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Ice Dam Protection Calculator

Calculates ice and water shield underlayment needed for eave protection. Required in cold climates per IRC 2021 Section R905.2.8.1.

Combined length of all eaves requiring protection

IRC minimum: 3 ft in cold climates

Results

Slope Distance
--
ft per eave
Total Area
--
sq ft
Rolls Needed
--
225 sq ft/roll
With Overlap
--
sq ft total

This is a minimum per IRC code. Local codes may require additional coverage. Always check with your local building department.

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How to Use This Calculator

1. Enter the total eave length. Measure all eaves that need ice protection. On a gable roof, this is typically the front and back. On a hip roof, include all four sides.

2. Select the roof pitch. Steeper roofs require more material per linear foot of eave because the slope distance is longer than the horizontal distance.

3. Set the coverage distance. IRC code requires a minimum of 3 feet in cold climates. Many contractors extend to 6 feet or more for extra protection, especially on low-slope roofs.

4. Choose your climate zone. Cold climates require ice protection by code. Moderate climates may require it depending on local amendments.

How the Formula Works

The calculator converts the horizontal coverage distance to slope distance using the pitch correction factor, then calculates total area with overlap allowance.

Pitch_Factor = sqrt((Rise^2 + 144) / 144)

Slope_Distance = Coverage_Feet x Pitch_Factor

Base_Area = Eave_Length x Slope_Distance

Overlap = (Eave_Length / 36) x 2 sq ft

Total = Base_Area + Overlap

Rolls = ceil(Total / 225)

Frequently Asked Questions

How much ice and water shield do I need?
Multiply your total eave length by the required coverage distance (minimum 3 feet in cold climates per IRC code), then apply the pitch correction factor. One standard roll covers 225 square feet. A 120-foot eave at 6/12 pitch needs about 2 rolls for minimum code coverage.
Is ice and water shield required by code?
Yes, in cold climates. IRC 2021 Section R905.2.8.1 requires ice barrier underlayment extending at least 24 inches past the exterior wall line in areas with a history of ice dams. Check your local building code for specific requirements.
How far up the roof should ice and water shield go?
IRC code requires a minimum of 24 inches past the exterior wall line, which typically means 3 feet up the roof slope from the eave. In severe cold climates, many contractors extend to 6 feet or the first 2 courses.

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