Ice and Water Shield Calculator
Calculate how many rolls of self-adhering ice and water shield membrane you need for eaves and valleys, plus total cost.
How this calculator works
Ice and water shield is a self-adhering rubberized membrane sold in 2-square (200 sq ft) rolls. This calculator multiplies the eave or valley run length by the code-required band width to get the area needing protection, then divides by 200 sq ft per roll and rounds up, since you can only buy whole rolls.
Formula: Rolls = (Eave/valley length ft × Band width ft) ÷ 200 sq ft per roll, rounded up.
Worked example
A 40 ft eave line with a 6 ft required band width (240 sq ft):
- Area: 40 × 6 = 240 sq ft
- Rolls: 240 ÷ 200 = 1.2 → rounds up to 2 rolls
- At $100/roll, that’s $200.00.
Coverage reference
| Eave/valley area | Rolls needed |
|---|---|
| 60 sq ft | 1 roll |
| 240 sq ft | 2 rolls |
| 960 sq ft | 5 rolls |
How to measure your eaves and valleys
Measure the total linear run of every eave edge (and separately, every valley) you need to protect, in feet. For the width figure, use whatever band width your local building code requires for that roof slope and climate zone — this is usually 3 ft to 6 ft — rather than guessing, since underestimating this dimension is the most common ice-dam callback.
Frequently asked questions
How much roof does one roll of ice and water shield cover?
A standard roll is 2 squares — 200 square feet of coverage, before accounting for the required overlap between courses. This calculator divides your eave or valley area by 200 sq ft and rounds up to the next whole roll, since suppliers only sell full rolls.
What do the length and width fields mean here?
Length is the total run of eave (or valley) you're protecting, and width is the band width your local code requires — typically 3 ft along eaves in most cold climates, but some jurisdictions or steep valleys call for 6 ft or wider bands. Check your local code before entering a width.
Why is there no waste toggle for this calculator?
Ice and water shield is priced and measured precisely against the code-required band width, and running short on this layer is a leak risk, not a cosmetic one — so this calculator gives you the straight coverage math rather than an arbitrary waste percentage. Round up your final order slightly if your eave line has a lot of dormers or valleys.
How far up the roof does ice and water shield need to extend?
Most cold-climate codes require the membrane to extend from the eave edge to at least 24 inches inside the exterior wall line, measured along the roof slope. On a low-slope roof or one with a long eave overhang, that can mean more than one course of membrane, which changes your effective width entered here.
Do valleys need the same membrane as eaves?
Yes — valleys are just as prone to ice damming and wind-driven water intrusion as eaves, and many roofers run a full width of ice and water shield down every valley regardless of climate zone. Calculate valley coverage separately from eave coverage since the run lengths and required widths often differ.
Can ice and water shield replace regular underlayment?
No — it's a supplemental waterproofing layer for vulnerable areas (eaves, valleys, roof penetrations, low-slope sections), not a whole-roof product. The rest of the roof still needs standard synthetic or felt underlayment, calculated separately.
Estimates only. Verify quantities with your supplier before purchasing.