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Thread: Check my math: Storing Wood in joists

  1. #1

    Check my math: Storing Wood in joists

    So I have a workshop that consists of a long double garage, 22'x40'. The rafters are 2x6, 24" oc. The joists span 22'. The joists are open, so there is no load from drywall or otherwise. The roof is metal, so it's lighter than shingles. Walls are standard 2x4 16" oc, with a double top plate, single bottom plate.

    I have just put about 370 bf of hard maple up there, along with another 400-500# of 2x12 southern yellow pine. Total weight is probably about 1,500#, assuming a weight of 3.8#/bf for the hard maple. The load spans a space about 8'x9', or about 72 sq feet, over 5 joists.

    My understanding is you can figure about 40-50 lbs per square foot, which would be about 3,500# in this case.

    So I appear to be under the load limit for the span.

    Is this valid, or should I be considering doubling up the 2x6 joists by sistering another 2x6 to each of them?

    I'm also considering moving the load away from the middle of the span to the outside. It's in the middle because that's what seemed the easiest way to get it into the joists, and the added weight didn't seem like an issue before this.

  2. #2
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    I can't help with the engineering math, but a 2x6 that's spanning 22' clear is pretty darn lightweight...more like a tie that wasn't designed for weight bearing unless it's also part of an engineered truss. I don't know that I'd put anything up there. I could be off a little in teh details, but for that kind of distance, you'd probably normally see a 12" I-joist or equivalent for a clear span that will also support weight, such as a second floor.
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  3. #3
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    22' 2x6 is nothing more than a rafter tie, not rated for load bearing at all. There isnt a load chart in the world that rates that for 50 lb/sf.

  4. #4
    40-50#/sq.ft. is way off for 22' 2x6's- from a random search for joist load tables, "For example, in the joist span table below, the highlighted cell shows that 2" x 8" Southern Yellow Pine joists, that have a grade of #2, and are spaced 24" apart can have a maximum span of 10 feet - 3 inches (10-3) if designing for a live load of 40 lbs/ft2." https://www.mycarpentry.com/joist-span-table.html



  5. #5
    Thanks for the feedback guys, I think I'm going to take the wood down, and figure out another solution.

  6. #6
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    Quote Originally Posted by Andrew More View Post
    Thanks for the feedback guys, I think I'm going to take the wood down, and figure out another solution.
    I agree with all the comments above.

    Before you take it down, measure the distance from the floor to the bottom side of joists below where your wood is stored. Let us know how much it rebounds when you take the weight off.

    For reference
    : "A general rule of thumb for joist span is 1-1/2 times a board’s depth in feet, however, it’s not that simple. The distance a 2◊6 can span is determined by the species, grade, location, use, load, and spacing. Based on building codes, a 2◊6 can span anywhere from 2’-1” to 20’-8” depending on the affecting factors. Ceiling joists don’t normally have the same load restrictions, and so can span greater distances."
    Last edited by Lee Schierer; 12-05-2021 at 11:30 PM.
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  7. #7
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    Quote Originally Posted by Andrew More View Post
    Ö
    Is this valid, or should I be considering doubling up the 2x6 joists by sistering another 2x6 to each of them?
    Ö
    You might be able to add reinforcement to create trusses from the rafters and joists and design them to give some storage space in the center. I canít do the math but a structural engineer could. A company that builds trusses might design it for you with their software. However, retrofitting trusses would be a LOT of work and limit the access and space. Adding posts from the floor could add significant strength to the design but they would get in the way in the middle of most shops.

    A lumber rack would be a lot easier I you have room.

  8. #8
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    Engineered trusses or built in place rafters? Don't modify a truss, but you can beef up a stick built cross tie.

  9. #9
    Quote Originally Posted by Lee Schierer View Post
    Before you take it down, measure the distance from the floor to the bottom side of joists below where your wood is stored. Let us know how much it rebounds when you take the weight off.
    I was wondering the same thing. Looks like about ~1/4", at the center, assuming I didn't run into issues with doing the measurement. I did leave the pine up there for now, spread out over the same length the 200-300# should be fine.

    John J I believe you are correct, a lumber rack is likely the better approach. I don't think I'm going to be using this wood that quickly, I originally bought it to build a bench when SYP was more expensive than hardwood, and that has since gone the other way again, so I've bought a bunch of SYP to build the bench instead. Hence the attraction of attic storage.

