IRC Section R905.1.2 — Ice Barriers (adopted by Pennsylvania UCC)
"…an ice barrier shall be installed… The ice barrier shall consist of not fewer than two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet shall be used in place of normal underlayment and extend from the lowest edges of all roof surfaces to a point not less than 24 inches (610 mm) inside the exterior wall line of the building."
Steep Slope Addition (2015+ IRC):
"On roofs with slope equal to or greater than eight units vertical in 12 units horizontal (67-percent slope), the ice barrier shall also be applied not less than 36 inches (914 mm) measured along the roof slope from the eave edge of the building."
Key Interpretation Notes:
- "Inside the exterior wall line" means 24" measured from the interior drywall face — not from the exterior siding.
- The horizontal run (overhang + wall thickness + 24") must be converted to slope distance using the roof pitch.
- Standard IWS rolls are 36" (3 ft) wide. Practical coverage accounts for 2–3" overlap per manufacturer specs.
- The steep-slope provision (≥8:12) is additional — it does not replace the 24" interior wall requirement.
The Helping Company LLC | PA HIC# 149251 | HAAG Certified Inspector | IICRC Master Restoration Technician
thcexteriors.com | Reading, PA (Berks County)