The length of the ridge is 40', and assume it has 4 supports, one every 10 foot. The ridge is down the center of the house, so taking 15' as the total amount of length the ridge board could possibly have weight from. The rafters are 2 or 3/12 slope so it's fairly flat. Then I take the length of the ridge board and divide it by the number of 2x4 braces coming off of it going on load bearing walls or beams, then multiply the roof dead load + live snow load by the number I got when dividing ridge length by number of braces.įor example, assume the house is 30' wide. I assume I would take the horizontal (not sloped) depth/width of the roof, divide by 2 to gather what the ridge board could potentially be bearing (even though it's not a ridge beam). The roof is not relying solely on this one beam but the ridge board is getting some support/help from this beam during those snow load times. However, the calculation seems much more complex but I believe I have a rough idea to figure it. Our region is specced out for 20PSF snow load. I'd like to calculate the dead roof load of shingles, sheathing, framing but more importantly snow load during those times it is wet and heavy. I would like to also be able to calculate for example if this beam did that load and then had some 2x4 braces coming off the ridge board on the older stick-framed roofs with rafters and the collar tie system. This is all just for the beam supporting the figure of 20PSF for attic load and not roof load. So as a correction if using the GP Lam sheet from original, no dividing the 280PLF! In which the correction is two plies of 16" for their rating of 315PLF or 3 plies of 14" for their rating of 320PLF for span of 22' with 元60 rating. The PDF I linked in this post for pham shows individual 1-3/4" only which is why I was originally doing the math and dividing by plys at an earlier time. What do you mean by loads are probably wrong unless it's really low attic space? Please share! Are you talking the 10PSF live load factor? I'm here to learn and make sure I - That was my mistake in typing late and mixing the PDF's. I am a little more familiar with this companies' tech sheet. I traditionally follow the LVL manufacturer specs for fastening them - I meant to link this ONE. RE: PLF Calcs for LVL Beam Luceid (Structural) 28 Apr 23 - Building LVL beam consisting of multiple 1-3/4" LVL sorry if plys was confusing there. I was considering using the percentage change from their roof PLF (240) to their floor PLF (360) and multiplying that ratio to the numbers but I'm sure that's just shooting in the dark. It seems too easy simple, and I'd also like to know of any quick formula perhaps to convert the PLF rating of the LVL for less deflection like L480 when their chart maxes on 360. and the first LVL to do 280 with 3 ply 14".Ĭan someone please tell me if this is the correct process, assuming I had a correct PSF to start with? I'm just looking for confirmation that I am not missing something here. When I comb through the chart, I locate 22' for the span and go across on the "Two 1-3/4" GP Lam LVL" (and three) to find the first LVL that can do 280 with 2 ply is a 16" LVL. I scroll down to the Allowable Uniform Floor Loads because it uses at least L/360 in this case since it is drywall that would be sagging here. In this case, the Georgia Pacific GP Lam LVL tech sheet has 1, 2, 3, and 4 plys already built in. I then divide this by 2 and 3 to find my individual PLF capacity needed for 2 and 3 ply of LVL EDIT:If using a chart for single 1-3/4" only. I'd say that is more than 10PSF but online searches seem to treat person in attic as 10PSF?įor the first part of this, I am taking 20PSF x 14' (half the 28') to get my PLF of 280. 5PSF for attic dead load of insulation and 2圆 framing (stick framed with rafters, ridge board, etc and not webbed truss), 5PSF for two layers of drywall/mud, and 10PSF for what would be live load of someone crawling around in attic. I was going to use 20PSF for this rating. The ceiling joists have 5/8" drywall - let's say 2 layers - and then attic space above with blow in insulation. The ceiling joists are for two rooms, each room for this example has a length of 14' so the "Span Carried" would be 28' but technically when I run the PSF I would halve this I assume? A LVL beam to be installed to support ceiling joists that are *not* continuous, as in they tie into the LVL beam. I believe this is the PLF rating? It seems a little too straightforward using the tech sheet so I want to make sure I am calculating correctly. I'm wanting to learn how to properly size an LVL beam when the specifics do not simply fall under the manufacture's generic span chart giving two options for premade spans.
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