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I'm planning on building storage above my garage door using an 8' x 4' platform from plywood and 2x4s. One 8' side would attach to the garage wall with lag screws. The other 8' side would be attached to the ceiling with threaded rods.

The ceiling is sheetrocked and there is living space above the garage so I don't have access to the trusses. The trusses run perpendicular to the 8'x4'. The threaded rods will connect into Unistrut or Superstrut that is lag screwed into the ceiling trusses.

I have a couple of questions:

  1. The open part of the Unistrut is facing down of course. Do I put a fender washer inside the Unistrut and lag screw through that? Or do I purchase a large square Unistrut washer, which stays on the outside of the Unistrut bottom and screw through that?

  2. What size lag screw do I use? I figure my trusses are 1.5" thick I think. Plus 1/2" sheetrock and the thickness of the Unistrut. Should I go with 3/8" x 2" lag screws?

Thanks!

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  1. I would recommend that you don't use a washer on the outside of the Unistrut bottom that has any chance of wedging the Unistrut open. The fender washer on the inside is definitely the simplest solution, and it has the advantage of leaving all of the unistrut opening clear for your platform hangers.
  2. The strength of your lag-bolt connection is based on the surface area of the threads. Therefore the length of the bolt is potentially just as important, if not more so, than the diameter. Remember, you have 1/2 or 5/8 inches of drywall that isn't giving you any grip, so your 2 inch lag bolt is only holding on by 1-1/2 inch or less. Your joists will be likely 8 to 10 inches tall. 5/16 x 4 inch lag bolts will give you more holding power than 3/8 x 2.
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  • 1. That makes sense about the fender washer so I'll probably go with that. 2. I have living space above the garage so I think the lag screws will be screwed into the floor trusses which I believe look like this (abctruss.com/floor2.jpg). So it's basically screwing into the bottom of a flat 2x4. There's a layer of sheetrock as well. So 1 1/2" of wood + 5/8" of sheetrock + thickness of washer and unistrut is probably somewhere around 2 1/4" I'm guessing. So does it make sense to go with anything bigger than 2"?
    – Jeremy
    Commented Jun 3, 2014 at 17:41
  • Ah. In that case, right, you won't get any help from a much longer screw. Now I'm nitpicking: The first quarter inch of the lag bolt is pointed so it doesn't grab the wall of the pilot hole. You might want to use 2-1/2 inch screws so you get full thread engagement all the way through the truss board. Or limit your drill depth to 1-3/4 inch using a depth stop.
    – Grunthos
    Commented Jun 3, 2014 at 19:39
  • Ah that makes sense. I like it. I think I'll go with the 2 1/2" screw and it'll just go through the truss. Thanks!
    – Jeremy
    Commented Jun 4, 2014 at 14:36

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