Step 1: find your flood zone
Look up your address on FEMA’s flood map or the Harris County flood tools, and check whether your home has flooded before. Your survey or elevation certificate shows the finished-floor height.
Step 2: understand the 50% rule
A substantial improvement is work costing 50% or more of the structure’s market value, not counting land. Substantial damage is the same test applied to repairs after a flood. Either one requires bringing the building into compliance, which can mean elevating it.
Step 3: design around it
- Keep the scope under the threshold when elevation isn’t practical
- Build additions at the required elevation even if the house stays lower
- Use flood-resistant materials below the flood line
- Ask your insurer about Increased Cost of Compliance coverage after a flood
Common questions
What is the 50% rule in Houston?
In a mapped floodplain, if improvement or repair costs reach 50% of the building’s market value, the home must meet current floodplain rules, including elevation.
How high must I elevate in Houston?
Houston’s floodplain ordinance requires substantial improvements in the 100- and 500-year floodplains to be elevated above the 500-year flood level. Your engineer confirms the exact height for your lot.
Does an addition count toward the 50% rule?
Yes. Additions count, and the addition itself must be built to current elevation requirements.
Sources
This guide is general information, not legal, tax or financial advice. Rules change; confirm details with the agency named in the sources or a licensed professional.