Ice Barrier, Underlayment and Drip Edge Calculator

Enter the eave length, the overhang, the pitch and your roll sizes and get the courses and rolls of ice barrier along the eaves, the rolls of underlayment for the roof and the pieces of drip edge, each rounded up once, with the working shown for an example. The ice barrier distances are the model code's, shown in a table.

Estimates for planning, not professional advice. Read the full notice.

Eaves, roof and rolls

Feet and inches, like 12' 6"

Feet and inches, like 12' 6"

Inches, like 4 in

Find it with the roof area calculator.

Check your label.

Check your label.

Check your label.

Check your label.

Inches, like 4 in

Inches, like 4 in

Inches, like 4 in

Inches, like 4 in

Feet and inches, like 12' 6"

Inches, like 4 in

Example: a gable roof with an ice barrier at the eaves

3 ice barrier rolls

  • Band along the slope 3 ft 4 1/4 in
  • Courses of the roll 2
  • Underlayment rolls 4 underlayment rolls
  • Drip edge pieces 16 drip edge pieces

Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.

Shopping list

Example: a gable roof with an ice barrier at the eaves
ItemSizeBuy
Ice barrierice barrier rolls3
Underlaymentunderlayment rolls4
Drip edgedrip edge pieces16

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    Worked example: a gable roof with an ice barrier at the eaves

    Show the working
    1. Run: the overhang plus the inside-wall distance 1 ft + 24 in[1] = 3 ft
    2. Band along the slope: the run times the pitch multiplier 3 ft × 1.118 = 3 ft 4 1/4 in
    3. The band less one side lap (the first course shows the full roll width, each further course the width less the side lap) 3 ft 4 1/4 in − 6 in = 2 ft 10 1/4 in
    4. Courses: that over the roll width less the side lap, rounded up 2 ft 10 1/4 in ÷ 2 ft 6 in = 2 courses
    5. Rolls: the courses along the eave, cut from rolls with an end lap, rounded up once 2 courses × 84 ft = 3 ice barrier rolls

    Assumptions

    The figures behind the example. Sourced figures link to their source below; a default is a starting value to check against your label or supplier.

    Underlayment waste allowance 0%
    Default No waste is sourced. Check your label or supplier.
    Ice barrier side lap 6 in
    Default Check the roll's instructions.
    Ice barrier end lap 6 in
    Default Check the roll's instructions.
    Underlayment side lap 2 in[1]
    Default The 2021 IRC, Table R905.1.1(2), gives a 2 inch lap at 4:12 or greater; the roll's own instructions may differ.
    Underlayment end lap 4 in[1]
    Default The 2021 IRC, Table R905.1.1(2), gives end laps of 4 inches; the roll's own instructions may differ.
    Drip edge piece length 10 ft[2]
    Default Englert's info sheet lists 10 ft lengths; other makers may differ.
    Drip edge lap between pieces 2 in[1]
    Default The 2021 IRC, R905.2.8.5, gives a lap of not less than 2 inches.
    Ice barrier distances 24 in[1]
    The 2021 IRC, section R905.1.2, says an ice barrier extends to a point not less than 24 inches inside the exterior wall line, and on slopes of 8 in 12 or more also not less than 36 inches along the slope from the eave edge.

    Eave band by roof pitch

    The band along the slope and the courses it takes, by roof pitch, for the example overhang and roll width

    Roof pitchBand along the slopeCourses of the roll
    2/12 3 ft 1/2 in2
    4/12 3 ft 1 15/16 in2
    6/12 3 ft 4 1/4 in2
    7/12 3 ft 5 11/16 in2
    8/12 3 ft 7 1/4 in2
    9/12 3 ft 9 in2
    12/12 4 ft 2 15/16 in2

    Each row is worked out on its own. The band is the overhang plus the inside-wall distance, times the pitch multiplier; from the steeper pitch in the second table the along-the-slope minimum is also checked, and the larger band is used.

