Money & Risk | Insurance and Flood

Texas Windstorm and Flood Rules for New Multiplexes

Two sets of rules shape insurance for a new duplex, triplex or fourplex in Texas. On the coast, wind cover from the Texas Windstorm Insurance Association needs a windstorm certificate from the Texas Department of Insurance, and that means inspections during construction. Anywhere a lot sits in a flood zone, local elevation rules and federal flood insurance rules apply, and Houston sets its own elevation rule in its code. This page covers both, with the forms, dates and code sections.

Where the Windstorm Rules Apply

Insurance Code 2210.003 lists the 14 "first tier coastal counties": Aransas, Brazoria, Calhoun, Cameron, Chambers, Galveston, Jefferson, Kenedy, Kleberg, Matagorda, Nueces, Refugio, San Patricio and Willacy. The Texas Department of Insurance (TDI) describes the area its windstorm program covers this way: "Properties in 14 coastal counties and in parts of Harris County east of Highway 146 are in a designated catastrophe area." See TDI's page on whether you need a windstorm inspection.

In that area, owners who cannot get wind and hail coverage from a private insurer can buy it from the Texas Windstorm Insurance Association (TWIA). Two of the covered cities in this guide, Corpus Christi (Nueces County) and Brownsville (Cameron County), sit in first tier coastal counties.

Why New Buildings Need a Certificate

Insurance Code 2210.258, in chapter 2210, ties TWIA coverage to the building code. A structure built in the catastrophe area after the law's start date must meet the building code in TWIA's plan of operation, and "the association may not insure a structure described by Subsection (a) until a certificate of compliance has been issued for the structure." The section carries an exception for some homes dropped by private insurers. For a new duplex or fourplex, plan on the certificate.

TWIA's certification page says: "As of June 1, 2020, all Certificates of Compliance are issued by the Texas Department of Insurance as part of its Windstorm Inspection Program." The certificate you need depends on when the inspections happened. A WPI-8 is issued for new and ongoing construction that a TDI inspector or an appointed Texas licensed professional engineer inspected during the work. A WPI-8-E covers completed work, inspected by a licensed engineer.

The Windstorm Steps for a New Multiplex

Sources: TDI inspection process, TWIA windstorm certification, Insurance Code chapter 2210.

TDI's inspection process page is direct about timing: "You must apply with TDI (complete the WPI-1) before beginning construction." TDI inspectors must inspect while the construction or repair is under way, and not before it starts or after it ends. The same page says "TDI inspectors do not charge an inspection fee." If you miss the inspections, the WPI-8-E route needs an engineer to certify finished work.

The 2024 Codes Since April 1, 2026

TDI's windstorm codes page announces: "TDI Adopts 2024 Building Codes," effective April 1, 2026. Those are the 2024 International Residential Code (IRC) and International Building Code (IBC). A city may use an older edition for its own permits, because Texas law sets the 2012 IRC and IBC as the minimum city codes. A coastal project can therefore face two editions: the city's for the building permit and TDI's 2024 edition for the windstorm certificate. Ask both offices before the design is final.

Which code applies also depends on the building type. Texas law treats one- and two-family homes, and townhouses of up to three stories with separate exits, as residential. A triplex or fourplex with stacked units or shared exits falls under the commercial code. The building codes page explains the line.

Flood Insurance and the 30-Day Wait

The Federal Emergency Management Agency (FEMA) runs the National Flood Insurance Program (NFIP). Its flood insurance page says: "Plan ahead as there is typically a 30-day waiting period for an NFIP policy to go into effect." Buy the policy more than 30 days before you need it, and before closing on a purchase if the lender needs proof of it.

The same page says: "Homes and businesses in high-risk flood areas with mortgages from government-backed lenders are required to have flood insurance." To find your lot's flood zone, use FEMA's Flood Map Service Center (msc.fema.gov) or ask your city. The zone letter on the map (A, AE, X and others) decides the insurance rules and, in Houston, the elevation rules.

Houston's Elevation Rule

Houston rewrote its floodplain rules in Chapter 19 with Ordinance No. 2018-258, adopted April 4, 2018 and in force since September 1, 2018. Sec. 19-2 defines the "minimum flood protection elevation" as "the 0.2 percent flood elevation, plus 2 feet." The 0.2 percent flood is the flood with a 1 in 500 chance in any year, the 500-year flood. Sec. 19-33 sets where it applies:

Source: Houston Code of Ordinances, Chapter 19, Sec. 19-33 and Sec. 19-2.

The rule covers "the lowest floor and all utilities," so utilities must sit at that height too; ask the City which equipment counts. On a small lot, raising every unit of a duplex or fourplex can change the stairs, the driveway slope and the building height. Houston's multi-unit residential sites have a 30-foot height limit, measured from average grade, so check the elevation and the height limit together. The Houston page has the full lot rules.

Adding a Unit to an Existing House in Houston

If you add a second unit to a lot that already has a house, Sec. 19-33 treats the flood zones differently. In the 1 percent zones (A, AE, AH and A99), the elevation rule names "new residential construction, additions and substantial improvements," so an attached addition must also meet the 0.2 percent flood elevation plus 2 feet. In the X Shaded zone, the rule names new residential construction. A detached garage apartment is new residential construction in either zone. Ask the City how it classifies your plan before you draw it, because the answer sets the floor height.

Fire Sprinklers and Building Type

Fire rules also follow the building type. Under Occupations Code 1301.551(i), "after January 1, 2009, a municipality may not enact an ordinance, bylaw, order, building code, or rule requiring the installation of a multipurpose residential fire protection sprinkler system or any other fire sprinkler protection system in a new or existing one- or two-family dwelling." The ban covers one- and two-family dwellings only. For townhouses and buildings of three or more units, sprinkler rules come from the building and fire codes your city has adopted, so ask the city before you price a triplex or fourplex.

Questions to Answer Before You Buy a Coastal or Flood-Zone Lot

• Is the lot in one of the 14 first tier coastal counties, or in Harris County east of Highway 146?
• If so, has Form WPI-1 been filed with TDI before any work starts, and who will do the inspections during construction?
• Which code edition will the city use for the permit, and does the design also meet TDI's 2024 windstorm codes?
• What FEMA flood zone is the lot in, and what is its 0.2 percent flood elevation?
• In Houston, does the raised floor still fit under the height limit for the lot's use?
• Is flood coverage in place more than 30 days before you need it?

State Housing Laws Leave Flood Rules to Cities

The 2025 housing laws keep local flood and drainage powers. SB 15, the small-lot law, says it does not affect city rules on "flooding, sewer facilities, or well water located on an individual residential lot," and it lets a covered city require all subdivisions or all small lots to fully mitigate stormwater runoff. SB 840, which opens commercial land to housing, lists stormwater rules among the powers cities keep under Local Government Code chapter 218. A project that meets the state limits can still need full drainage and elevation work.

Rebuilding After a Storm and Your Tax Value

Property tax has one storm rule that rental owners should know. Under Tax Code 23.231(h), in chapter 23, a replacement structure for one "rendered uninhabitable or unusable by a casualty or by wind or water damage" is not treated as a new improvement for the 20 percent circuit breaker cap, unless it is larger or has a higher-quality exterior. That cap covers non-homestead property valued at $5,320,000 or less in 2026 and expires December 31, 2026. The property tax page explains the cap.

Where to Go Next

Related on VanPlex: the Houston page, the building codes page and the Texas multiplex guide overview.

Frequently Asked Questions

Official sources (checked October 2026)