Loft joists can act as collar ties if fastened well to the walls. You really should have at least one collar tie roughly in the middle of the building. I guess if your beam is strong and the span is 20', and the pitch is 12/12, it's going to be OK. A ridge won't sag if the walls won't spred. Now your collar tie won't work unless it's down at the top of wall. I don't even use a ridge board, but I truss plate the opposite rafters together like a truss. It is used as a way to nail rafters at the peak. I know some people think a ridgeboard is doing something, but it's not. So it boils down to whether or not this is a true structural ridge or not. calculate a drop/sag at midpoint of 1.36 inches (no snow load). But that's with no snow or wind loading added.įYI, twin 2x10, 20 foot long. If we calculate using a snow load of zero, and just count the weight of all roof materials at 15 lbs PSF, a beam of three 20 foot long (unspliced) 2x12 DougFir #2 will pass the deflection and fiberstress in bending tests. The total beam span is 20 feet as you said there are no intermediate supports. I can do beam size calcs if I know the design snow load, lumber species and grade. I have seen a 10/12 roof loaded with 20 inches or so of snow on metal all because it sleeted first making a rough surface for the subsequent snow to pile upon. Other mortals such as myself either should build for the maximum possible snow load regardless of roof pitch or be certain our insurance (building, health and life) is paid up. A good engineer can calculate that using formulas developed for roof slope shedding snow. Even with a 12/12 pitch some snow capacity should be allowed for. However, even a twin or triple set of 2x12 may not be strong enough depending on the snow load. Splices are permitted but only when directly over a support like a post. Most glues have poor shear performance meaning the nails are carrying virtually all the load. The main problem with the proposal, IF this is meant to be a true load supporting Ridge Beam, is the splice.
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