Ice & Water Shield Calculator

Enter the dimensions of the roof, eaves, and valleys to calculate the amount of ice and water barrier needed for a roof.

By

Joe Sexton

Joe is the creator of Inch Calculator and has over 20 years of experience in engineering and construction. He holds several degrees and certifications.

Full bio

How to Calculate Ice Barrier Needed

Ice barrier membrane, sometimes called ice and water shield, is a self-adhesive membrane installed for protecting roof underlayment. It adds an additional barrier against ice and water that is forced into an asphalt shingle roof when ice dams form or during high winds and driving rain.

In cold climates, an ice barrier is often required by local codes. For example, states such as Minnesota require that an ice barrier membrane is installed extending 24″ beyond the inside of the exterior wall.^[1]

Most localities that require an ice barrier require it to cover from the edge of the eave to 24″ beyond the inside the exterior wall.

To calculate the ice and water barrier needed for a roof, you need to measure the roof pitch, overhang of the eaves, and thickness of the exterior wall.

Ice Barrier Formula

Once you have the roof pitch, eave overhang, wall thickness, you can use the following formula to calculate the coverage needed to protect 24″ beyond the exterior wall.

run = eave overhang + wall thickness + 24″
rise = run ÷ 12 × roof pitch
ice barrier coverage = run² + rise²

Once you calculate how far up the roof needs to be covered, you can calculate the total amount of ice and water barrier needed by multiplying the coverage in feet by the length of the eaves that need to be covered in feet.

total ice barrier required = ice barrier coverage × eave length

The calculator above applies all of these formulas to derive the amount of ice and water shield required for a roof.