    What the 2021 IRC says about the ice barrier

    The distances of section R905.1.2 as the code gives them

    FigureValue in the code
    Inside the exterior wall line, at least 24 inThe 2021 IRC, section R905.1.2, says an ice barrier extends to a point not less than 24 inches inside the exterior wall line, and on slopes of 8 in 12 or more also not less than 36 inches along the slope from the eave edge.
    Slope from which the along-the-slope distance also applies 8 in 12The 2021 IRC, section R905.1.2, says an ice barrier extends to a point not less than 24 inches inside the exterior wall line, and on slopes of 8 in 12 or more also not less than 36 inches along the slope from the eave edge.
    Along the slope from the eave edge, at least 36 inThe 2021 IRC, section R905.1.2, says an ice barrier extends to a point not less than 24 inches inside the exterior wall line, and on slopes of 8 in 12 or more also not less than 36 inches along the slope from the eave edge.

    Source: [1]

    These are model-code figures, and the code your area has adopted may differ. The code applies where there has been a history of ice forming along the eaves, as the local code designates.

    The drip edge piece length the page starts from

    One maker's printed piece length for drip edge

    ProductPiece length in the maker's sheet
    Englert drip edge 10 ft

    Figures in the Piece length in the maker's sheet column are per Englert's published data, checked Nov 12, 2026.

    Product names are trademarks of their owners. HoneyDoMath is not affiliated with, sponsored by or endorsed by these makers. Figures come from each maker's published sheets and are shown for information only.

    Source: [2]

    The calculator starts from this length; enter the length of the drip edge you use.

    Questions

    How far up the roof does the ice barrier go?

    The 2021 IRC, section R905.1.2, gives a distance inside the exterior wall line and, on steeper slopes, a distance along the slope; the second table quotes both. Local codes and amendments differ; your building department decides.

    How many rolls of ice barrier does an eave need?

    Each course runs the length of the eave. The calculator counts the courses the band needs from the roll width less its side lap, cuts them from rolls with the end lap, and rounds up once; the example shows the working.

    Is this an ice and water shield calculator?

    It counts rolls of any ice barrier from the roll size you enter. Ice and Water Shield is a trademark of its owner, and nothing here is from or endorsed by that owner.

    Local codes and amendments differ; your building department decides.

    Sources (2)
    1. 2021 IRC, Chapter 9 Roof Assemblies, R905.1.2 Ice barriers, International Code Council, 2021 IRC. Code or government
      “…in areas where there has been a history of ice forming along the eaves … as designated in Table R301.2 … not less than 24 inches (610 mm) inside the exterior wall line … slope equal to or greater than 8 units vertical in 12 … not less than 36 inches (914 mm)…”
      “…underlayment shall be one layer applied in the following manner: underlayment shall be applied shingle fashion, parallel to and starting from the eave and lapped 2 inches, … End laps shall be 4 inches and shall be offset by 6 feet.”
      “…Adjacent segments of drip edge shall be overlapped not less than 2 inches (51 mm). … mechanically fastened to the roof deck at not more than 12 inches (305 mm)…”
      Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used
    2. Drip Edge System info sheet, Englert Inc., undated. Manufacturer data
      “Englert Drip Edge is available in 6” and 4” sizes and comes in 10’ lengths.”
      Per Englert's published data, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used

    These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.

    Sources

    • [1] International Code Council, 2021 IRC, Chapter 9 Roof Assemblies, R905.1.2 Ice barriers. Checked November 12, 2026. https://codes.iccsafe.org/content/IRC2021P2/chapter-9-roof-assemblies
    • [2] Englert, Drip Edge System info sheet. Checked November 12, 2026. https://www.englertinc.com/sites/default/files/drip-edge-info-sheet.pdf

    Made with HoneyDoMath.com. Estimates for planning; check product labels and local codes before you buy or build.