Ice & Water Shield Rolls Calculator
Estimate rolls of ice-and-water shield for the eaves and valleys from run length, coverage width and roll size.
How it works
Eave area = eave × course width · Valley area = valley × valley width · Total = (eave area + valley area) × (1 + waste%) · Rolls = ceil(total ÷ coverage per roll)
Ice-and-water shield is a self-adhering membrane laid at the eaves and in valleys to block leaks from ice dams and wind-driven rain. Codes in cold climates typically require it to extend at least 24 inches inside the exterior wall line, which usually means one or two 36-inch courses up from the eave. Multiply each run by the up-slope width it must cover, add the valley strips, allow for the side and end laps, then divide by the square footage a roll delivers.
Worked example
For 120 ft of eave covered 3 ft up-slope (360 sq ft) plus 24 ft of valley 3 ft wide (72 sq ft), the area is 432 sq ft. A 10% lap allowance makes it about 475 sq ft, so at 200 sq ft per roll you need 3 rolls.
Frequently asked questions
How far up the roof should ice-and-water shield go?
Most cold-climate codes require it to reach at least 24 inches past the interior face of the exterior wall. On roofs with wide overhangs or low slopes that can mean two or three courses of 36-inch membrane, so measure the required up-slope distance for your wall and overhang.
Do I put it in the valleys too?
Yes. Valleys concentrate water and are a prime leak point, so a full-width strip of ice-and-water shield down every valley is standard practice even in milder climates.
How big is one roll?
A typical roll is 36 inches wide by about 66.7 feet long, covering roughly 200 sq ft. Some brands sell 1.5- or 2-square rolls — set the coverage field to your product’s actual figure.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.