Eave Ice-Barrier Membrane Courses and Rolls

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.

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.

The ice-barrier extent is stated in the published IRC R905.1.2; the slope-factor and roll relations are public roofing-takeoff arithmetic. The membrane standard is ASTM D1970.

Estimate. AHJ and licensed professional govern.

Field names used by the API: eave_length_ft, overhang_in, pitch_rise, roll_width_in, roll_len_ft, side_lap_in, slope_factor, coverage_in, courses, roll_lf, rolls

• Coverage extent coverage = (overhang + 24 in) measured up the slope: the slope factor sqrt(rise^2 + 144)/12 converts the horizontal run to the on-slope distanceIRC R905.1.2
• Courses the first roll covers one roll width; each later course nets (roll width - side lap), so courses = 1 + ceil((coverage - roll width) / (roll width - side lap)) once coverage exceeds one widthfirst principles
• Rolls roll_lf = courses x eave length; rolls = ceil(roll_lf / roll length); the roll dimensions are the product's stated sizefirst principles