Hanging items from roof trusses


My garage has W-trusses spanning about 30 feet, the bottom edge of which form the ceiling joists.
I am interested in hanging a shelf along the width of the garage (parallel to the trusses), spanning the full 30 feet. The shelf will be constructed of four 3x8 sheets of 1/2" or 3/4" plywood, resting on a 2x4 bolted against the wall. I would like to hang the other end of the shelf from one of the trusses with cables.
In addition to the weight of the shelving unit (perhaps several hundred pounds) I estimate I'll be storing about 1000 pounds on the shelf. Of course some of the weight will be borne by the 2x4 bolted into studs, but around half the weight will be borne by the truss.
I have read that trusses have poor 'hanging strength'. Should I be concerned about this weight being borne entirely by a single truss?
Thanks, Sam
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On 3 Jan 2007 22:38:47 -0800, snipped-for-privacy@gmail.com wrote:

It is true that generally trusses are not designed to carry loads on the bottom chord. You can beef it up by running a 2x4 across the trusses at the connection points from the shelf. Be sure the wall end is setting on the gable end so that part of the load is going down the wall. Make the 2x4 long enough to catch a couple more trusses the other way. If you stick an upright 2x4 or 4x4 in the center that carries the load to the floor you will have a lot more support.
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snipped-for-privacy@gmail.com wrote:

Years ago I bought some plywood and decked out about 200 square feet in my garage attic, then loaded a lifetime of accumulated nonessential junk onto it. Some time later I noticed that my garage ceiling was bowed downward. Some of the trusts had pulled loose from all the weight I had put up there. They were swinging freely and the roof was sagging.
I had a lot more than 1000 lbs in my attic, but the weight was spread out over a wide area. I can't say that you would have the same problem I did, but it's definitely something to be concerned about. If you do go ahead with the plan, I'd recommend you only store large-volume, low-mass items up there. No boxes of books and papers -- that's what did me in.
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On 3 Jan 2007 22:38:47 -0800, snipped-for-privacy@gmail.com wrote:

Adding nearly half a ton of load to one truss will be a bad thing. You should find a way to post down to the floor. Failing that, and if this is an open truss, you should attach stringers to the TOP cords, spanning several trusses, and ignore the bottom chords entirely.
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Goedjn wrote:

OK, I've been sufficiently dissuaded from my original course of action, but posting to the floor will also be problematic (the shelf will be located over a 30' long workbench, and posts would get in the way.). The trusses are not open; I have sheetrock and insulation in the ceiling. Would one of the options below be robust?
1) Bolt several 2x4s vertically from the truss' top chord to the bottom chord, then fasten the cables into the bottom chord? This should transfer the load to the top chord.
2) Same as #1, but on two trusses. Then cable the shelf to both trusses rather than to only one.
3) Run cables from the bottom chord of the truss to the top chords of several adjacent trusses? (It would seem like this would apply lateral load to the adjacent trusses, so I'd run 2x4s perpendicular to the trusses for stability)
Thanks for the helpful advice, Sam
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snipped-for-privacy@gmail.com wrote:

Absolutely do not apply large loads to the bottom chord of a roof truss, you can collapse your entire roof that way. If you must hang this shelf, the load needs to be applied to the top chord of the truss only and should be distributed across several trusses. Even then you should check the ratings of the truss vs. the live and dead loads for the area to see how much capacity is available.
Pete C.
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