Houston | Flood Rules

Houston Flood Rules: Chapter 19 Zones, Elevation, Permits and Floodways

Chapter 19 of the Houston code sets how high a building must sit in a flood zone, when a floodplain permit is needed, and what may be built in a floodway. The current chapter came from Ordinance No. 2018-258, adopted April 4, 2018 and effective September 1, 2018. Its rules apply "throughout the city." This page gives the numbers by flood zone, with the section for each. The Houston overview gives the short version.

The Flood Zones Chapter 19 Uses

The zones come from the flood insurance rate map, which the Federal Emergency Management Agency (FEMA) issues. Sec. 19-1 adopts that map and the flood study behind it as part of the chapter. Two terms appear in most of the rules. The base flood is "a flood having a one percent chance of being equaled or exceeded in any one year." The 0.2 percent flood has a 1 in 500 chance in any year. Sec. 42-24 of Chapter 42 calls the two areas the 100- and 500-year floodplains.

Chapter 19 uses two areas. The "special flood hazard area" is land with a 1 percent or greater chance of flooding in any given year. The "Houston special flood hazard area" is wider: Sec. 19-2 defines it as land with "a 0.2 percent or greater chance of flooding in any given year," which adds the X Shaded zone.

Source: Houston Code of Ordinances, Sec. 19-2 and Sec. 19-31, 19-33 and 19-52, Supplement 93 Update 1.

Sec. 19-1(e) says the maps are open for public inspection in the office of the city engineer, who is their official keeper. Copies may be on the City website, but "the maps in the office of the city engineer shall control." Where a boundary is unclear, Sec. 19-12 tells the city engineer to read the map "in favor of inclusion of the site in a Houston special flood hazard area." Under Sec. 19-4 the city engineer may also apply newer flood study data, and the more restrictive elevation then controls.

Sec. 19-1(c) adds a warning. The chapter does not "imply that lands outside the areas of special flood hazards or uses permitted within such areas will be free from flooding or flood damage."

The Elevation Rule

Sec. 19-2 defines the "minimum flood protection elevation" as "the 0.2 percent flood elevation, plus 2 feet." The 0.2 percent flood elevation is the height above mean sea level that floodwater has a 0.2 percent chance of reaching in any given year. Sec. 19-33(a) applies it in zones A1 to A30, AE, AH, A and A99: for "any addition to, and new construction and substantial improvement of, any residential structure," the "lowest floor and all utilities must be elevated to at least the minimum flood protection elevation." Sec. 19-33(b) applies the same height in the X Shaded zone to additions and new construction.

Two definitions decide what gets measured. The lowest floor is "the lowest floor of the lowest enclosed area (including basement)." An unfinished or flood-resistant enclosure used only for parking, building access or storage, outside a basement, is left out of that term. Utilities means "all building utilities," and the definition lists electrical, heating, ductwork, ventilating, plumbing and air-conditioning equipment. Pool equipment, sewer cleanouts and landscape irrigation are excluded.

Sec. 19-32 sets general standards for all new construction in the Houston special flood hazard area. The building must be anchored against flotation, collapse and sideways movement, and built with materials that resist flood damage. Electrical, heating, ventilation, plumbing and air conditioning equipment must sit above the minimum flood protection elevation. A fully enclosed area below the lowest floor that is used only for parking, access or storage must let floodwater flow in and out. The section accepts a design certified by a registered architect or professional engineer, or at least two openings with a total net area of one square inch for every square foot of enclosed area.

For a multi-unit building the same height applies. Sec. 19-33 covers "any residential structure," and a non-residential structure may be elevated or floodproofed to the same level. Floodproofing means building or changing a structure to reduce or prevent flood damage.

Additions, Repairs and the 50 Percent Test

An addition is "any alteration to an existing structure that increases its footprint," which is the ground area the building covers. Sec. 19-33 sets a lower required height for small additions. An addition "no greater than 33% of the habitable area of the structure" may be built at one foot above base flood elevation, the height floodwater is calculated to reach in the 1 percent flood, in the A zones, and at the same elevation as the existing structure in the X Shaded zone.

Work on an existing building must meet the full rule when it is a substantial improvement: work whose cost "equals or exceeds 50 percent of the market value of the structure before the start of construction." The term includes a structure that has had substantial damage, which is damage that would cost 50 percent or more of the market value to repair. Market value "shall not include land value." Sec. 19-2 accepts the improvement value assigned by the county central appraisal district, a FEMA-approved estimating method, or an appraisal by a licensed appraiser.

Two limits narrow the test. Sec. 19-31 says substantial improvements and substantial damage "are regulated only in the special flood hazard area," the 1 percent land, so the test does not apply in the X Shaded zone. Work that only corrects cited health, sanitary or safety code violations is left out of the term, and so is an alteration of a historic structure that keeps its historic status.

The Floodplain Development Permit

Sec. 19-16 requires a floodplain development permit "in addition to any other permit that may be required for any development activity in a Houston special flood hazard area." Development is a broad word in Chapter 19. It means "any man-made change to improved or unimproved real estate," including buildings, filling, grading, paving and excavation. Sec. 19-11 makes the other permits depend on it: no building permit is issued and no plat is approved until the applicant shows compliance with the chapter, a variance, or a floodplain development permit.

