All eaves that need an ice barrier, added up.
Measured level, from the wall face to the fascia.
24 in under the IRC. Raise it if your code asks for more.
One 36 in strip down each valley.
Around chimneys, skylights, walls, low slope spots.
Read it off your roll label (36 in wide).
The lap line printed on the membrane.
Rolls of ice and water shield
5rolls
2 courses along the eaves: the membrane has to reach 40.2 in up the roof on a 6/12 pitch.
- Width needed up the slope
- 40.2 in (3.35 ft)
- Courses at the eaves
- 2 (covers 68.5 in)
- Eave membrane
- 240 lin ft
- Valley membrane
- 30 lin ft
- Other areas
- 0.0 lin ft
- Total with 5% waste
- 284 lin ft
- Area covered
- 851 sq ft
Chart
Eave width by pitch and overhang
Inches of membrane needed up the slope to reach 24 inches inside the wall, and the number of 36 inch courses (3.5 inch side lap) in brackets.
| Pitch | 12 in overhang | 18 in overhang | 24 in overhang |
|---|---|---|---|
| 3/12 | 37.1 in (2) | 43.3 in (2) | 49.5 in (2) |
| 4/12 | 37.9 in (2) | 44.3 in (2) | 50.6 in (2) |
| 5/12 | 39.0 in (2) | 45.5 in (2) | 52.0 in (2) |
| 6/12 | 40.2 in (2) | 47.0 in (2) | 53.7 in (2) |
| 7/12 | 41.7 in (2) | 48.6 in (2) | 55.6 in (2) |
| 8/12 | 43.3 in (2) | 50.5 in (2) | 57.7 in (2) |
| 9/12 | 45.0 in (2) | 52.5 in (2) | 60.0 in (2) |
| 10/12 | 46.9 in (2) | 54.7 in (2) | 62.5 in (2) |
| 12/12 | 50.9 in (2) | 59.4 in (2) | 67.9 in (2) |
How it works
How the ice and water shield math works
Eaves. Add the overhang to the distance the barrier must reach inside the wall (24 inches under the IRC), then multiply by the slope factor for the pitch. That is the width the membrane has to cover along the roof. The first course covers 36 inches; every course after it adds 36 inches less the side lap. Eave length times courses is the linear footage.
Valleys. One 36 inch strip centered in each valley, so the valley length goes in at one course.
Everything else. Chimneys, skylights, sidewalls and low slope sections go in as square feet and are turned into linear feet of a 3 foot wide roll.
Rolls. The total, plus waste, is divided by the roll length less one end lap, and rounded up. Some codes go further than the IRC minimum (the 2018 IRC and some states also ask for 36 inches up the slope on 8/12 and steeper), so set the inside distance to what your building department enforces.
Questions
What roofers ask about this
How far up the roof does ice and water shield have to go?
Is ice and water shield required on every roof?
How many square feet does a roll of ice and water shield cover?
Does ice and water shield go over or under the drip edge?
How much should the courses overlap?
More free tools
Other roofing calculators
All free, no sign up. See every roofing calculator or all free tools.
- Roof pitch to degreesConvert any pitch to degrees and back, with the slope factor, hip and valley factor and a full chart.
- Roofing labor cost per squareWhat your crew costs you per square, and the labor price of a job with pitch, tear off and story adders.
- Drip edge calculatorPieces of drip edge for the eaves and rakes, with the code overlap, waste and the nails to fasten it.
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