Eave Ice-Barrier Membrane Courses and Rolls
The self-adhering ice-and-water membrane the eave actually needs: the up-slope coverage from the overhang and pitch (IRC R905.1.2 runs it 24 in inside the exterior wall line, measured on the slope), the courses when that exceeds one roll width, and the rolls. A deep overhang or a low pitch quietly pushes the coverage past a single 36 in course, so a one-roll-per-eave guess shorts the order. Required only where the AHJ has adopted it; valley and low-slope coverage is a separate add. A material takeoff, not a flashing plan.
Formula and source
slope_factor = sqrt(pitch_rise^2 + 144) / 12; coverage_in = (overhang_in + 24) x slope_factor; courses = coverage_in <= roll_width_in ? 1 : 1 + ceil((coverage_in - roll_width_in) / (roll_width_in - side_lap_in)); roll_lf = courses x eave_length_ft; rolls = ceil(roll_lf / roll_len_ft).
IRC R905.1.2 (the ice-barrier extent: from the eave to 24 in inside the exterior wall line) and ASTM D1970 (self-adhering polymer-modified membrane), by name; the coverage-and-roll relations are first-principles geometry.
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