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Ice and water shield is the one roofing material that still stops a leak after water has already passed the shingles, because it bonds to the deck and self-seals around every nail. Cold-climate codes generally require it from the eave edge up past the interior wall line, plus valleys, chimneys, skylights and low-slope tie-ins. Granulated modified-bitumen membranes give footing under shingles, smooth film-faced membranes let metal panels move, butyl adhesives stay flexible in cold and tolerate heat under metal. This guide covers membrane types, required locations, lap and drip-edge details, exposure limits, and why insulation and ventilation are the real cure for ice dams.
The best ice and water shield for most asphalt shingle roofs is a granulated, self-adhered polymer-modified bitumen membrane labelled ASTM D1970 — the category that includes Grace Ice & Water Shield, GAF WeatherWatch, Owens Corning WeatherLock G and CertainTeed WinterGuard. Under metal or tile, pick a high-temperature grade (smooth or film-faced, often butyl-based) instead.
Ice and water shield is a self-adhering membrane that seals around fasteners and sticks directly to the deck. It goes at the eaves in any climate that freezes, in every valley, and around every penetration — the places where water is most likely to back up.
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| Roof covering | Best membrane type | What to check on the roll |
|---|---|---|
| Asphalt shingles | Granulated modified bitumen | ASTM D1970, walkable surface, UV exposure days |
| Standing-seam or exposed-fastener metal | High-temperature smooth / film-faced | Temperature rating (often 240–260 °F class), slip resistance |
| Concrete or clay tile | High-temperature membrane | Temperature rating and the tile maker's underlayment list |
| Low-slope section under shingles (2:12 to 4:12) | Granulated or smooth, full coverage of the low section | Lap details in the shingle instructions |
| Cold re-roof in late autumn | Butyl-based or cold-weather grade | Minimum application temperature |
In areas with a history of ice dams, IRC R905.1.2 requires an ice barrier — at least two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet — from the lowest edge of the roof to at least 24 inches inside the exterior wall line of the building. Your local building department decides whether your area is in that zone. On a deep overhang or low pitch that usually means two 36 in courses at the eave.
Ice and water shield is an underlayment for pitched roofs, made to be covered by shingles, metal or tile. It is not a finished flat-roof membrane, and UV breaks down the adhesive once the exposure limit on the roll is passed. For a flat or near-flat roof use a membrane made for it — EPDM, TPO or a cap-sheet modified bitumen system.
For shingle roofs, a granulated self-adhered modified-bitumen membrane that meets ASTM D1970, such as Grace Ice & Water Shield, GAF WeatherWatch, Owens Corning WeatherLock G or CertainTeed WinterGuard. Under metal or tile choose a high-temperature grade. Match the membrane to the shingle maker's system if you want their enhanced warranty.
Where the local code calls for an ice barrier (IRC R905.1.2), it runs from the eave edge to at least 24 inches inside the exterior wall line — usually two courses of 36-inch membrane. Valleys, around chimneys, skylights, and any low-slope section should also get it regardless of climate.
Granulated surfaces give better footing and hold up to short-term sun exposure, which makes them the usual pick under shingles. Smooth-surface membranes lie flatter and are preferred under metal panels where the panel needs to slide.
Not as the finished roof. It is an underlayment for pitched roofs and must be covered within its UV exposure limit. Flat roofs need a membrane made for them, such as EPDM, TPO or a modified bitumen cap sheet.
Only for the exposure window printed on the roll, typically a couple of weeks to a few months. Past that, UV degrades the adhesive. Plan to cover it in the same weather window when you can.
No. It handles the leak-prone zones — eaves, valleys, penetrations. The rest of the field still gets synthetic or felt underlayment. Using membrane on the whole roof can trap moisture unless the assembly is designed for it.
At the eave, the drip edge goes on the bare deck first and the ice barrier laps over it. At the rake the order reverses — underlayment first, drip edge over it.
Measure eave length and multiply by the number of courses, then add valley lengths plus a couple of feet at each penetration. The ice and water shield calculator does that maths and adds a waste allowance for you.