Determine whether ice barrier (ice-and-water shield) underlayment is code-required for a given climate and roof geometry

Steps

1. Check the IRC's ice-barrier trigger, which applies in areas with a history of ice forming along eaves causing water backup, as identified in the jurisdiction's adopted climate/weather table — this is a local-history determination, not a fixed statewide rule, so confirm with the local building department.
2. If required, specify either two cemented layers of underlayment or a self-adhering polymer-modified bitumen sheet installed in place of standard underlayment.
3. Extend the ice barrier from the lowest edge of all roof surfaces to a point not less than 24 inches inside the exterior wall line of the building.
4. For steep roofs (historically 8:12 or greater), confirm current-edition treatment of the extended coverage requirement, since recent IRC cycles have revised/clarified this steep-roof provision — verify against the specific edition adopted rather than assuming an older edition's wording still applies.
5. Check for local amendments in cold-climate jurisdictions that extend ice barrier requirements beyond the base IRC language (e.g., additional coverage at valleys, dormers, or low-slope transitions).