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Effective April 1, 2026, TDI adopted the 2024 International Building Code (IBC) and the 2024 International Residential Code (IRC) as the minimum construction standards for wind and hail hazard insurance policies through the Texas Windstorm Insurance Association.
There's one significant change in underlayment requirements when a new roof covering is installed on a property in the catastrophe area.
All sections of the catastrophe area are considered “high wind areas” and require underlayment for asphalt shingle and modified bitumen roof covers to follow one of the following methods shown in IRC Table R905.1.1(2).
- Two layers of mechanically fastened underlayment (No. 30 Asphalt-Felt or a synthetic underlayment conforming to ASTM D8257). Apply a strip of underlayment that is half the width of the full sheet parallel to and starting at the eaves, fastened sufficiently to hold in place. Starting at the eaves apply a full width sheet of underlayment, overlapping successive sheets half the width of a full sheet plus 2-inches. Distortions in the applied underlayment must not interfere with the ability of the roof covering to seal. End laps shall overlap at least 4-inches and shall be offset at least 6-feet.
- A minimum 4-inch-wide strip of self-adhering polymer modified bitumen underlayment conforming to ASTM D1970, installed per manufacturers installation requirements for the deck material, shall be applied over all joints in the roof deck. Then, apply a single layer of No.30 Asphalt-Felt or synthetic underlayment over the sealed roof deck as required by the shingle manufacturer, or the underlayment installation instructions.
- A single layer of self-adhering polymer modified bitumen underlayment conforming to ASTM D1970, installed per the underlayment and roof covering manufacturer's installation instructions, for the deck material, roof ventilation configuration and climate exposure of the roof covering.
For questions, contact TDI Engineering Services at 800-248-6032 option 5 or at Engineering@tdi.texas.gov.
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