3/20/2024 0 Comments 4 x 6 rafter span tableI hope someone will chime in on this, and is there a program or a calculater that already has these calculations set up? For what it's worth, I own another house less than a half mile from my house where the snow load is 300lb. Pat 4圆's 24oc seems like it would be fine, and I imagine you are using doug fir, but I don't know what the calculations are. I cannot explain all this in detail because I do not know the words in English and to not have time spending several weeks explaining it.ĭo not do this before you can do it right. You will forther have to calculate the number of nails needed at the junctions and check that it is smaller that the allowed nomber of nails on that size and shape of surface. The bending resistance W is given by 1/6 x b x h x h when b is the breadth and h the height of the beam or rafter. I do not know how that reduction is done in your construction code. You may have to reduce the compression resistance because of buckling. With a simple triangular (or kingpost truss) truss there will be both compressive and bending forces in the rafters. (like standing on wet ice with splayed legs) That force has to be taken up by something, for excample a joist or a long bolt from side to side. That means that there will be a horizontal component pushing the lower ends outwards. Some thought from one who learned wooden truss design last year.Ī truss that consists of only rafters, not tied togeather by ceiling joists at the bottom will spread and collapse forcing the walls outwards. Sorry for all the questions, but I'm trying to get more of a grasp of this stuff. Or I was thinking of a 2圆 ceiling joist on each side of my 4圆 rafters (across the 12' span), then a 4圆 king post. If I was to use a 2圆 ceiling joist and a 2圆 collar tie beam above on every rafter, does this substantially increase my span strength? Using the WWPA chart for 80lb snow and 15lb live load (for my species) they show 11' 6" span for a 2x12 24" O.C., but do not list a roof pitch. I have a clear 12' span to cross for an open truck bay (12x26), that will be an extended part of my building, with a gable roof at 7 in 12" pitch. what would a 4圆's equivalent be in a 2x? Is it as strong as a 2x12? I've got specs from The WWPA Online Lumber Technical Guide with my snow loads. I'm new to construction engineering, and I'm trying to make sense of load and span calculations.
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