Short answer
Where ice dams are a risk, the model code calls for an ice barrier from the lowest roof edge to at least 24 inches inside the exterior wall line, measured horizontally. On most roofs with an overhang, one 36 inch roll does not reach that far: Fine Homebuilding works out about 47 inches up the slope on a 6 in 12 roof with a 12 inch overhang. Plan two rows at the eaves, plus valleys and penetrations. Detached unheated buildings are generally exempt; check your local code.
How far up the roof it must go
The rule in the International Residential Code (R905.1.2) is measured from the lowest edge of the roof to a point at least 24 inches inside the exterior wall line of the building. Because that 24 inches is measured horizontally, the overhang and the wall thickness push the line well up the slope (Fine Homebuilding).
With a 12 in overhang and a 2x6 wall
| Roof pitch | Distance up the slope | Rows of a 36 in roll |
|---|---|---|
| 6 in 12 | about 47 in | 2 |
| 8 in 12 | about 50-1/2 in | 2 |
| 12 in 12 | about 59-3/8 in | 2 |
Figures from Fine Homebuilding. Your overhang and wall may differ, so measure. In heavy snow years, water can back up higher than 36 inches; the same article blames many leaks on barriers that stopped short.
Where else it goes
- Valleys, where two roof planes send water into one line.
- Low slopes, where water moves slowly and wind can push it up under laps.
- Around chimneys, skylights and vents, under the flashing.
- Under roll roofing at the eaves in ice dam areas. GAF’s roll roofing instructions name its leak barriers for exactly this (GAF).
Options worth buying
-
01Grip
Granulated ice and water shield
Best for: eaves and valleys under shingles or roll roofing
- Surface
- granules
- Width
- usually 36 in
- Backing
- split release film
- A granule surface usually gives better footing than film.
- Split release backing makes long runs easier to align.
-
02Metal roofs
Smooth or film faced self-adhered underlayment
Best for: under metal roofing, or where a smooth surface is specified
- Surface
- film
- Heat rating
- check for metal roofs
- Polyglass makes Polystick P as a high temperature underlayment for metal and other roof coverings (Polyglass).
Laying it? The method matches peel-and-stick roofing: see how to install peel-and-stick roofing. For the rest of the deck, compare synthetic and felt.
Questions people ask
Where is ice and water shield required?
In areas where the local code says ice forming along the eaves has caused a backup of water, the IRC requires an ice barrier at the eaves, from the lowest edge to at least 24 inches inside the exterior wall line. Your local building department decides whether your area is one of them.
How many rows of ice and water shield do I need?
Measure it. Add the overhang, the wall thickness and 24 inches horizontally, then convert to a distance up the slope. Fine Homebuilding gets about 47 inches on a 6 in 12 roof, 50-1/2 inches on 8 in 12 and about 59 inches on 12 in 12, all with a 12 inch overhang and a 2x6 wall. That is two rows of a 36 inch roll.
Can ice and water shield be left exposed?
Only for the time the maker allows, which differs by product. Polyglass, for example, lists exposure limits for its Polystick underlayments. Cover it with roofing within that window.
Is ice and water shield the same as peel-and-stick roll roofing?
No. Ice and water shield is an underlayment made to be covered. Peel-and-stick roll roofing is a cap sheet with granules made to face the weather. Both are self-adhered modified bitumen.
Is it slippery?
It can be. TAMKO warns that moisture, frost or debris on its ice and rain underlayment reduce traction and make it slippery, and tells installers to use fall protection.
See ice and water shield on Amazon
Sources
Last reviewed October 12, 2026. Products and listings change; check the data sheet and wrapper before you buy, follow the maker’s instructions, and check your local building code.