Ice and Water Shield: How Much Do I Need? Rolls by Eave and Pitch
Part of the project planner: Planning a roof replacement.
Ice and water shield is a self-adhering membrane that stops water backing up under shingles at the eaves, in valleys and around penetrations. For 80 ft of eaves on a 6/12 roof with a 12 inch overhang, the strip has to be about 3.91 ft wide along the slope, which is 313 ft². With valleys, penetrations and 10% extra, that comes to 2 rolls of 200 ft². The ice and water shield calculator does your own roof.
Width up the slope, by pitch
12 inch overhang, 6 inch wall, 24 inches inside the wall line, 80 ft of eaves, no penetrations:
| Pitch | Width up the slope | Eave area (ft²) | Rolls (10% extra) |
|---|---|---|---|
| 2/12 | 3.55 ft | 284 | 2 |
| 3/12 | 3.61 ft | 289 | 2 |
| 4/12 | 3.69 ft | 295 | 2 |
| 6/12 | 3.91 ft | 313 | 2 |
| 8/12 | 4.21 ft | 337 | 2 |
| 10/12 | 4.56 ft | 364 | 3 |
| 12/12 | 4.95 ft | 396 | 3 |
Rolls by length of eaves
6/12 roof, same overhang, no penetrations:
| Eave length | Membrane with 10% extra (ft²) | Rolls of 200 ft² |
|---|---|---|
| 40 ft | 172 | 1 |
| 60 ft | 258 | 2 |
| 80 ft | 344 | 2 |
| 120 ft | 517 | 3 |
| 160 ft | 689 | 4 |
Where it goes
- Eaves: from the drip edge to 24 inches (or the local rule) inside the warm wall line, measured along the slope.
- Valleys: a strip about 3 ft wide along the full length, under the valley metal.
- Penetrations: around chimneys, skylights and vent pipes.
- Low slopes: some codes and shingle makers require it over the whole roof if the pitch is shallow.
- Walls that meet roofs: along the wall, under the flashing.
How to install it
- Work on a clean, dry, smooth deck, within the temperature range on the roll (usually above 40°F).
- Start at the eave, cut the roll to length, peel back part of the film, and press it down, working up from the center to avoid wrinkles.
- Overlap courses by 3 inches (or as marked), and end laps by 6.
- Roll the membrane firmly with a hand roller, and lay it over the drip edge at the eaves (the drip edge goes over the underlayment at the rakes).
- Cover it soon: sunlight degrades it.
See also the roofing calculator and the roof replacement materials list. Estimates only: check your local code and the shingle maker's instructions.
Frequently asked questions
How much ice and water shield do I need?
For 80 ft of eaves on a 6/12 roof with a 12 inch overhang, about 366 ft² with 10% extra and two penetrations, which is 2 rolls of 200 ft². Valleys and more penetrations are extra.
How far up the roof should it go?
Most codes require it to extend at least 24 inches inside the exterior wall line, measured along the roof, in cold climates. Some areas ask for 36 inches. Check your local code.
How big is a roll?
Most rolls are 36 inches wide and about 67 feet long, which is 200 square feet.
Do valleys need it?
Usually: a strip about 3 ft wide along the valley. 30 ft of valley adds 90 ft².
Does a steeper roof need more?
Yes: the membrane has to reach farther up the slope. At 12/12 the strip is 4.95 ft wide against 3.91 ft at 6/12.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.