Ice and Water Shield Calculator

Total Eave Length (Linear Feet)

Required Eave Coverage (Width in Ft) 3 Feet (1 Course) 6 Feet (2 Courses) 9 Feet (3 Courses)

Number of Valleys

Avg. Valley Length (Ft)

Standard Roll Length (Ft)

Waste Factor (%)

Estimated Requirements:

Total Linear Feet Needed: 0 ft

Total Rolls Required: 0

Note: Based on standard 36-inch (3ft) wide rolls.

function calculateShield() { var eaveLength = parseFloat(document.getElementById('eaveLength').value); var eaveWidth = parseFloat(document.getElementById('eaveWidth').value); var valleyCount = parseFloat(document.getElementById('valleyCount').value); var valleyLength = parseFloat(document.getElementById('valleyLength').value); var rollLength = parseFloat(document.getElementById('rollLength').value); var wasteFactor = parseFloat(document.getElementById('wasteFactor').value); if (isNaN(eaveLength) || isNaN(valleyCount) || isNaN(valleyLength) || isNaN(rollLength)) { alert("Please enter valid numbers"); return; } // Calculation Logic // Eave coverage (if eave width is 6ft, we need 2x the length in 3ft wide rolls) var eaveRequirement = eaveLength * (eaveWidth / 3); // Valley coverage (standard 1 course per valley) var valleyRequirement = valleyCount * valleyLength; var totalBase = eaveRequirement + valleyRequirement; var totalWithWaste = totalBase * (1 + (wasteFactor / 100)); var rollsNeeded = Math.ceil(totalWithWaste / rollLength); document.getElementById('totalLinearFeet').innerText = totalWithWaste.toFixed(2); document.getElementById('totalRolls').innerText = rollsNeeded; document.getElementById('shieldResult').style.display = 'block'; }

How Much Ice and Water Shield Do You Need?

Ice and water shield is a critical self-adhering waterproofing membrane designed to protect the most vulnerable areas of your roof from ice dams and wind-driven rain. Unlike standard felt underlayment, this material creates a watertight seal around nail penetrations.

The Calculation Formula

To calculate the number of rolls required, roofing professionals use the following logic:

Eave Coverage: Total length of eaves × (Required coverage width / 3 feet). Most building codes require the shield to extend from the eave edge to a point 24 inches inside the interior wall line. On a standard overhang, this often requires two 36-inch courses (6 feet total).
Valley Coverage: Total linear feet of all valleys. Valleys are typically centered with one 36-inch wide roll.
Total Linear Feet: Sum of Eave and Valley requirements + 10% waste for overlaps and cuts.
Total Rolls: Total Linear Feet ÷ Length of one roll (Standard rolls are usually 66 or 75 feet long).

Example Estimation

Suppose you have a house with the following dimensions:

Eave Length: 120 feet
Required Width: 6 feet (2 courses)
Valleys: 2 valleys at 20 feet each (40 feet total)
Roll Length: 66 feet

Step 1: Eave requirement = 120 ft × 2 = 240 linear feet.

Step 2: Valley requirement = 40 linear feet.

Step 3: Subtotal = 280 linear feet. With 10% waste (28 ft), the total is 308 linear feet.

Step 4: 308 / 66 = 4.66. You would need to purchase 5 rolls.

Why Precision Matters

Ice and water shield is significantly more expensive than synthetic or felt underlayment. Overestimating leads to wasted budget, while underestimating can halt a roofing project mid-day. Always check your local building codes, as northern climates (snow belts) often have stricter requirements for how high the shield must reach up the roof slope.