![]() Same info here - this is the tutorial page for the AWC calculator. Or, to put it another way, from a plumb line dropped from the peak, measured horizontally to the inside of the side wall.Ībove image from here, right at the article end. ? Have you references you can link to?Īll my working life rafter span has been 1/2 the horizontal distance from one side wall to the other side wall. Quoting: DaveBellThe Maximum Horizontal Span is: Sheathe the top of that with 7/16 max, then 30 lb felt This is strictly just my opinion (based on my logic)ġ2/12 (45° pitch) is plenty for snow load (with a metal roof)Įven 4x4 beams crossed with 2圆s is plenty for a roof, and makes an attractive ceiling I don't know why the table and the calculator don't agree more closely. If we relate that to the table in chapter 8, the max horizontal span is the slope length, not 1/2 the cabin span length. 14-1, minus overhang = 12-1 each rafter.ġ1 ft. His cabin span of 16, 12/12, 2 overhang, provides slope of 14-1. I suspect you mean visible on top, why you want to go with standing seam type. This sounds right, use #30 felt, not the 15. It will basically be a hot roof since it won’t be vented unless I put in baffles. Quoting: AKfisherI was thinking a 1/2 plywood sheathing and then felt, then the concealed fastener roofing panels. However if the roof is not well insulated sometimes snow will melt a bit and then freeze as the temps get colder. I know there is a belief that with a 12/12 pitch and metal, the snow will slide off and not be piling up. ![]() Another reason to upsize the rafters when dealing with high snow loads. With a 2 foot eve overhang the rafter tail loads can be high enough to stress the rafter, especially with the birdsmouth notch out. Knowing the species to be used, grade etc will permit more accurate results. A weather barrier, tar paper or a tyvek like synthetic would be used o the sheathing and the metal on that. Metal can be installed on sheathing, no purlins needed, although I know some folks like them. Sheathing- osb or plywood- 7/16 is okay, but 5/8 gives more for the roof fasteners to bite into. But, will the roof be insulated in the rafters or in a flat ceiling? 2x8 do not have much room for insulation. 2x8 can work, depending on species, grade, etc. Here is a screenshot from the AWC calculator android app. What is the snow load? If you don't know that, what is the nearest town?Ģx8 at 12" would have to be SS Select for both species. Quoting: AKfisherWhat should my rafter spacing be if I plan on a 12/12 pitch and 2x8 common lumber?
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