Ice and water shield: where the code calls for an ice barrier, and how far up it goes
Ice and water shield is a self-adhering membrane laid on the roof deck where ice can back water up under the shingles. Where the code's map shows ice forming along the eaves, it calls for an ice barrier from the lowest edge of the roof to at least 24 inches inside the outside wall line, and on roofs of 8:12 or steeper, at least 36 inches up the slope from the eave too (IRC R905.1.2).
Anthony Hicks30+ years in construction. Updated November 5, 2026.
Reading as
What it is
Ice and water shield is the common name for a self-adhering, polymer-modified bitumen sheet: a sticky-backed membrane rolled onto the roof deck under the shingles. It stands between the deck and water that backs up under the shingles. The code calls it an ice barrier.
Where the code calls for it
In areas where there has been a history of ice forming along the eaves and backing up water, as the local code’s climate table shows, the residential code calls for an ice barrier under shingle, metal shingle, roll roofing, slate and wood roofs (IRC R905.1.2):
| Rule | What the code says |
|---|---|
| What | Two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet in place of the usual underlayment |
| From | The lowest edges of every roof surface |
| To | At least 24 inches inside the exterior wall line of the building |
| Steep roofs | On 8:12 and steeper, also at least 36 inches up the slope from the eave |
| Not needed | Detached outbuildings with no heated or cooled space |
The 24 inches is measured inside the wall, so a roof with a wide overhang needs a wider strip: a 2 foot overhang plus 24 inches inside the wall is about 4 feet measured level, and more along a slope.
How wide a strip, worked out
- Find the overhang, measured level from the outside of the wall to the edge of the roof.
- Add 24 inches for the run inside the wall.
- Turn it into a length along the slope: multiply by the pitch’s slope factor (1.118 for 6:12, 1.202 for 8:12).
- On 8:12 and steeper, use at least 36 inches along the slope if that’s more.
A 6:12 roof with a 1 foot overhang: (1 + 2) × 1.118 = 3.4 feet up the slope from the edge. The roof pitch guide gives the slope factor for any pitch.
Other places it goes
A shingle maker’s instructions can call for it in other places too, such as valleys; the code’s valley rules are in the guide to roof valleys.
Common questions
Is ice and water shield required?
Where the local code shows a history of ice damming along the eaves, yes, at the eaves (IRC R905.1.2). Elsewhere it’s the roofer’s or shingle maker’s call.
How far up the roof does ice and water shield go?
From the eave to at least 24 inches inside the outside wall line, and on 8:12 and steeper roofs at least 36 inches up the slope (IRC R905.1.2).
Does ice and water shield go over the drip edge?
At the eaves, underlayment goes over the drip edge (IRC R905.2.8.5), and the ice barrier starts at the lowest edge of the roof. The drip edge guide covers the edges.
Is it on a roof estimate?
Yes, a line of its own, priced by the area it covers along the eaves.