When did Houston's 500-year floodplain rule take effect?

The Chapter 19 amendments were approved on April 4, 2018, and took effect on September 1, 2018.

Can I use fill to raise my ADU in Houston's floodplain?

Fill is limited. Houston extended its zero net fill requirement to the 500-year floodplain, so elevation usually comes from the foundation design, such as a raised slab or piers.

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How do Houston's floodplain rules affect an ADU?

Updated October 2026

As of October 2026, inside Houston city limits, new construction in the 500-year floodplain must have its lowest floor two feet above the 500-year flood elevation. The rule also covers substantial improvements, such as expanding a building's footprint by a third or more. Outside the floodplain, it does not apply.

When did Houston's floodplain rules change?

After Hurricane Harvey. City Council approved the Chapter 19 amendments on April 4, 2018, and they took effect September 1, 2018. The changes extended elevation rules from the 100-year floodplain to the larger 500-year floodplain.

What does the rule require?

New buildings and substantial improvements must be built two feet above the 500-year flood elevation.
An expansion of 33 percent or more of an existing footprint counts as a substantial improvement.
The city's zero net fill requirement was extended to the 500-year floodplain, which limits raising a lot with fill.

How does that shape an ADU?

On a mapped lot, a slab-on-grade cottage may need a raised slab or a pier-and-beam foundation to reach the required floor height. Because fill is restricted, simply bringing in dirt is usually not the answer. A garage apartment, where the living floor sits a story up, can meet the elevation more easily, though the garage below has its own rules.

Wood framing during construction: A wooden staircase in a wooden building

How do I know if my lot is in the floodplain?

Start with the FEMA Flood Map Service Center and the city's floodplain resources. Lot-level elevation comes from a survey or elevation certificate. We check this in the first lot review, before any design.

Does this apply in Bellaire, Pearland or Sugar Land?

It depends on the city. Houston's Chapter 19 applies inside Houston only. Each suburb runs its own floodplain program with its own freeboard and fill rules, and Harris County's rules apply in unincorporated areas. We check the rules for your city and your lot.

Check what your lot allows

Guides cover the general rules. For your address, we check restrictions, flood zone and city rules, then give you a written, itemized price.