Roof Dimension Calculator

Roof Dimension Calculator

Calculated Roof Dimensions:

Roof Run:

Roof Rise:

Common Rafter Length:

Total Roof Surface Area:

function calculateRoofDimensions() { var buildingWidth = parseFloat(document.getElementById("buildingWidth").value); var buildingLength = parseFloat(document.getElementById("buildingLength").value); var roofPitchDegrees = parseFloat(document.getElementById("roofPitchDegrees").value); var eaveOverhang = parseFloat(document.getElementById("eaveOverhang").value); if (isNaN(buildingWidth) || isNaN(buildingLength) || isNaN(roofPitchDegrees) || isNaN(eaveOverhang) || buildingWidth <= 0 || buildingLength <= 0 || roofPitchDegrees = 90 || eaveOverhang < 0) { document.getElementById("roofResults").innerHTML = "

Calculated Roof Dimensions:

Please enter valid positive numbers for all fields. Roof pitch must be between 0 and 90 degrees."; return; } // Convert pitch from degrees to radians var roofPitchRadians = roofPitchDegrees * (Math.PI / 180); // 1. Calculate Roof Run (half of the building width) var roofRun = buildingWidth / 2; // 2. Calculate Roof Rise (vertical height from wall plate to ridge) var roofRise = roofRun * Math.tan(roofPitchRadians); // 3. Calculate Common Rafter Length // The main part of the rafter (from wall plate to ridge) var rafterLengthMain = roofRun / Math.cos(roofPitchRadians); // The part of the rafter for the horizontal eave overhang var overhangRafterLength = eaveOverhang / Math.cos(roofPitchRadians); // Total common rafter length including overhang var commonRafterLength = rafterLengthMain + overhangRafterLength; // 4. Calculate Total Roof Surface Area (for a simple gable roof, both sides) // Area of one side = (Common Rafter Length) * (Building Length) var totalRoofArea = 2 * commonRafterLength * buildingLength; document.getElementById("resultRun").innerHTML = "Roof Run: " + roofRun.toFixed(2) + " feet"; document.getElementById("resultRise").innerHTML = "Roof Rise: " + roofRise.toFixed(2) + " feet"; document.getElementById("resultRafterLength").innerHTML = "Common Rafter Length: " + commonRafterLength.toFixed(2) + " feet"; document.getElementById("resultTotalArea").innerHTML = "Total Roof Surface Area: " + totalRoofArea.toFixed(2) + " square feet"; } // Run calculation on page load with default values window.onload = calculateRoofDimensions;

Understanding Your Roof Dimensions

Accurately calculating roof dimensions is a crucial step for any construction or renovation project. Whether you're planning to build a new home, replace your roof, or simply estimate material costs, knowing the precise measurements of your roof components is essential. This calculator focuses on a common gable roof design, helping you determine key dimensions based on your building's specifications.

Key Terms Explained:

• Building Width: This is the horizontal distance across the building, from one exterior wall to the opposite exterior wall, perpendicular to the ridge line. For a gable roof, the roof's "run" is derived from this measurement.
• Building Length: This is the horizontal distance along the building, parallel to the ridge line. This measurement is critical for calculating the total roof surface area.
• Roof Pitch (Degrees): Roof pitch describes the steepness of your roof. It's typically expressed as a ratio (e.g., 4/12, meaning 4 inches of rise for every 12 inches of run) or, as used in this calculator, in degrees. A higher degree means a steeper roof.
• Eave Overhang (Horizontal): This is the horizontal distance that the roof extends beyond the exterior wall of the building. It provides protection for the walls and foundation from rain and sun.
• Roof Run: The horizontal distance from the exterior wall plate to the center of the ridge. For a symmetrical gable roof, this is exactly half of the building's width.
• Roof Rise: The vertical distance from the top of the wall plate to the peak (ridge) of the roof. This determines the height of your attic space.
• Common Rafter Length: This is the actual length of the structural member (rafter) that extends from the wall plate up to the ridge, including the portion that forms the eave overhang. This measurement is vital for ordering lumber.
• Total Roof Surface Area: The total square footage of the roof's exterior surface. This is a critical measurement for estimating roofing materials like shingles, underlayment, and sheathing.

How the Calculator Works:

This calculator uses basic trigonometry to determine the various roof dimensions. By inputting your building's width and length, the roof's pitch in degrees, and your desired eave overhang, it calculates:

1. Roof Run: Simply half of your building's width.
2. Roof Rise: Calculated using the tangent of the roof pitch angle multiplied by the run.
3. Common Rafter Length: Determined by dividing the run (plus the horizontal overhang) by the cosine of the roof pitch angle. This gives you the true diagonal length of the rafter.
4. Total Roof Surface Area: Calculated by multiplying the common rafter length by the building length, and then multiplying by two (for both sides of a gable roof).

Example Scenario:

Let's say you have a building that is 24 feet wide and 40 feet long. You want a roof with a 30-degree pitch and a 1.5-foot horizontal eave overhang.

• Building Width: 24 feet
• Building Length: 40 feet
• Roof Pitch: 30 degrees
• Eave Overhang: 1.5 feet

Using the calculator, you would find:

• Roof Run: 12.00 feet (24 / 2)
• Roof Rise: 6.93 feet (12 * tan(30°))
• Common Rafter Length: 15.59 feet (approx. 12 / cos(30°) + 1.5 / cos(30°))
• Total Roof Surface Area: 1247.20 square feet (2 * 15.59 * 40)

These precise measurements allow you to accurately cut rafters, estimate the amount of roofing material needed, and plan for the overall structure of your roof.