Hillsboro, OR Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Minimum elevation
- 1 ft above Base Flood Elevation
- Non-residential option
- Elevate or floodproof to 1 ft above BFE
- Permit required
- FA II (Type II procedure)
- Elevation certificates filed
- 3 times during construction
- Zone
- Regulatory Floodplain Overlay, outside floodway
- Certifying professional
- Registered civil engineer + land surveyor
Summary
New homes and additions built inside Hillsboro's Regulatory Floodplain Overlay must have the lowest floor, including any basement, elevated at least one foot above the Base Flood Elevation. The standard is enforced through a Floodplain Activity II permit reviewed by the City's Floodplain Administrator before construction begins.
Residential construction is permitted within the RFO outside of the floodway with the approval of a FA II permit. In addition to the general development standards in Section 12.27.130, the following requirements apply:...ii.All new construction, conversion to residential and substantial improvements of any residential structure shall have the lowest floor, including basement, elevated to at least one foot above the Base Flood Elevation.iii.Attached garages may be constructed with the garage floor slab below the Base Flood Elevation if only used for parking, access and/or storage and the floors are at or above grade on at least one side...vi.FEMA Elevation Certificates are required to be filed with the Floodplain Administrator three times due to the importance of verifying elevations before, during, and after construction: (1) prior to issuance of a building permit; (2) upon placement of the lowest floor, including any basement, and prior to further vertical construction; and (3) prior to issuance of a certificate of occupancy or approval of final inspections.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Municipal Code: Supplement 1 | Community Development Code: Supplement 1).
Full Breakdown
3 sets the elevation standard for residential construction inside the Regulatory Floodplain Overlay (RFO), the zone covering the special flood hazard area mapped in the FEMA Flood Insurance Study for Washington County dated October 19, 2018. 040. The lowest floor of any new residential structure, including the basement, must sit at least one foot above the Base Flood Elevation (BFE); attached garages are the one carve-out, allowed with the slab below BFE if used solely for parking, access or storage and with floors at or above grade on at least one side.
A registered professional civil engineer must certify that the structure will not reduce the site's flood-carrying capacity or raise the base flood level. To verify the elevation was actually built as designed, FEMA Elevation Certificates, sealed by a professional land surveyor, must be filed with the Floodplain Administrator three separate times: before the building permit issues, when the lowest floor is placed and before vertical construction continues, and again before a certificate of occupancy or final inspection is approved. 4 follows a parallel rule: the lowest floor must clear one foot above BFE, or the structure and its utility systems must be floodproofed to that same one-foot mark, with FEMA Floodproofing Certificates filed on the same three-stage schedule. 1. A.
Violations & Fines
Community Development Code § 12.01.150 classifies CDC violations, including building below the required Base Flood Elevation without an approved FA II permit, as infractions subject to the City's civil enforcement provisions. Such violations are also declared nuisances and may be abated under Title 6 of the Hillsboro Municipal Code, giving the City a separate nuisance-abatement track alongside the civil infraction process administered by the Floodplain Administrator and Director.
Frequently Asked Questions
How high above the base flood elevation must a new Hillsboro home be built?
What permit does floodplain construction need in Hillsboro?
How many times must an elevation certificate be filed?
What happens if a structure is built below the required elevation?
Sources & Official References
Other rules in Hillsboro
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