Formula Roof Pitch Multiplier

For example a 4 12 pitch roof that is 100 square feet.

Formula roof pitch multiplier. Where a is the rise of the roof b is the run of the roof and c is the rafter hypotenuse of the triangle with side lengths a and b. Measure the rise of your roof. Use the following formula which also describes a right triangle. Calculate the rafter length substituting these values into the following formula.

Take your area result and multiply it by the pitch multiplier or slope correction factor found in the table above to arrive at the roof s surface area. If the home measures 20 x 40 and has a 7 12 roof then to calculate the slope of the roof follow these steps. Next multiply the footprint of the roof by the multiplier below for your roof pitch to find the overall roof area. Rafter rise run this formula is from the pythagorean theorem.

The formula for the roof pitch multiplier comes from the famous pythagorean theorem. A roof pitch multiplier also called a roof pitch factor is a number that is multiplied by the area covered by a sloped roof to produce the area of the actual surface of the roof. Here are the equations you may use to solve for the length of the slope and the rafter. Now you re ready to price out the materials.

Step 1 multiply 20 and 40 which equals 800. Pitch rise run 1 5 6 25. For roof slopes expressed as x in 12 rise in run the roof pitch multiplier is determined by finding the square root of rise run 1. Image 1 12 to 12 12 roof pitch 7 12 pitch.

Roof pitch degree table. The pitch of this roof is 4 8 12. 800 multiplied by 1 16. Now divide the rise by the multiplier to get the pitch eg.

The calculator above can handle much of this math. Step 2 find the value of 7 12 from the roof slope multiplier table which is 1 16. Use our roof pitch calculator to find the pitch of your roof. 48 10 4 8.

If your roof is flat or has no more than a 3 in 12 pitch you can calculate its total square footage by simply multiplying the length by the width. Let s say it is equal to 1 5 m. 100 1 054 105 4ft2. You can also calculate roof pitch even without using a roof slope calculator.

Now solving for c in the equation above gives. Since pitch is the rise over a 12 inch run divide the run by 12 to get the multiplier in this case 120 12 10. Rafter rise run 1 5 6 2 25 36 38 25rafter 38 25 6 18 m.