Sec. 19-17 lists what the application must show, drawn to scale: the existing ground and the proposed changes, existing and proposed structures, the elevation of the lowest floor of every proposed structure, and the 0.2 percent flood elevations from the current flood study. The permit expires if development has not started within 18 months, and in any case when the project is complete or after five years. The permit holder must submit an elevation certificate, a signed statement from a licensed engineer or surveyor on the FEMA form, "before the framing of a structure has started." No permit is issued on a property with an existing floodplain violation unless the work will correct it.

Source: City of Houston, City Fee Schedule, "Flood plain" rows under the HPW (Houston Public Works) department, read October 8, 2026. The schedule says fees may be subject to an administrative fee under Code Section 1-14.

Conveyance, in the fee names, is the flow of floodwater across the land. Sec. 19-2 defines it as flow during the base flood "with a velocity that is greater than one foot per second or a depth that is greater than one foot." The schedule does not say which row the City applies to a site of three to eight homes, so confirm the category with Houston Public Works when you budget.

Fill and Lost Storage

Fill is "any material that is placed in an area and increases the elevation of that area or displaces water volume." Sec. 19-34 limits it. In areas the city engineer has found to have no conveyance capacity, development "shall not, at any time, diminish the storage volume within a Houston special flood hazard area." The applicant must show one of four things: the lost storage is replaced on the site "such that there is no net fill"; it is replaced off the site under City rules; the fill that comes with an elevated foundation is small enough that the City requires no mitigation; or, in the 0.2 percent floodplain, the fill does not block the 100-year overland sheet flow in the watershed, which is floodwater moving across the ground in a thin layer.

Where floodwater does flow across the land, or the city engineer has made no finding, the project may neither change the conveyance capacity nor reduce storage, and an engineer licensed in Texas must certify the analysis. The owner must maintain the storage and drainage works built to offset the project and recertify them to the city engineer each year (Sec. 19-34(c)).

Floodways

A floodway is "the channel of a river or other watercourse and the adjacent land areas that must be reserved in order to discharge the base flood." Sec. 19-43(a) sets a general ban: no floodplain development permit for fill, new construction, an addition or a substantial improvement in a floodway. A repair or renovation that is less than a substantial improvement is outside the ban. The section then lists the cases where the city engineer issues a permit:

• Existing structure. An addition to, or the replacement or substantial improvement of, a structure, when the bottom of its lowest horizontal structural member is at least three feet above the 0.2 percent flood level and the foundation is elevated floor construction (Sec. 19-43(c)).
• Vacant land. A new development, when the lowest horizontal structural member is at least two feet above the 0.2 percent flood level, the foundation is elevated floor construction, and an engineer shows the project provides floodway conveyance offset volume on the site or within one-quarter mile upstream in the same watershed (Sec. 19-43(d)).

Elevated floor construction is a foundation that holds the building above the natural ground on vertical and horizontal members. The lowest horizontal structural member is the lowest beam or other level support under the building. Floodway conveyance offset volume is earth dug out and removed to make up for the flow the new building blocks. Sec. 19-20(b) says "no variance may be granted for development on vacant land in a floodway," so the standards in subsection (d) are the only way to build there.

Plats in a Flood Zone

A plat is the recorded map that divides land into lots. Under Sec. 19-13, when any part of the property is in a Houston special flood hazard area, approval of the plat depends on a drainage plan that includes the 0.2 percent flood elevation data and is certified by a registered professional engineer. The Planning Commission "shall not approve a final plat until the city engineer has approved the drainage plan." Any storage or drainage feature required to offset the project must be shown on the final plat and the deed, and the duty to keep it stays with the land for each later owner. In Chapter 19 the word plat means a Class II or Class III subdivision plat or a street dedication plat.

Chapter 42 adds two points. A general plan must show all "the floodways and the 100- and 500-year floodplains" on the current FEMA map (Sec. 42-24). Floodplains and floodways do not count as compensating open space for a small-lot plat unless the Planning Commission approves an open space amenities plan (Sec. 42-183). The lot size and small lots page explains that open space.

Variances and Enforcement

A variance may be sought only because the requirement is "an exceptional hardship" (Sec. 19-20). The general appeals board decides it under Sec. 19-22 and must find the hardship, that "no feasible method or procedure is currently available to comply," and good and sufficient cause. It grants "only the minimum variance necessary." The owner must record the notice of the variance in the county real property records, with a signed statement that building below the flood level may raise flood insurance rates. The city engineer alone may grant one variance type: rebuilding on an existing foundation below the minimum flood protection elevation after fire, hail, wind or another event that is not flooding, with no larger footprint.

Sec. 19-91 gives the City five court actions, including injunctions, civil penalties and damages to pay for bringing a site into compliance. The city engineer may issue a stop work order, and a hearing on it must be held within three business days when requested. The city engineer may also file a certificate of non-compliance in the county deed records and may ask FEMA to deny flood insurance coverage for a property in violation. Sec. 19-92 makes a violation a misdemeanor, a lesser criminal offense, with a fine of "not less than $250.00 nor more than $2,000.00" for each day.

Flood insurance is a separate subject. See the insurance and flood page.

Where to Go Next

Related on VanPlex: the Houston overview, insurance and flood in Texas, and building codes from duplex to fourplex.

Frequently Asked Questions

Official sources (checked October 2026)