I found a copy of the ASCE section 7 (or whatever it is called as referenced in the code) for calculating the snow load. I just went through this for my ongoing design of my cabin. I've always understood the span to be measured horizontally between points of bearing, not bracing. I do think the span reduction you took is incorrect if I'm understanding right. I'd rather reduce spans than reduce loads and strength. Might someone over the life of the structure install a porch roof? on the lee side? What's around the building? Go carefully when reducing loads. Over the life of the structure, at some point, might the load stick up there? I've seen vertical ice. How in the world? Well, thought I, it happens. He had 3' of consolidated ice and snow on it and an ice dam going on. We had built a 12/12 metal clad roof with 2x12's 12" on center. I quit trying to reduce the ground load after I got a phone call from Terry Peak in the Black Hills. The local Nautilus plant had a roof collapse, that broke the gas line, which then caught fire. In that snow storm we had several collapses. My home has exceeded design wind and snow loads as have several I have built, it's a best guess remember, that door swings both ways. Yup, it's a best guess based on past experience. Design is for resisting a maximum load that might occur at any time in the service life of the building. I'd never seen anything like it in the Sierras!Īnyway, I'm sure the engineering calcs assume stuff like this, but it was certainly counter to my intuition on snow build-up.ĭo think about it carefully before reducing the ground snow load. Even after we'd been in the cabin for two days with the fire roaring it still stuck to the roof, forming vertical snow waterfalls at the edge, hanging down to the mid point of our windows. And then the snow stuck to everything like glue for a two-week cold spell, including our roof and the trees. That was until a few weeks back when apparently it rained, then the temp dropped and it started to snow just as the rain froze. But for the last few year it seemed complete overkill as the roof never held more than a few inches of snow, and at most for a day or two (less if we had the fire going). We didn't get to reduce the ground snow load for reasons I can't quite remember (but that didn't bother me as our official snow load was probably low anyway and I didn't mind the extra margin). Have you already found the information you're looking for? Then check the roof shingle calculator that is dedicated to a slightly different topic of roofing.We've got a 12:12 standing seam metal roof. It can also be written down as 25% or 14°. Rafter² = rise² + run² = 1.5² + 6² = 2.25 + 36 = 38.25Ĭalculate the roof pitch as the proportion of rise and run:Īngle = arctan(pitch) = arctan(0.25) = 14°įinally, you can find the roof pitch in the form of x:12. Let's say it is equal to 1.5 m.Ĭalculate the rafter length, substituting these values into the following formula: Measure the run length – it is the horizontal distance between the roof ridge and the wall of the building. They have a pitch that can be as high as 21:12 (175%).īefore you start making proper calculations, you might want to open the angle conversion tool to convert between radians and angles.
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