Flood Hazard Permits

If a proposed development is located in a special flood hazard area, also known as the 100-year floodplain or the 1 percent chance flood area, it is subject to review under the flood hazard code requirements contained in in Issaquah Municipal Code Chapter 16.36.

To determine whether your property or structure is located in a floodplain, please contact the Permit Center.

Is Building Allowed in the Floodplain?

Anyone who proposes construction activity in the floodplain, or is considering purchasing land located in the floodplain for future development, should completely understand the City's flood hazard regulations because they can have a tremendous impact on the developability of a parcel of land and remodeling of existing structures. Flood insurance is also required for buildings located in mapped flood hazard areas that have mortgages insured by the Federal government.

In general, development is allowed in floodplains (but not in floodways) if built to floodplain standards. These standards include very specific building requirements such as raising the first floor elevation, how the foundation can be constructed and mitigation requirements to ensure that development does not cause flood elevations to rise on neighboring properties.

Flood Hazard Permit

Flood Hazard Permit Submittal Requirements

Items to submit as part of an application include:

A Flood Hazard Permit is required for activities located in the mapped 100-year floodplain (as defined above) that involve clearing and grading, any new or modified structure, subdivision of land and other activities.

No structures are allowed in the floodway, except bridges, utilities and certain other exceptions as long as they don't cause an increase in flood elevation. In addition, existing structures in floodways cannot be substantially improved except in situations where flood velocities are low.

Mitigation Requirements

The basic mitigation requirements for development in Zone AE areas of the floodplain (i.e., 100-year floodplain, outside of the floodway, with flood elevations determined) are:

  • For new structures, elevate the lowest habitable floor, plus any flood-susceptible utilities (including electrical and mechanical work), a minimum of one foot above the 100-year (base flood) elevation.
  • Commercial structures can be floodproofed, instead of raising the first floor.
  • The specific requirements for improvements to existing structures depends on when the original building was constructed. If built prior to May 1980, the improvements must meet flood standards if the value of improvements is greater than 50 percent of the existing structure's value. For buidings built after May 1980, all improvements must be to flood standards.
  • No fully enclosed spaces below grade, including basements and excavated crawlspaces, are allowed in areas subject to flooding.
  • No displacement of flood waters from fill, structures or foundation systems that would reduce floodplain storage is allowed (i.e., no increase in net fill on the property).
  • No reduction in floodplain conveyance through the property. No reduction in floodplain fill and/or floodplain conveyance often means that structures must be placed on piles.

Keep in mind that meeting these minimum standards will not result in the lowest possible flood insurance premiums for the structure. Higher standards, such as further raising of the first floor and elimination of crawlspace excavation, will improve the flood insurance rating. More information on this can be obtained from flood insurance professionals.

The City also has a few areas mapped as Zone AO, which are areas of shallow flooding (either one- or two-feet depth). Standards are different in these areas, such as fill, which is allowed.

See the Municipal Code sections for full details (the code is included in the permit packet). The Flood Hazard and Building Permit review will evaluate these requirements in detail. The Flood Hazard Permit requires certification by a professional engineer that the proposed development meets the City's code requirements. In many cases (such as projects larger than a single family parcel), a detailed flood study using hydraulic modeling may be required to demonstrate compliance with the no loss in floodplain conveyance requirement.

The FEMA website has technical bulletins that provide detailed information on building in the floodplain. Subjects include floodproofing, foundation venting, crawlspace construction and others.

FEMA Elevation Certificate

All habitable structures, including new and modified buildings, require a Flood Elevation Certificate to provide official documentation - as required by FEMA - of the elevation of that structure's first floor. This requires that the elevation of the floor be surveyed after the structure is built. The Flood Elevation Certificate must be completed and accepted by the City prior to final building permit inspection or Certificate of Occupancy. This form must be completed by a professional land surveyor.