Austin, TX Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Minimum freeboard
- 2 feet above design flood elevation
- Basement floor rule
- 2 feet above design flood elevation
- AO Zone (shallow flooding)
- FIRM depth number plus 2 feet, or 3 feet minimum
- Required documentation
- FEMA Elevation Certificate 086-0-33, PE/surveyor/architect sealed
- Reviewing authority
- Austin Building Official and Floodplain Administrator
- Nonconforming loss trigger
- 90-day discontinuance or 50%+ damage
Summary
Austin's Building Code requires the lowest floor of any new or substantially improved building in a flood hazard area to sit at least two feet above the design flood elevation, with a matching two-foot freeboard added wherever an elevation requirement applies. Basements below grade on every side face the same two-foot floor, and shallow AO Zone lots add a depth-based buffer above adjacent grade.
(1)Elevation Requirements.(a)Unless otherwise specified in Title 25 (Land Development), the lowest floor of a building or structure shall be elevated a minimum of two feet above the design flood elevation.(b)Freeboard. Unless otherwise specified in the Title 25 (Land Development), a minimum freeboard of two foot shall be added where the design flood elevation or other elevation requirements are specified.(c)In areas of shallow flooding (AO Zones), the lowest floor (including a basement) of a building or structure shall be elevated higher than the highest adjacent grade as the depth number specified in feet (mm) on the FIRM plus two feet, or at least three feet (915 mm) if a depth number is not specified.(d)A basement floor that is below grade on all sides shall be elevated at least two feet above the design flood elevation.
Full Breakdown
Austin adopted its flood-resistant construction rules under Sec. 25-12-54 as a home-rule exercise of the flood-control authority the Texas Legislature grants cities in Tex. Water Code Secs. 315. The operative elevation numbers sit in Sec. 25-12-53(C)(1): the lowest floor must clear the design flood elevation by two feet, and a two-foot freeboard applies wherever an elevation requirement is specified, unless Title 25 (Land Development) sets a different figure. Basement floors below grade on all sides get the same two-foot minimum over the design flood elevation.
In AO Zone shallow-flooding areas, the lowest floor must sit above the highest adjacent grade by the FIRM-listed depth number plus two feet, or at least three feet if no depth number is shown. Flood hazard areas are established in Sec. 25-12-53(B) by incorporating the FEMA Flood Insurance Studies and FIRMs for Travis County (Jan. 6, 2016), Williamson County (Dec. 20, 2019) and Hays County (Jan. 17, 2025), plus the city's own 100-year and 25-year floodplains, recalculated using Atlas 14 rainfall data where that remapping has been adopted.
Every elevation must be documented on FEMA Elevation Certificate 086-0-33, sealed by a registered professional engineer, surveyor, or architect, and submitted to the Floodplain Administrator; the building official reviews every permit application to confirm whether the site falls inside a flood hazard area before construction can proceed. These standards apply to subdivision of land, utility installation, manufactured home and RV placement, new construction, and substantial improvement or restoration of substantially damaged buildings alike (Sec. 25-12-54(C)(1)).
Violations & Fines
A structure built without meeting the two-foot freeboard or without a certified Elevation Certificate on file cannot clear building permit review by the Floodplain Administrator or building official. Nonconforming structures that predate the current flood standards may continue, but Sec. 25-12-54(C)(4) bars any change that increases the nonconformity, requires full compliance before a substantial improvement is made, and strips grandfathered status if the nonconforming use is discontinued for 90 days or if the structure is destroyed to 50 percent or more of its market value, in which case rebuilding must meet current elevation rules.
Frequently Asked Questions
How high above flood level must a new Austin home be built?
What is the 'design flood elevation' Austin uses?
Do I need a certified elevation document to build in an Austin flood hazard area?
Can a basement be built in an Austin flood hazard area?
Sources & Official References
Other rules in Austin
Texas rules heatmap·Compare Austin to another location·View the Texas environmental rules overview
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Flood Elevation Requirements in Nearby Cities
How other cities in Travis County handle flood elevation requirements.