    Engineered trusses or built in place rafters?
    Sorry, these are built in place rafters/joists, all 2x6 with a 2x8 ridge board.

  10. #10
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    Suggest you push the remaining material up there out to the edges.
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  11. #11
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    As JKJ suggests; maybe some reinforcement?

    truss-types.jpg
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  12. #12
    Too many years since I did beam calcs, but there is a BSME lurking in my history.... Lots of good advice so far (aka RUN!).

    Shifting the load to the outside will help by reducing the bending moment in the joists, but even better is to remove the load. I'd bet my entire allowance that the structure was never designed for any load other than the actual roof, some wind, and maybe a bit of snow.

    Whether stick-built or pre-fab trusses, you have a series of beams. Trying to calculate the capacity of those requires more info than presented so far:
    Roof construction? (metal, but what's under it: decking, felt, membrane, etc);
    Any collar ties?;
    Any web members? (size, spacing);
    Any rat-runs? (...what I've always called them - - they keep the rafter ties (joists) from twisting - - which will be a major source of failure).
    And FWIW, even with all this info I can't tell you the capacity ...not anymore.

    If overhead storage is the only viable option, could you add posts at a corner or edge location? This would shorten the (joist) beam span to something manageable (...<6ft??), and keep them out of the center of your workspace. Then add decking above to prevent joists twisting. Or, build a free-standing 'loft' for storage, if current joist height allows?

  13. #13
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    Quote Originally Posted by glenn bradley View Post
    As JKJ suggests; maybe some reinforcement?

    truss-types.jpg
    I'd probably go with a mono truss on either side with a horizontal tie near the top, web members bolted to rafters and bottom chord. This would leave a bit of vertical space to feed boards from the bottom.

    I would still have a structural engineer design it and specify a maximum weight distributed in the center space. It would be a shame for the load to come crashing down someday. The existing 2x8 and 2x6 members seem like a good start.

    A metal roof without sheathing doesn't provide a lot of strength so I'd probably run horizontal boards down the length of the building on top of the lower chord and add diagonal braces on either end from ridge to those supports. Of course, I've been accused of overbuilding.

  14. #14
    Quote Originally Posted by Malcolm McLeod View Post
    Too many years since I did beam calcs, but there is a BSME lurking in my history.... Lots of good advice so far (aka RUN!).
    Just to be clear the current weight is down significantly. I have removed ALL the hard maple, and just left 3 2x12x12 and 3 2x10x10s. I could probably move the remaining pine to the outside, which will further reduce the potential problems.

    Roof construction? (metal, but what's under it: decking, felt, membrane, etc); Roof rafters are 2x6 bolted onto the top plate with timberlok 6" screws. Decking is 1/2 OSB "Zip Sheeting". Then FeltBuster synthetic felt from GAF.
    Any collar ties?; No
    Any web members? (size, spacing); No
    Any rat-runs? (...what I've always called them - - they keep the rafter ties (joists) from twisting - - which will be a major source of failure). Yes, there is a 2x8 running for 10' of the 16' for the part of the building that is being used to store the wood. I am using this, and some 2x4s screwed into the joists to suspend the pine parallel to the joists.

    Quote Originally Posted by Malcolm McLeod View Post
    If overhead storage is the only viable option, could you add posts at a corner or edge location? This would shorten the (joist) beam span to something manageable (...<6ft??), and keep them out of the center of your workspace. Then add decking above to prevent joists twisting. Or, build a free-standing 'loft' for storage, if current joist height allows?
    Yeah, I'm thinking I might do something similar to what John J and Glen are suggesting with collar ties and then hanging supports on the sides. As shown in the "standard" truss type. As it currently stands there is no re-enforcement between the rafters and joists. However the local building inspector had no issues with it, and that's the design for the original 24x24 garage that's stood for 20+ years. I extended this part another 16' out this summer, which resulted in the current 40'x24'. The new addition is where I was planning on storing this new lumber.

    I think the other answer I'm hearing here is to talk to a structural engineer before trying to do much. I'll ask around and see if there are any decent ones here locally.

  15. #15
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    Other things to factor besides just weight. Distribution, wind load and snow load can be confounders.

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