Pitch Roof Calculator

Building Width (Span) (feet):
Building Length (feet):
Roof Pitch (Rise in inches per 12″ run):
Eave Overhang (feet):
Rake Overhang (feet):

function calculateRoof() { // Get input values var buildingWidth = parseFloat(document.getElementById("buildingWidth").value); var buildingLength = parseFloat(document.getElementById("buildingLength").value); var pitchRise = parseFloat(document.getElementById("pitchRise").value); var eaveOverhang = parseFloat(document.getElementById("eaveOverhang").value); var rakeOverhang = parseFloat(document.getElementById("rakeOverhang").value); // Validate inputs if (isNaN(buildingWidth) || isNaN(buildingLength) || isNaN(pitchRise) || isNaN(eaveOverhang) || isNaN(rakeOverhang) || buildingWidth <= 0 || buildingLength <= 0 || pitchRise <= 0) { document.getElementById("roofResults").innerHTML = "Please enter valid positive numbers for Building Width, Building Length, and Roof Pitch."; return; } if (eaveOverhang < 0 || rakeOverhang < 0) { document.getElementById("roofResults").innerHTML = "Eave Overhang and Rake Overhang cannot be negative."; return; } // Constants var PITCH_RUN_INCHES = 12; // Standard 12-inch run for pitch definition var PI = Math.PI; // Calculations var pitchRatio = pitchRise / PITCH_RUN_INCHES; // e.g., 6/12 = 0.5 var roofAngleRadians = Math.atan(pitchRatio); var roofAngleDegrees = roofAngleRadians * (180 / PI); var halfSpan = buildingWidth / 2; // Horizontal run from center to wall plate var totalRise = halfSpan * pitchRatio; // Vertical rise from wall plate to ridge // Rafter length from wall plate to ridge (hypotenuse of half-span and total rise) var rafterLengthNoOverhang = Math.sqrt(Math.pow(halfSpan, 2) + Math.pow(totalRise, 2)); // Sloped eave overhang length (horizontal overhang projected onto the slope) var slopedEaveOverhangLength = eaveOverhang / Math.cos(roofAngleRadians); // Total sloped rafter length including eave overhang var totalSlopedRafterLength = rafterLengthNoOverhang + slopedEaveOverhangLength; // Total roof length along the ridge, including rake overhangs (horizontal length) var totalRoofLengthWithRakes = buildingLength + (2 * rakeOverhang); // Area of one roof plane var areaOneRoofPlane = totalSlopedRafterLength * totalRoofLengthWithRakes; // Total roof surface area (both planes for a gable roof) var totalRoofSurfaceArea = 2 * areaOneRoofPlane; // Ridge Length (assuming simple gable roof, it's the building length) var ridgeLength = buildingLength; // Fascia Length: 2 along the eaves (totalRoofLengthWithRakes) + 2 along the rakes (totalSlopedRafterLength) var totalFasciaLength = (2 * totalRoofLengthWithRakes) + (2 * totalSlopedRafterLength); // Display results var resultsHtml = "

Roof Dimensions:

"; resultsHtml += "Roof Angle: " + roofAngleDegrees.toFixed(2) + " degrees"; resultsHtml += "Total Rise (from wall plate to ridge): " + totalRise.toFixed(2) + " feet"; resultsHtml += "Rafter Length (from wall plate to ridge, excluding overhang): " + rafterLengthNoOverhang.toFixed(2) + " feet"; resultsHtml += "Total Sloped Rafter Length (including eave overhang): " + totalSlopedRafterLength.toFixed(2) + " feet"; resultsHtml += "Total Roof Surface Area: " + totalRoofSurfaceArea.toFixed(2) + " square feet"; resultsHtml += "Ridge Length: " + ridgeLength.toFixed(2) + " feet"; resultsHtml += "Total Fascia Length: " + totalFasciaLength.toFixed(2) + " feet"; document.getElementById("roofResults").innerHTML = resultsHtml; }

Understanding Your Pitch Roof

A pitch roof, also known as a sloped roof, is a common roofing style characterized by its angled surfaces. The 'pitch' refers to the steepness of the roof, which is a crucial factor in its design, material selection, and overall performance. This calculator helps you determine key dimensions for your pitched roof project, from the angle of the slope to the total surface area.

What is Roof Pitch?

Roof pitch is typically expressed as a ratio of 'rise' over 'run'. The 'rise' is the vertical distance the roof climbs, and the 'run' is the horizontal distance it covers. For example, a 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal run. A higher rise number indicates a steeper roof.

Why is Roof Pitch Important?

Drainage: Steeper pitches shed water and snow more effectively, reducing the risk of leaks and water damage.
Material Selection: Certain roofing materials (like shingles) have minimum pitch requirements to ensure proper drainage. Low-slope roofs might require specialized membranes.
Attic Space: A steeper pitch can create more usable attic space or allow for vaulted ceilings.
Aesthetics: Roof pitch significantly influences the architectural style and appearance of a building.
Cost: Steeper roofs generally require more material and can be more challenging (and thus more expensive) to build and maintain.

How the Pitch Roof Calculator Works

This calculator uses fundamental trigonometry to determine various roof dimensions based on your inputs:

Building Width (Span): This is the horizontal distance across your building, from one exterior wall to the opposite. The calculator uses half of this (the 'run' for one side of the roof) in its calculations.
Building Length: The horizontal length of your building, which directly influences the length of your roof's ridge and overall surface area.
Roof Pitch (Rise in inches per 12″ run): Input the 'rise' value of your roof's pitch (e.g., '6' for a 6/12 pitch). This value, combined with the standard 12-inch run, determines the roof's angle.
Eave Overhang: The horizontal distance your roof extends beyond the wall at the eaves (the lower edge of the roof). This adds to the total rafter length and roof surface area.
Rake Overhang: The horizontal distance your roof extends beyond the wall at the gables (the triangular ends of the roof). This adds to the overall length of the roof planes.

Calculated Outputs Explained:

Roof Angle: The actual angle of your roof's slope in degrees. This is derived from the pitch ratio.
Total Rise (from wall plate to ridge): The vertical height from the top of your wall to the peak (ridge) of the roof.
Rafter Length (from wall plate to ridge, excluding overhang): The length of a single rafter from where it rests on the wall plate to the ridge board, not including any eave extension.
Total Sloped Rafter Length (including eave overhang): The full length of a rafter, from the outermost edge of the eave to the ridge. This is crucial for ordering lumber.
Total Roof Surface Area: The combined area of all sloped roof surfaces in square feet. This is essential for estimating roofing materials like shingles, underlayment, and sheathing.
Ridge Length: The linear length of the ridge board at the peak of your roof.
Total Fascia Length: The total linear feet of fascia board needed for both the eaves and the rakes of your roof.

Example Calculation:

Let's say you have a building that is 24 feet wide and 40 feet long. You want a 6/12 roof pitch, with a 1.5-foot eave overhang and a 0.5-foot rake overhang.

Building Width: 24 feet
Building Length: 40 feet
Roof Pitch (Rise): 6 inches
Eave Overhang: 1.5 feet
Rake Overhang: 0.5 feet

Using the calculator with these inputs, you would find:

Roof Angle: 26.57 degrees
Total Rise (from wall plate to ridge): 6.00 feet
Rafter Length (from wall plate to ridge, excluding overhang): 13.42 feet
Total Sloped Rafter Length (including eave overhang): 15.09 feet
Total Roof Surface Area: 1237.66 square feet
Ridge Length: 40.00 feet
Total Fascia Length: 112.19 feet

This information is vital for planning your roof construction, estimating material quantities, and ensuring structural integrity.