Formula Roof Pitch Multiplier

Calculate the rafter length substituting these values into the following formula.

Formula roof pitch multiplier.

The calculator above can handle much of this math. 100 1 054 105 4ft2. 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. Pitch rise run 1 5 6 25.

You can also calculate roof pitch even without using a roof slope calculator. Rafter rise run this formula is from the pythagorean theorem. For example a 4 12 pitch roof that is 100 square feet. If the home measures 20 x 40 and has a 7 12 roof then to calculate the slope of the roof follow these steps.

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. 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. Step 3 multiply step 1 and step 2 i e. Here are the equations you may use to solve for the length of the slope and the rafter.

Let s say it is equal to 1 5 m. Measure the rise of your roof. 48 10 4 8. Use our roof pitch calculator to find the pitch of your roof.

Now divide the rise by the multiplier to get the pitch eg. The pitch of this roof is 4 8 12. Steep roofs measure your house at ground level then add in the roof s overhang for greater accuracy. Rafter rise run 1 5 6 2 25 36 38 25rafter 38 25 6 18 m.

Take the area of the roof s footprint say it s 5 000 square feet and multiply 5 000 by 1 118. The formula for the roof pitch multiplier comes from the famous pythagorean theorem. Now solving for c in the equation above gives. 800 multiplied by 1 16.

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. So the actual roof surface if it were laid down flat on the ground would be 1 118 times larger than the footprint of the roof. And for a roof with a slope of 6 12 that number 1 118 is your roof slope multiplier. Calculate the roof pitch as the proportion of rise and run.

Roof pitch degree table. Step 2 find the value of 7 12 from the roof slope multiplier table which is 1 16. Image 1 12 to 12 12 roof pitch 7 12 pitch. That gives you 5 590 square feet which is the actual area of the surface of the roof.

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.