How to Measure Roof Pitch from a Distance

You will learn how to determine the pitch of a roof even if you can't get within 10 feet of the house.

Difficulty: Moderate

Instructions

Things You'll Need:

• Protractor
• Thread
• Needle (or small fishing weight)
• tape
• hollow tube (like a straw)
• Calculator (or use table in picture)

1. Imagine a line running along a rooftop and on past the edge until it was eye height from the ground. Now imagine your eye is staring straight up at that line so that your line of sight is parallel to the roof. The tilt of your head would be the angle of the roof (in case of illustration it is 27°).

2. 
    
   Parts of a protractor

   The hollow tube should be taped parallel to the zero line and run across the protractor's vertex. The thread should be able to rotate freely inside the protractor's vertex (tape it or tie it so it rotates relatively freely at that point). A weight should be attached to the loose end of the string, like a plumb bob.

3. Back away until you can see the rooftop (you can't see the top if you are too close) then slowly walk back toward the house until you can no longer see the top of the roof.

4. Hold the straw to your eye with the protractor facing down so that the dangling string's angle can be measured. The angle of the roof and the angle between the string and the 90° mark are now the same.

5. 
    
   Same as Roof Angle

   Hold the straw to your eye with the protractor facing down so that the dangling string's angle can be measured. The angle of the roof and the angle between the string and the 90° mark are now the same.

6. The tricky part is you can't read the angle of the string on the protractor while looking through the straw so you need to take your free hand and hold the string in place while looking at the roof.

7. 
    

   Once you are holding the string in place, on the protractor, you can read the angle off the protractor. Subtract the reading on the outer scale from 90° to get the angle of the roof.

8. If you want to know the “pitch” for a 12 foot run then you can use the guide below or simply type 12 tan Ø on your calculator. (Ø is the angle of the roof).
   
   Guide: 14° → 3/12, 19° → 4/12, 27° → 6/12, 30° → 7/12, 34° → 8/12, 37° → 9/12, 40° → 10/12, 45° - 12/12

Tips & Warnings

• You want the string to rotate freely from the vertex so use very thin string like sewing thread.
• Gutters can get in your "line of sight". Just estimate the line of sight by taking an extra step forward.