Typical Roof Pitches

Understanding Roof Pitch

• The numbers notated on the 1-12 through 60-12 roof pitch classifications refer to the number of rising inches (the first number) for every inch of roof length, or run (the second number.) For example, a 4-12 roof rises 4 inches for every 12 inches of roof run. The higher the first number, which ranges from 2 through 60, the steeper the slope. the second number is always "12" and refers to one foot, or 12 inches of measurment. (See ref 1, 2)

Roof Pitch Standards

• Most homes have a roof pitch in the range of 1/12 through 12/12, or 45 degrees. A 4/12 roof pitch is the standard for most home- and business-building, but the 3/12 pitch, or 14.04 degree, home is more commonplace in the southern regions of the United States. To give you an idea of the steepness factor of a 4/12 pitch roof, consider that any roof pitch over 5/12 is considered unwalkable.

Pitch Levels

• In the construction industry, roof pitches below 1/12 are flat, while those between 1/12 and 4/12 are considered low pitch. A pitch between 4/12 and 21/12 is considered steep, while the range between 21/12 and 60/12 is extremely steep, which is known in the industry as a Mansard roof.

Calculating Roof Pitch

• Calculating your home or building's roof pitch is a simple task if you have access to a ladder. You do not need to climb onto the roof, but you will need access to at least 12 inches of roof run. You will also need a tape measure and a 12-inch carpenter's level. Once you have access to the roof, hold out the level so that it is perpendicular to the ground and the far end touches any part of the roof. Check that the level's bubble is centered. Next, using your other hand, run the tape measure from the end of the level closest to you to the edge of the roof, making sure to keep the tape measure perpendicular to the level. The number on the tape measure, in inches, equals the first number of your roof pitch, which is followed by a slash and the number 12.