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Hey everyone, I wanted to run this by the hive mind before I proceed further. I already had the guy/company that inspected our house last year come out to do a component inspection for essentially what I am asking here, except my load calculations were less than what I need now (originally told him I would only need to support a total of maybe 450-500lbs dead load.) In this image/room, I need to be able to support 350-375lbs of dead load weight from the 2x8's I will be adding across the tops of the bottom chords. My plan (based on what the inspector recommended) was to cross 4 of the bottom chords and my interior walls with (2) 2x8's via direct contact, connected with Simpson Strong-Tie 5-2/7-in 18-Gauge Steel Rafter Tie on each bottom chord it crosses. Then add wood to the bottom of the 2x8's so that I will have connection points flush with the ceiling drywall. This wood would then be connected to the 2x8's with a threaded rod all the way through with nuts and washers, with the dead load hanging from the 2x8's and not the bottom chord itself. He says this is how heating contractors would do on this type of install. Please excuse my MS Paint skills.  Same Room as Above, from the ground (the lines should be extending all the way to the other wall, I'm not sure how this got messed up)  This Room needs to support a total of 450lb's from the 2x8's, again running across all 4 of the bottom chords  Additional pictures to help get a sense of the existing structure and walls I've added    Again, when I originally talked with him, I was thinking I would need to hang only a total of ~500lbs combined in both rooms, whereas I actually need closer to 800lbs total. He acted very sure that hanging the 500lb's between both rooms wouldn't be a problem via the way described above. His reasoning was that because of the interior walls I've added as support, including the wall that runs the length of the bottom chord that divides the two rooms, and the fact that the building has been standing since the 1970s or so, that it wouldn't be an issue, if using the 2x8's to distribute the weight across multiple bottom chords. He said I would probably be fine with 2x6's across only 3 of the bottom chords, but that I could use 2x8's if it made me feel better (my words, not his) and go across 4 of the bottom chords. I have a tendency to overthink things and worry when I'm not well versed in something, and reading online about how much weight bottom chords can support has me second-guessing him. I'm not very good with math, so trying to figure out how the weight is distributed and pounds per square foot, and how that works with the 2x8's distributing the weight on each truss is just making me have more doubts. I appreciate any thoughts or advice. MarksMan fucked around with this message at 05:20 on Aug 20, 2021 |
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Aug 20, 2021 05:17
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| # ? May 5, 2024 02:12 |
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What you effectively have here is a problem straight out of a structural analysis textbook. As someone who is bad at maths that recently tried to understand one of these textbooks, I'd say you're out of your depth here and I'm not sure anyone's going to be able to chip in with a definitive answer unless they've done something very similar. That said, I don't see any giant red flags so if you trust this inspector's opinion then go for it. Otherwise you're going to need to consult a structural engineer. IMO structural analysis isn't something you can DIY unless you're referring to some pre-defined span tables (I'm not sure of any that also include point loads like this). Turns out those 6 years of schooling are important.
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Sep 2, 2021 15:54
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