Asphalt shingle roofs: underlayment per slope; ice barrier in regions with severe ice-dam history
2025 RCNYS §R905.2.7 Asphalt shingle underlayment + ice barrierDescription
Asphalt-shingle underlayment requirements (R905.1.1): for slopes 2:12 to <4:12, two layers of underlayment at every course; for slopes 4:12+, a single layer is permitted. In areas with a HISTORY of severe ice-dam-driven leaks (per Table R301.2), an ice barrier (two layers cemented or self-adhered polymer-modified bitumen sheet) must extend from the eave's edge to a point ≥ 24 in INSIDE the exterior wall line. For all of NY this is mandatory.
Why this exists
Ice dams form when warmed roof areas melt snow that re-freezes at cold eaves; water backs up under shingles and into the wall/ceiling cavity. The 24-in-inside-the-wall-line ice barrier is mandatory in NY and most northern states. Architects should specify it on the roof section + confirm with the roofer that it's actually installed; missing or wrong product is a common defect.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
iceBarrierExtent | min | 24 | in inside exterior wall | How far ice barrier extends past wall line |
Categories
Applies to
- Jurisdiction: New York State
Source
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Habitable space minimum ceiling height · IRC R305.1
- Wind design · IRC R301.2.1
- Seismic provisions · IRC R301.2.2
- Snow loads · IRC R301.2.3
- Floodplain construction · IRC R301.2.4
Last reviewed 2026-05-15.