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Ice and Water Shield Calculator

Updated How we build and test

Enter the length of your eaves and valleys to see how many rolls of ice and water shield to buy.

Both eaves added together.

The barrier must reach at least 24 in inside the exterior wall line.

Any other length you want covered.

ft

A 36 in × 66.7 ft roll covers 2 squares. Some rolls are 75 ft.

%

Rolls to buy

Enter the eave length.

How to use the ice and water shield calculator

  1. Add the length of every eave and enter the total. A simple gable roof has two.
  2. Choose one or two courses. Each course is one 36 in wide strip.
  3. Add the length of the valleys and anything else you want protected, such as the rakes or the area around a chimney or skylight.
  4. Check the roll length on the product you are buying.

Formulas

Length = eave length × courses + valleys + other
With overlaps = length × (1 + waste % ÷ 100)
Rolls = length with overlaps ÷ roll length, rounded up
Area = length × 3 ft

How many courses do I need?

Where the building code requires an ice barrier, it must run from the edge of the eave to a point at least 24 in inside the exterior wall line, measured level (IRC R905.1.2). Add the overhang, the wall thickness and 24 in, then adjust for the slope. With a 12 in overhang and a 6 in wall that is 42 in level, which is about 47 in up a 6 in 12 roof: more than one 36 in course, so two are needed. Short overhangs on steep roofs can sometimes pass with one.

Worked example: 80 ft of eaves and 30 ft of valleys

  1. Eaves, two courses: 80 × 2 = 160 ft.
  2. Valleys: 30 ft, for 190 ft in total.
  3. With 10% for end laps and waste: 190 × 1.10 = 209 ft.
  4. Rolls: 209 ÷ 66.7 = 3.1, so buy 4 rolls.

Questions

How much does a roll of ice and water shield cover?

The common roll is 36 in × 66.7 ft, which is 200 ft² or two roofing squares. Allow for a 6 in end lap where rolls meet and a 3.5 in side lap between courses.

Is ice and water shield required by code?

The IRC requires an ice barrier in areas with a history of ice forming along the eaves, as designated by the local jurisdiction. Many roofers install it at eaves and valleys everywhere because those are the places roofs leak first.

Can I cover the whole roof with it?

It is done on low-slope roofs and in severe climates, but a fully sealed deck cannot dry to the outside, so attic ventilation has to be right. Check the shingle and membrane manufacturers’ instructions first.

Sources

  1. 2021 International Residential Code, Chapter 9, Section R905.1.2 (Ice barriers), International Code Council. Used for: where the barrier must extend.

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