Roof Slope Conversion Factor

On blue prints architects engineers usually display the pitch of a roof in the format shown on the image where number 4 represents a rise and number 12 represents a length.

Roof slope conversion factor.

For instance the ever last roofing company distributes a chart to the general public. You could calculate the slope factor for every single roof pitch but as a public service many roofing companies provide slope factor charts. A 10 slope roof should not be confused with a 10 pitch roof as a 10 slope roof means that the roof rises by ten inches for every foot of run. The following table shows how the same common roof slopes can be expressed using rise in run ratios degrees and percentages.

The headache of using pythagoras and trigonometry can be spared by making use of these charts. It s just a little math. Here are the equations you may use to solve for the length of the slope and the rafter. Multiply the roof length by the gable wall length 40 24 960.

Also see our page quick reference. See below after the table for directions on how to convert any roof slope from one form to another even roof slopes not shown in the table. Charts list the slope factor for various pitches usually from 1 12 to 12 12. Two most common methods 4 12 or 4 12 are used for marking the pitch of a roof.

The roof pitch factor is also used to calculate the length of common rafters. This will give you the rise over run or pitch. For example if you measure 4 inches the pitch of your roof is 4 12. The slope of the roof provides the rise and the run to be plugged into the equation.

Multiply this amount by the slope factor 960 1 1180 1073 28. Degrees to roof pitch rise in run to see a table. A roof pitch of 4 in 12 4 12 has a rise of 4 and a run of 12. Usually they come in the form of a roof pitch diagram chart but other times it will be presented to you in a conversion format.

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 this formula is from the pythagorean theorem. In essence a roof pitch chart is provided as a rough guide usually by a roofing company to help you see what the average roof pitches tend to be. In that case the multiplier is multiplied by the run of the rafter the horizontal distance that will be covered by the rafter.

The area of this roof 1073 3 sq. Use the following formula which also describes a right triangle. The combination of two numbers are used to display or show the roof pitch. Simply locate a roof rafter board place the end of the level against the bottom edge and measure from the 12 inch mark vertically to the bottom edge of the rafter.

You can also calculate roof pitch even without using a roof slope calculator.