Texas Windstorm Roofing Requirements

Applies to the 14 Texas Seacoast counties along the Gulf Coast, where windstorm-resistant construction is required for Texas Windstorm Insurance Association (TWIA) coverage.

Texas does not have a statewide building code, but the Texas Department of Insurance (TDI) administers Seacoast windstorm construction rules in 14 first-tier coastal counties plus a portion of Harris County (a second-tier carve-out east of Highway 146). Homeowners in these areas typically buy coverage through the Texas Windstorm Insurance Association (TWIA), and TWIA will not insure a structure that cannot show a Certificate of Compliance (Form WPI-8) for its roof and exterior envelope. The WPI-8 inspection is the practical enforcement mechanism for windstorm code in Texas.

TDI uses a two-tier system. The first-tier (catastrophe area) covers the 14 designated counties seaward of the intracoastal canal: design wind 140–150 mph (Vult, Risk Cat II). The second tier covers the inland portion of those counties plus the eastern portion of Harris County: design wind 130–140 mph. As of April 1, 2026, TDI requires construction in designated catastrophe areas to comply with the 2024 IRC and 2024 IBC (28 TAC §5.4008 amendment, adopted November 21, 2025). Construction permitted between September 1, 2020 and March 31, 2026 follows the 2018 IRC/IBC. Fastening requirements track IRC R905.2.6 high-wind provisions: 6 nails per shingle, 12-gauge minimum, full-round-head, hot-dipped galvanized or stainless. Self-adhered underlayment is required at eaves, valleys, and penetrations, with synthetic mechanical underlayment in the field.

This guide consolidates the TDI Seacoast and WPI-8 inspection requirements for residential asphalt shingle roofing, the Tier I and Tier II distinctions, the fastener and underlayment rules, and the documentation contractors must provide to obtain the WPI-8 certificate. It links into the roofing calculator with Texas Seacoast presets that adjust shingle rating and fastening defaults.

Texas Seacoast Tier I and Tier II Boundaries

TDI defines two windstorm tiers for the Texas Seacoast per 28 TAC §5.4008(b). Tier I (the "first tier" or catastrophe area) is the area seaward of the intracoastal canal across the 14 designated coastal counties — design wind speed 140 to 150 mph (Vult, Risk Category II). Tier II (the "second tier") is the inland portion of those counties plus the eastern portion of Harris County (east of Highway 146) — design wind 130 to 140 mph. Outside these areas, Texas has no state-administered windstorm code and most counties default to whatever IRC edition the local jurisdiction has adopted. The WPI-8 inspection and TWIA coverage requirements apply only inside the designated catastrophe area.

Shingle Class and Wind Rating

Tier I requires asphalt shingles meeting ASTM D7158 Class H (130+ mph) AND ASTM D3161 Class F (110 mph). Tier II requires Class G or H. The shingle must be installed strictly per the manufacturer's instructions for high-wind application — typically meaning 6 nails per shingle, sealed with manufacturer-applied or contractor-applied asphalt cement, and certified by the manufacturer for the specific wind exposure. Many manufacturers publish "Texas Seacoast" or "TDI Seacoast" approval letters that contractors keep in the WPI-8 documentation packet.

Fastener Schedule and Nail Pattern

TDI Seacoast asphalt shingle fastening follows the IRC R905.2.6 high-wind table: 6 nails per shingle in Tier I and Tier II, regardless of slope. Nails must be 12-gauge minimum, with a 3/8-inch full-round head, hot-dipped galvanized or stainless steel. They must penetrate ≥3/4 inch into the roof deck or fully through. Staples are not permitted. Nails are placed strictly along the manufacturer's nail line; high or low nailing voids the warranty and the WPI-8 inspection. The starter strip must be a manufacturer-listed starter (not cut from a 3-tab shingle) and is hand-sealed with asphalt cement at the eave.

Underlayment and Drip Edge

TDI Seacoast requires a self-adhered (peel-and-stick) underlayment at eaves (extending from the edge to a point 24 inches inside the exterior wall line, minimum), in valleys, and around all penetrations. The field can use a synthetic underlayment (ASTM D8257 or equivalent) mechanically fastened with cap nails at 6 inches on edge and 12 inches in field. Some Tier I counties require self-adhered underlayment across the full deck — Galveston County notably enforces this. Drip edge is required at all eaves and rakes, minimum 0.019-inch aluminum or 0.024-inch galvanized steel, lapped 2 inches at joints, fastened at 12 inches on center.

WPI-8 Inspection and Documentation

The WPI-8 inspection is performed by a TDI-appointed Qualified Inspector after the roof is dry-in but before the final shingle layer in Tier I, OR upon completion in Tier II at TDI's discretion. The contractor must provide: manufacturer NOA-equivalent letter for the shingle, manufacturer installation instructions, a TDI Form WPI-2 (application for Certificate of Compliance), and photographs of the deck nailing pattern, underlayment laps, and shingle nail placement. The final WPI-8 Certificate of Compliance is filed with TDI and becomes a condition of TWIA insurance. Re-roofs follow the same process; pre-WPI-8 homes that fail inspection are uninsurable through TWIA.