Usually required by code if you already have two layers.
Estimated Results
Estimated Actual Roof Area: 0 sq. ft. (approx. 0 "squares")
Estimated Total Cost Range: $0 – $0
*These are rough estimates based on national averages for materials and labor. Actual contractor bids will vary based on location, complexity, accessibility, and market rates.
function calculateRoofingEstimate() {
// 1. Get Inputs
var footprintStr = document.getElementById('houseFootprint').value;
var pitch = document.getElementById('roofPitch').value;
var material = document.getElementById('materialType').value;
var needsTearOff = document.getElementById('includeTearOff').checked;
// 2. Validate numeric input
var footprint = parseFloat(footprintStr);
if (isNaN(footprint) || footprint <= 0) {
alert("Please enter a valid positive number for the house footprint area.");
return;
}
// 3. Define Multipliers and Costs (Constants based on industry averages)
// Pitch Multipliers: Steep roofs have more surface area than their footprint and cost more labor.
var pitchMultiplier = 1.0;
var steepnessLaborFactor = 1.0;
switch(pitch) {
case 'low':
pitchMultiplier = 1.10;
steepnessLaborFactor = 1.0;
break;
case 'medium':
pitchMultiplier = 1.20;
steepnessLaborFactor = 1.1; // Slight increase for standard pitch
break;
case 'steep':
pitchMultiplier = 1.35;
steepnessLaborFactor = 1.4; // Significant increase for difficult/dangerous pitch
break;
default:
pitchMultiplier = 1.20;
steepnessLaborFactor = 1.1;
}
// Material Base Costs per sq ft (Installed average, excluding tear-off)
var materialCostPerSqFt = 0;
switch(material) {
case 'asphalt':
materialCostPerSqFt = 4.50;
break;
case 'architectural':
materialCostPerSqFt = 6.50;
break;
case 'metal':
materialCostPerSqFt = 12.00;
break;
case 'tile':
materialCostPerSqFt = 18.00;
break;
default:
materialCostPerSqFt = 4.50;
}
var tearOffCostPerSqFt = 1.75; // Average cost to remove and dispose one layer
// 4. Perform Calculations
// Calculate actual surface area accounting for slope and waste factor (~10%)
var actualRoofArea = footprint * pitchMultiplier * 1.10;
// Calculate base material and install cost adjusted for labor difficulty
var totalMaterialInstallCost = actualRoofArea * (materialCostPerSqFt * steepnessLaborFactor);
// Calculate tear-off if selected
var totalTearOffCost = 0;
if (needsTearOff) {
totalTearOffCost = actualRoofArea * tearOffCostPerSqFt;
}
var totalEstimateBase = totalMaterialInstallCost + totalTearOffCost;
// Create estimate range (+/- 15% for market fluctuation)
var lowEstimate = totalEstimateBase * 0.85;
var highEstimate = totalEstimateBase * 1.15;
var squares = actualRoofArea / 100;
// 5. Format and Display Results
function formatCurrency(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
document.getElementById('resultArea').innerText = Math.round(actualRoofArea).toLocaleString();
document.getElementById('resultSquares').innerText = squares.toFixed(1);
document.getElementById('resultCostLow').innerText = formatCurrency(lowEstimate);
document.getElementById('resultCostHigh').innerText = formatCurrency(highEstimate);
document.getElementById('roofResult').style.display = 'block';
}
Understanding Your Roof Replacement Cost Estimate
Budgeting for a new roof is a significant home improvement expense. While an exact quote requires an on-site inspection by a professional contractor, understanding the primary factors that drive roofing costs can help you plan effectively. This calculator uses industry averages to provide a realistic baseline.
Key Factors Influencing Roofing Prices
The final bid you receive from a roofer depends on several critical variables beyond just the size of your house.
1. Roof Area vs. Footprint and "Squares"
Your home's ground floor square footage is not the same as your roof's surface area. Roofs have overhangs (eaves) and slopes. A 1,500 sq. ft. house might actually have 2,000 sq. ft. of roof surface once the pitch is accounted for. In the roofing industry, surface area is often measured in "squares." One square equals 100 square feet of roof area.
2. The Impact of Roof Pitch (Steepness)
The slope of your roof significantly affects labor costs. A low-slope roof is easy to walk on, making installation faster and safer. A steep roof requires additional safety equipment, harnesses, and slower, more careful labor, increasing the price. Furthermore, steeper roofs geometrically have more surface area than flatter roofs on the same house footprint.
3. Material Selection
The material you choose is the largest variable in cost.
Asphalt Shingles: The most common and affordable option. Standard 3-tab shingles are the cheapest, while architectural shingles offer better durability and aesthetics for a slightly higher price.
Metal Roofing: Highly durable and long-lasting, but significantly more expensive upfront due to material costs and specialized installation requirements.
Tile or Slate: Premium materials that can last over a century but are heavy and expensive, often requiring structural reinforcement of the roof deck.
4. Tear-Off and Disposal
If your existing roof already has two layers of shingles, building codes generally require "tear-off"—the complete removal of old material down to the wood deck—before a new roof can be installed. This adds substantial labor and dumpster disposal fees to the project total.