function calculateRoofCost() {
// 1. Get Input Values
var footprint = document.getElementById("homeFootprint").value;
var pitchMultiplier = document.getElementById("roofPitch").value;
var materialCostPerSqFt = document.getElementById("roofMaterial").value;
var needsTearOff = document.getElementById("tearOff").checked;
// 2. Validate Input
if (footprint === "" || isNaN(footprint) || footprint <= 0) {
alert("Please enter a valid home footprint area in square feet.");
return;
}
// 3. Parse Numbers
var baseArea = parseFloat(footprint);
var multiplier = parseFloat(pitchMultiplier);
var materialCost = parseFloat(materialCostPerSqFt);
// 4. Determine Logic & Variables
// Tear off typically adds $1.50 – $2.00 per sq ft. We will use $1.75
var tearOffCost = needsTearOff ? 1.75 : 0;
// Calculate Actual Roof Surface Area (Geometry adjustment)
var roofSurfaceArea = baseArea * multiplier;
// Calculate Base Cost (Area * (Material + Labor + TearOff))
// Note: The material values in the select options include estimated installation labor
var costPerSqFt = materialCost + tearOffCost;
var subTotal = roofSurfaceArea * costPerSqFt;
// Add Waste Factor (Standard 10% for cuts and overlaps)
var wasteAmount = subTotal * 0.10;
var totalCost = subTotal + wasteAmount;
// 5. Display Results
document.getElementById("displayArea").innerHTML = Math.round(roofSurfaceArea).toLocaleString() + " sq ft";
document.getElementById("displayRate").innerHTML = "$" + costPerSqFt.toFixed(2) + " / sq ft";
document.getElementById("displayWaste").innerHTML = "$" + wasteAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("finalCost").innerHTML = "$" + totalCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Show result box
document.getElementById("resultBox").style.display = "block";
}
How to Estimate Roofing Replacement Costs
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 size of your home, the materials you choose, and the complexity of the job. Our Roofing Replacement Cost Estimator helps you calculate a realistic budget range by accounting for key variables that contractors use in their quotes.
Key Factors Affecting Your Roof Estimate
When calculating your roofing costs, consider these four primary drivers:
Roof Square Footage vs. Floor Area: Your roof is always larger than your home's footprint. The steeper the roof, the more surface area there is to cover. A steep "cathedral" style roof can have 40% more surface area than a flat roof on the same size house.
Pitch and Slope: Steeper roofs are more dangerous and difficult to walk on. Contractors charge a premium (often 20-40% more) for steep pitches because crews require safety harnessing and work slower.
Material Selection: Asphalt shingles are the most common and affordable option, usually costing between $4.50 and $6.50 per square foot installed. Premium materials like metal seams or slate can cost three to five times that amount.
Tear-Off Requirements: If you have multiple layers of old shingles, they must be removed before the new roof is installed. This labor-intensive process adds disposal fees and labor hours to your quote, typically adding $1.00 to $2.00 per square foot.
Understanding the "Waste Factor"
You might notice our calculator adds a 10% "Waste Factor" to the final total. In professional roofing, it is impossible to use 100% of the purchased material perfectly. Shingles must be cut to fit valleys, ridges, and edges. A standard 10% overage ensures you have enough material to complete the job without delays, and matches standard contractor estimating practices.
Average Material Costs per Square Foot (Installed)
To help you select the right option in the calculator above, here are current market averages for materials including installation labor:
3-Tab Asphalt: $3.50 – $5.00
Architectural Shingles: $5.00 – $8.00
Standing Seam Metal: $9.00 – $14.00
Clay or Concrete Tile: $12.00 – $20.00
Natural Slate: $18.00 – $30.00+
Note: These prices vary by region and season. Always get at least three quotes from licensed local contractors before signing a contract.