Note: Includes estimated 10% waste factor. Prices vary by region and contractor.
function calculateRoofCost() {
// 1. Get input values
var groundAreaInput = document.getElementById("groundArea").value;
var pitchMultiplier = parseFloat(document.getElementById("roofPitch").value);
var materialPricePerSqFt = parseFloat(document.getElementById("roofMaterial").value);
var includeTearOff = document.getElementById("tearOff").checked;
// 2. Validate Input
if (!groundAreaInput || isNaN(groundAreaInput) || groundAreaInput <= 0) {
alert("Please enter a valid ground area square footage.");
return;
}
var groundArea = parseFloat(groundAreaInput);
// 3. Logic Configuration
var wasteFactor = 1.10; // 10% waste for cuts and overlaps
var tearOffPricePerSqFt = 1.75; // Average cost to remove old shingles and dump fees
// 4. Calculate Actual Roof Surface Area
// Roof Area = Ground Area * Pitch Multiplier * Overhang/Waste Factor
var actualRoofArea = groundArea * pitchMultiplier;
var billableArea = actualRoofArea * wasteFactor;
// 5. Calculate Component Costs
var totalMaterialCost = billableArea * materialPricePerSqFt;
var totalTearOffCost = 0;
if (includeTearOff) {
// Tear off is usually calculated on the actual area + slight waste, but typically billed on total squares removed
totalTearOffCost = billableArea * tearOffPricePerSqFt;
}
var grandTotal = totalMaterialCost + totalTearOffCost;
// 6. Display Results
document.getElementById("displayArea").innerText = Math.round(billableArea).toLocaleString();
document.getElementById("materialCost").innerText = Math.round(totalMaterialCost).toLocaleString();
document.getElementById("tearOffCost").innerText = Math.round(totalTearOffCost).toLocaleString();
document.getElementById("totalCost").innerText = Math.round(grandTotal).toLocaleString();
// Show result box
document.getElementById("results").style.display = "block";
}
How to Estimate Roofing Costs in 2024
Replacing a roof is one of the most significant investments a homeowner will make. The cost of a new roof varies drastically based on the materials used, the complexity of the roof (pitch), and the size of the home. This guide explains the specific metrics used in our Roofing Cost Calculator to help you budget accurately.
Understanding the "Square"
While homeowners think in terms of square footage, roofing contractors measure projects in "squares." One square equals 100 square feet of roof surface. For example, if your roof surface area is 2,000 square feet, a roofer will quote you for 20 squares. Our calculator converts your ground footage into billable square footage automatically.
Key Cost Factors
Roof Pitch: The steeper the roof, the higher the cost. Steep roofs (above 8/12 pitch) require special safety equipment and take longer to install, increasing labor costs significantly. A flat roof has a multiplier of roughly 1.05, whereas a steep mansard roof may have a multiplier of 1.45 or higher.
Material Choice: Asphalt shingles are the most common and affordable option, typically costing between $4.50 and $7.00 per square foot installed. Premium materials like metal, clay tile, or slate can cost 3 to 4 times as much.
Tear-Off: If you have multiple layers of old roofing, or if the existing shingles are damaged, they must be removed. This adds labor and disposal fees (dumpsters), usually averaging $1.50 to $2.00 per square foot.
Waste Factor: Roofs are rarely perfect rectangles. Ridges, valleys, and dormers require cutting shingles, which creates waste. A standard estimate includes 10% to 15% extra material to account for this.
Average Roofing Material Costs (Installed)
Material Type
Cost Per Sq. Ft.
Lifespan
3-Tab Asphalt Shingles
$3.50 – $5.50
15-20 Years
Architectural Shingles
$5.00 – $8.00
25-30 Years
Standing Seam Metal
$9.00 – $14.00
50+ Years
Concrete/Clay Tile
$11.00 – $18.00
50+ Years
Slate
$15.00 – $30.00
100+ Years
Does Roof Pitch Affect Square Footage?
Yes. A common mistake when estimating roofing costs is assuming the roof area equals the home's square footage. Because roofs are sloped, the actual surface area is larger than the ground footprint. For example, a home with a 1,500 sq. ft. footprint and a medium slope (6/12 pitch) actually has a roof surface area of roughly 1,680 sq. ft. before adding waste factors.
When Should You Replace Your Roof?
Look for curling or buckling shingles, missing granules (bald spots), daylight showing through roof boards in the attic, or sagging. If your asphalt roof is over 20 years old, it is likely nearing the end of its serviceable life.