How to Determine Roof Pitch in New Construction

Determining the pitch of a roof is a perfect example of the practical application of the algebra concepts learned in high school. Pitch and slope mean the same thing. The slope of a line on a graph is defined as rise over run. Roof pitch is calculated by determining the number of inches the roof rises in the vertical direction over twelve inches of horizontal extension. Pitch is designated by a fraction such as 4/12, four inches of rise over a 12 inch run. A 7/12 roof pitch is much steeper than a 4/12 pitch.



Determining the pitch of a roof in new construction can be important for roof estimates. Steeper pitches involve more expensive roofing costs. The pitch of the roof is also significant if you want to install a skylight.

Things You'll Need

• 18- or 24-inch carpenter's level with inch markings stamped on its edge
• Pencil
• Tape measure
• Framing Square
• 6- or 7-foot stepladder

Instructions

1. Place the ladder underneath the attic access panel in the ceiling. Climb the ladder and remove the access panel.

2. Enter the attic, being sure to bring your tools with you.

3. Place the end of the framing square against the bottom edge of a roof rafter.

4. Place the level in front of the framing square at the 12-inch mark. Adjust the level until the bubble is centered between the two marks on the glass cylinder.

5. Slide the level up until it touches the edge of the roof rafter, making sure the bubble remains centered in the cylinder. The level needs to stay at the 12-inch mark of the framing square.

6. Read the inch marking on the level where it intersects with the framing square. This number is the top number of the rise over run fraction.

Tips & Warnings

• If your level does not have one-inch marks on its edge, use your pencil and tape measure to mark them prior to entering the attic.

• Be certain the stepladder is sturdy and in good condition.

• It is advisable to have a helper hold the stepladder as you climb into the attic.

References

• Roof Estimatimator: How to Determine Your Roof Pitch
• This Old House: Determining Roof Pitch