insurance Program in Puget Sound and confirmed through City review of the development proposal.

1. If a project will alter the BFE or boundaries of the SFHA, then the project proponent shall provide the community with engineering documentation and analysis regarding the proposed change. If the change to the BFE or boundaries of the SFHA would normally require a letter of map change, then the project proponent shall initiate, and receive approval of, a conditional letter of map revision (CLOMR) prior to approval of the development permit, where required by the Federal Emergency Management Agency. The project shall be constructed in a manner consistent with the approved CLOMR.

2. If a CLOMR application is made, then the project proponent shall also supply the full CLOMR documentation package to the Floodplain Administrator to be attached to the floodplain development permit, including all required property owner notifications.

1. The storage or processing of materials that could be injurious to human, animal, or plant life if released due to damage from flooding is prohibited in special flood hazard areas.

2. Storage of other material or equipment may be allowed if elevated at or above the flood protection elevation level, not subject to damage by floods, and if firmly anchored to prevent flotation, or if readily removable from the area within the time available after flood warning. (Ord. 3023 § 32, 2023; Ord. 2989 § 3 (Exh. A3), 2022; Ord. 2915 § 1 (Exh. A), 2020; Ord. 2775 § 1 (Exh. A), 2016; Ord. 2420 § 1, 2005; Ord. 2030 § 6, 1994; Ord. 1827 § 7, 1989; Ord. 1465 § 7(A), 1981).