R905.6 Slate and Slate-Type Shingles
In areas where there has been a history of ice forming along the eaves causing a backup of water as designated in Table R301.2(1), an ice barrier that consists of at least two layers of underlayment cemented together or a self-adhering polymer modified bitumen sheet shall be used in lieu of normal underlayment and extend from the lowest edges of all roof surfaces to a point at least 24 inches (610 mm) inside the exterior wall line of the building.
|4:12 ≤ slope < 8:12||4|
|8:12 ≤ slope < 20:12||3|
|Slope ≤ 20:12||2|
For SI: 1 inch = 25.4 mm.