3/24/2024 0 Comments Wood rafter span calculator![]() ![]() This might also be of interest to for the help. I also intend to have a knee wall about 3 feet in to take some of the weight so the flex will be even less. The smaller I can go the easier it will be for me to find enough logs of the right size. I also saw the the mention of "mid length" diameter for unsawn logs but no mention of it for the sawn logs.Īs far as the L/360, I intend to have the board roof on the outside be the finished interior ceiling so flex isn't much of an issue. but I wouldn't, I'd just be conservative and stay a little bigger. If this has no brittle finishes like plaster you can use the bending strength diameters and accept more sag. That will yield a roof with a max deflection of L/360. So your minimum small end dia inside the bark, ignore the max 3/10 dia flat, is ~6-1/4", midspan, where bending moment is maximum is ~6-13/16" min. For round beams Hahney says that is midspan dia and I feel that is a safe assumption for SRTB's bearing the taper rules in mind. The log standard is silent on where that is measured, only specifying that max taper is 1/8" per foot. I also wasn't sure on that I didn't know if it should be 40 and that was snow load and roof weight or if it was just snow weight and I had to add an extra 10 or 20 for the weight of the roof itself.įiguring tributary area 2' spacing x 10' span x 55 psf = ~1100 lbs total load up with a 6.8" dia in a sawn round timber beam (SRTB). Some other calculators said "horizontal span" this one just said "span". This might also be of interest to from: Don P on January 01, 2021, 07:59:49 PM Holler if any of that is unclear or just plain wrong. ![]() ![]() I'm using a span of 115" and coming up with a 6.8" dia in a sawn round timber beam (SRTB). That would be a combined live load of 40psf + a dead load of 15psf for a total of 55psf.įiguring tributary area 2' spacing x 10' span x 55 psf = ~1100 lbs total load Being steep, so longer along the slope, I'm going to use 15psf. Technically that is calculated on the slope but in common practice most folks use the same run of the roof. The dead load is usually assumed to be 10-15 psf. Next, you used the snow load of 40psf but neglected the weight of the materials themselves. At a 12/12 pitch and a 14' rafter length, the horizontal run is 10'. Note that these are normally only required to trussed rafter roofs and not for traditional purlin and rafter roof construction.I see a couple of problems, see if this checks out.įirst is the snow load is taken on the horizontal span of the roof. This is the right way to fix truss clips connecting the rafter and wall plate. Online and mobile-based calculators for determining joist and rafter spans, design connections, heights and areas, sound transmission, and energy efficiency compliance. Vertical strapping at eaves pitched roofsĪt eaves level, vertical straps 1m long should be fixed as shown in the diagram opposite at a maximum of 2m centres. Effective strapping at gable wallĮach strap should be fixed as shown in the diagram opposite with noggins between the rafters to support the metal strap along its whole length. ![]() Gable walls need to be strapped to the roof at the maximum 2m centres using 30 x 5m galvanised mild steel straps. This diagram illustrates the typical arrangement of a rafter and purlin roof and shows the dimensions referred to in the tables above. Roof pitch between 30 and 45 degrees strength class C24 Size of purlins in mm ![]()
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