I am looking at some tables of allowable roof loads for southern yellow pine: http://www.southernpine.com/app/uploads/AL_27-32L.pdf
Rafters are typically at an angle to horizontal. I'm wondering if the figures for "clear opening" in the tables refer to the length of a rafter or beam between supports, or to the horizontal "projection" of that opening.
In other words, if my rafters are at a 30-degree angle to horizontal, and are 16ft long between supports, is my clear opening 16ft, or is it 16ft times the cosine of 30 degrees, or a little under 14ft ?
Best Answer
Yes, the “clear opening” is the horizontal distance from support to support. (We often call this the clear span.)
In your case, the clear opening is about 14 feet. In fact, the clear span is the horizontal distance from FACE of support to FACE of support. It doesn’t matter the length of the member or if it’s a 4:12 pitch or a 12:12 pitch.