4/10/2024 0 Comments Rafter spacing for metal roofingbeams, or for a metal roof on top of a standard truss layout. (for some reason the attachment comes out upside down so I posted it 2 ways.they're both the same image. truss & use extend to make them span entire length of roof. Now looking at my drawing, can I consider the span to begin where the new rafter is fastened to the existing top chord, rather than beginning at the wall? In other words, does nailing the rafter to the chord count as support? If so I can go out to an overall width of 12' for the lean to while not overloading the rafter. One goal is to make use of a lot of extra lumber I have, which includes 2圆's for the rafters, so I'd like to push it out to 12', on 24" centers.Īccording to the span charts, the limit of a 24" OC 2圆 is 10'9". It will eventually be enclosed but will not have ceiling or insulation. Length will be 54' long and as wide as I can make it in the space we have. The new roof will slide under the existing metal. To keep things simple, I'm planning on sliding the new rafters alongside the chords and resting them on the top row of banding. Our existing barn is a typical pole barn with 12" eaves and 2圆 top chords on the trusses. ![]() I'll have to figure that one out when I buy my roofing panels.We're planning a quick lean-to addition in a few weeks when I have a couple vacation days due. A panel of 24 gauge steel will accommodate a much greater purlijn spacing than a panel of 29 gauge steel. is adequate, but that really depends on the strength properties of the roof panel. So for my location I can put 4x8 rafters on 32" center.įor purlin spacing, I'm assuming 24" o.c. Using these loads for a 4x8 spanning 120 inches, my beam passes. So if I lessen the rafter spacing to 32" it might pass. Keeping all the other numbers the same, I changed Depth to 8 inches and clicked on ShowResult. The next thing I tried is going deeper, using a 4x8 rafter. If you are following along with this example using the calculator you find that it fails. Typical construction for residential roofing consists of rafters or trusses spaced 16 or 24 on center and at a pitch, or roof slope. Then click on Show Result to have the calculator determine if the beam passes or fails. You would pick what is available from your lumber supplier Species: I selected SPF #2 B+S, which covers the lowest structural grade of spruce, pine, and fir.Width of beam in inches: 4 because I'm using rough-sawn.Dead load: the weight of the roof borne by the rafter, 300 lbs.This tool will tell us if the desired rafter spacing is adequate for the rafter and load. Then click on the second link, which is for a Uniformly Loaded Simple Beam (the URL is at ). If you scroll down there you will find Don P's Calculators and you want to select the Beam and Column Calculators link. There are some really useful calculators at Forestry Forum at. So my rafter will be supporting a load of 30 s.f. You can calculate out what that is, but a convenient number to use is 10 lbs per s.f. The load includes the design weight for snow plus the weight of the roof itself. So each rafter is supporting an area of 3' * 10' or 30 s.f. That is the rafter spacing times the horizontal distance between the beams. The math part is figuring out the area and load each rafter will be supporting. I'm using big rafters widely spaced, shooting for 36" on center. The next part is pretty easy, and just requires some basic math. area for ground snow load, but applying wind and importance factors knocks it down to 50 psf. My location doesn't have a permit or inspector to worry about, so I'm just concerned about a roof that will withstand the elements, primarily snow. I'm considering the same question for a sawmill shed I plan on building. a 3-12 roof is the lowest slope you can go with metal roof panels. I used ABC panels to do my roof (Curtis Lumber carries them), and their installation guide would give you the spacing and sizing of the skip sheathing (purlins). They think they are going to get people building better houses but they end up getting the average guy to circumvent the code because it's so intimidating and potentially so expensive.Ī 50psf snow load 2圆 16" oc can span around 10 feet. these people that write these codes have probably never swung a hammer let alone built a house. There is no way they want everyone in upstate NY to hire some snow load case study specialist at $500 a job to do a case study before putting on a dang roof. ![]() ![]() Now it is a zoomed out map with most of NYS being blank, and written in the north east corner of Ohio, and in PA it says "CS" which means case studies. There was a zoomed in map of NYS in the 2010 codes and you could easily see what snow load to use. I was going to say it's easy to just look at the map.
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