Gresham, OR Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Freeboard required
- 1 foot above base flood elevation
- Applies to
- New and substantially improved structures
- Flood vent size
- 1 sq in per sq ft
- Vent height limit
- No higher than 1 ft above grade
- Governing section
- Dev. Code § 5.0120(E)(1)
Summary
New and substantially improved homes in Gresham's Floodplain Overlay District must have their lowest floor built at least one foot above the base flood elevation, the city's mandatory freeboard standard.
New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated to or above base flood elevation plus one foot.
2. 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:
a. 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.
b. The bottom of all openings shall be no higher than one foot above 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.
3. Below grade crawl spaces are allowed subject to the current Oregon Residential Specialty Code Section R324.
4. Development in the AH zone shall provide drainage paths around structures on slopes to guide floodwaters around and away from proposed structures.
City of Gresham Development Code
[5.0100]-4
(06/26)
Full Breakdown
Gresham Community Development Code § 5.0120(E)(1) requires new construction and substantial improvements to any residential structure in the Floodplain Overlay District to elevate the lowest floor, including any basement, to or above base flood elevation plus one foot of freeboard. Enclosed areas below that floor must either be avoided or fitted with flood vents, at least two openings totaling one square inch of net area per square foot of enclosed space, with the lowest opening no higher than one foot above grade, so floodwaters can enter and exit without collapsing the structure. Non-residential buildings face an equivalent elevation or floodproofing standard under § 5.0120(F)(1).
Violations & Fines
Building below the required base-flood-elevation-plus-one-foot mark, or leaving enclosed lower areas without compliant flood vents, is a Development Code violation the Manager can catch at permit review or through a stop-work order.
Frequently Asked Questions
How high above flood level must a Gresham home be built?
What about crawl spaces or enclosed areas below the elevated floor?
Sources & Official References
Other rules in Gresham
Compare Gresham to another location·View the Oregon environmental rules overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.
Flood Elevation Requirements in Nearby Cities
How other cities in Multnomah County handle flood elevation requirements.