A.Christopher DeBlois, a structural engineer with Palmer Engineering Co. in Tucker, Ga., responds: Rafters can be safely staggered across a ridge board in most situations. Section 802 of the CABO One & Two Family Dwelling Code, "Roof Framing," does not explicitly require alignment of rafters on opposite sides of a ridge board. There are certain advantages to aligning the rafters, however, and unless you have a compelling reason not to, I recommend that you line them up. Not only does it make framing ceilings and collar ties easier, the roof framing simply looks more professional when the rafters align. Having said that, in many cases staggering the rafters does not create excessive stresses in the ridge board.
To satisfy myself that the ridge board will not be overstressed, I analyzed a somewhat conservative scenario. I chose a gable roof at a 6:12 pitch with 2x10 rafters spanning 16 feet from exterior walls to a 2x12 ridge board, to carry design loads of 30 pounds per square foot (psf) live load, and 15 psf dead load. In this scenario the unbraced...
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