The international residential code book, or I should say North Carolina’s version of it, says, “The span of each rafter shall be measured along the horizontal projection of the rafter’.
What does that mean? If the building width is 30 feet, does that mean the span is 15 feet or is it the actual length of the rafter from the outside of the wall plate to the ridge board?
Thanks for your help!
Replies
Rafter spans are designed based on horizontal dimensions, as you suspected.
What does an actor know about politics?" [Ronald Regan, criticizing Ed Asner for opposing American foreign policy]
Rafter spans are designed based on horizontal dimensions
In case you feel a need to tilt at windmills, try and get two plans examiners to agree on "where" horizontally to measure--outside to outside of bearing wall; center to center (as it ought to be); or inside to inside . . .
(O, do I need a three-day weekend . . . )Occupational hazard of my occupation not being around (sorry Bubba)
Oh, believe me - I've been involved in plenty of debates like that.
To paraphrase a saying I once heard about economists:"If you took all the engineers in the world and laid them end to end, they wouldn't reach a conclusion"
all the engineers in the world and laid them end to end, they wouldn't reach a conclusion
That may be more true of economists than engineers (I'm not certain economists are supposed to reach conclusions). Usually the engineers reach too many conclusions, and will not single one out as "best" (or even "better") . . . Occupational hazard of my occupation not being around (sorry Bubba)
Maybe the guy I was listening to was talking about them reaching a UNANIMOUS conclusion.
That would be pretty much impossible with both engineers and economists.How can a president not be an actor?" [Ronald Regan, when asked "How could an actor become president?"]
My interpretation of this has always been the length of the unsupported section (span) of the beam from center ot the peak to the top plate measured horizontally, as opposed to a linear measurement.
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
In framing square terms, it's called the "run".
-- J.S.
Earlier today I ran across a drawing that showed this exactly, but I can't find it now.
Anyway here is what Paul Fisette says;
"Sizing rafters differs from sizing joists in 2 ways:
1) The span of a rafter is not based on the measurement along its length. Rather, the span is based on the rafter's "horizontal projection". This is the horizontal distance from the inside surface of the supporting wall to the inside surface of the ridge board. So consider a simple gable roof on a 24-foot wide ranch framed with 2x6 exterior walls and a 1 1/2 ridge: the span would be 11'5 3/4". "
http://www.awc.org/technical/spantables/tutorial.htm
PS, I see that there is a drawing at the very bottom of the page.