How far up the roof does ice-and-water shield need to go, and where else should I run it?

Code Minimum (IRC R905.1.2 / IBC 1507.1.2): Extend 24 inches past the interior face of the exterior wall (measured horizontally). On a 4/12 pitch with 24" overhang, that’s ~54" up the slope from the eave edge. Steeper roofs/longer overhangs require more.

Where Else It’s Required (IRC R905.2.8.2):

1. Valleys: 36" wide centered (18" each side).
2. Penetrations: 12" up all sides of pipes, vents, chimneys, skylights.
3. Wall Intersections: 12" up sidewalls/headwalls (step-flash over it).
4. Transitions: Roof-to-wall, slope changes, dormers.

Best Practice (Do This):

• Eaves: Run two full courses (72") minimum. Cheap insurance against wind-driven rain and deep ice dams.
• Valleys: Run full 36" roll width (don't skimp on 18").
• Rakes/Gables: Run 12–18" up rake edges (wind-driven rain entry point).
• Low-Slope Areas (2/12–4/12): Cover entire deck.
• Climate Zone 5+ (Cold): Cover entire roof deck if heated attic or history of ice dams.

Critical Details:

• Lap shingles over membrane at eaves (membrane on deck, drip edge on top).
• At walls: Membrane first, then step flashing shingle-fashion over membrane.
• Use ASTM D1970 rated product (self-adhered polymer-modified bitumen).
• Prime OSB/plywood in cold weather (<40°F) or dusty decks.

Don't: Staple it, nail through it (except cap nails at top edge if mfr allows), or leave wrinkles/bubbles.

If roof slope <2/12, this does not apply—use low-slope membrane systems per R905.11.

Ice-and-water shield (also called self-adhering underlayment) is required by the International Residential Code (IRC) to protect against ice dams and wind-driven rain in vulnerable areas. Here’s the practical, code-based guidance:

Minimum Required Coverage (IRC R905.2.7.1):

• Eaves: Must extend at least 24 inches (2 ft) inside the exterior wall line of the building. (Note: In cold climates (IECC Climate Zones 5–8), many jurisdictions require 36–48 inches — check local amendments.)
• Valleys: Must run the full length of the valley, extending at least 12 inches on each side of the valley centerline.
• Around penetrations: Chimneys, skylights, vents, and dormers require ice-and-water shield extending at least 12 inches up and around the base (flashing integration point).
• Roof-to-wall intersections: (e.g., where a roof meets a sidewall) — extend shield at least 12 inches up the wall and 12 inches onto the roof deck (flashing behind siding, sealed to underlayment).
• Low-slope roofs (< 4:12 pitch): Often require full coverage — verify local code, as some jurisdictions mandate ice-and-water shield over the entire deck.

Best Practice Beyond Code:

• In high-snowfall areas, extend eave protection to 36–48 inches even if not required.
• Use it under all flashing details (chimneys, vents, skylights) as a secondary barrier — even if not code-minimum, it’s cheap insurance.
• Always lap shingles over the shield; never expose it to UV.

Critical: Ice-and-water shield is not a substitute for proper ventilation and insulation — ice dams start in the attic. Fix those first.

When to Call a Pro: If you’re unsure about local amendments, roof pitch, or complex intersections (e.g., crickets, multiple dormers), consult a licensed roofer or building inspector. Improper installation voids warranties and risks leaks.

Always verify with your local building department — amendments vary widely.