Determine and apply IRC R905.1.2 ice barrier requirements for a steep-slope reroof in a jurisdiction with a history of ice damming.

Steps

1. Confirm which IRC edition (and any local amendments) the AHJ has adopted, since ice barrier language and section numbering can shift between editions.
2. Verify the project is in a region 'where there has been a history of ice forming along the eaves causing a backup of water' — the trigger condition in R905.1.2, not just 'cold climate.'
3. Specify an ice barrier per R905.1.2: two cemented layers of underlayment, or one self-adhering polymer-modified bitumen sheet meeting ASTM D1970.
4. 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.
5. For roofs 8:12 or steeper, add the additional up-slope ice barrier coverage required by the adopted edition, measured along the roof slope from the eave edge.
6. Check for local amendments, since many northern jurisdictions extend the 24-inch minimum beyond the base code value.