View Full Version : roof calculation help please

Bob Riefer
07-29-2011, 3:45 PM
There are all sorts of online calculators, and I have a construction calculator.. But I also need to know the math behind the actual calculation.

I desire to know how to calculate the diagonal of a roof, and to be able to figure that out for any pitch.

Google just served up calculators, but not the math.

Thank you!

Bruce Pratt
07-29-2011, 4:18 PM
If you mean by "the diagonal", the length, it is the square root of (rise*rise + run*run); essentially solving for the length of the hypotenuse of a triangle using the Pythagorean Theorem a^2 + b^2 = c^2.

If you need to work from a pitch of the roof, then it involves some simple trigonometry. You will need to know the pitch (roof angle) and length of the base (run) or height (rise) of the roof. If you have the roof angle and height, then the diagonal = height/sin(angle), if you have the roof angle and the base length, then diagonal = base/cos(angle).

Bob Riefer
07-29-2011, 6:15 PM
Perfect thank you Bruce!