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My metal tool shed has these studs (not sure if that’s the right word here) and I’m wondering if I should install a plywood backboard or just screw cleats directly into the studs.

The wall you see here is the only wall. There is no interior wall. If I screw into the wall from the inside, you would see the tip on the outside.

UPDATE: after closer examination, the “studs” are more like metal triangles clamped to straight metal sticking out from the wall. Hope these pics shows that… By the way, a sheet of plywood hung on these “studs” before I removed it, which is why you see holes in some spots.

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UPDATE 2: here is a crude cross section diagram; viewing it from above.

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Rib protrudes from wall. Flat end of triangle clamp thing faces the entrance.

Generic_User_ID
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    are these "studs" hollow metal, metal bent into a C shape, or the inner surface of some exterior wall feature – Jasen Dec 23 '23 at 20:16
  • @Jasen more of a Y shape. l will update my post. The wall you see in the pic is the only layer. – Generic_User_ID Dec 23 '23 at 21:03
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    As I feared these studs are appear to be the seams of the exterior wall skin, it's hard to guess how much weight they can hold. but it's probably some small number. – Jasen Dec 24 '23 at 04:47
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    Uh... didn't quite catch what you were going for with the impressionist-abstract-art diagram :-) – einpoklum Dec 24 '23 at 15:04

4 Answers4

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Think of an empty soda can with somebody standing on it. Poke the side of the can and it instantly crumples. This phenomenon is called "local buckling." Pushing and pulling on the steel flange with a French cleat will antagonize your steel studs analogous to poking the side of the soda can.

I would install a 1/2" or 5/8" chunk of OSB to the inside surface of the steel studs, and then I would attach the French cleats to this OSB. For fasteners between the OSB and the studs, I would put 1 #8 fastener down low and 3 #8 fasteners up high with 2-1/2" space between fasteners in the group of 3. I would attach the French cleats to the OSB at points midway between studs to distribute loads between studs as much as possible.

Hopefully the group of 3 fasteners will spread any pulling on the steel flange to minimize the possibility of local buckling up high. The OSB bearing against the steel flange down low should eliminate the possibility of local buckling down low. If the group of 3 fasteners lands at or near the stud's midheight, then I suggest increasing the height of the OSB to get that fastener group away from midheight (the soda can heuristic rationalizes this to my mind). The French cleats can be installed at midheight without negative consequences, however.

I don't invoke your intended loading because who knows how the system will be abused in the distant future. The best you can do to push back against such abuse is to size the group of 3 fasteners as a structural fuse that breaks under abuse. That level of complexity for some tools in a shed seems silly.

popham
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  • Thanks for this. And I should’ve inspected the ribs more closely, but I just noticed they’re shaped differently than how I originally thought. I updated my question. What do you think? – Generic_User_ID Dec 23 '23 at 21:20
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    @Generic, I just was repeating your language. I assumed that the metal wall surface bent inward to form a C shape at panel edges. I still can't see the exact shape from your images. A drawing of the cross section would be more helpful than additional photos, but I don't anticipate the exact shape making a profound difference as long as it provides a flat bearing surface for the plywood. – popham Dec 23 '23 at 22:20
  • Just in case, I added a cross-section sketch of the “studs” – Generic_User_ID Dec 24 '23 at 03:17
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    @Generic, huh. Interesting. Looks like you're stuck with self tapping or self drilling screws. The Aluminum Design Manual covers computation of strengths for stuff like this built from bent sheet material, but I'm unaware of a similar authoritative source for steel panels (I assume that you've got steel there). I stand by my answer. Especially if the manufacturer had installed the removed plywood in the same manner. I'd use self tapping screws (without the drilling tip of self drilling screws) to minimize the likelihood of the screw bumping around the back edges of the triangular section. – popham Dec 24 '23 at 03:57
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    Personally, I'd just get a couple pieces of lumber and insert+screw them into the channels at top and bottom. Then you can attach whatever you want to the lumber. As long as the loads are relatively close to the wall it should be fine—no 24" deep shelves or something like that. – Huesmann Dec 24 '23 at 14:06
  • @Huesmann when you say “a couple pieces,” do you mean two? – Generic_User_ID Dec 24 '23 at 15:03
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    Agree in principle with this, but given the new information about the ribs, I’d either buy freestanding shelving or sandwich 2x4s interior and exterior with through bolts (full height) and attach to them. – Aloysius Defenestrate Dec 24 '23 at 15:11
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    @Aloysius, the one thing with that thin sheet metal is that pressure treated wood is out of bounds. That and depending on local climate, attaching any wood outside could greatly reduce the sheet metal's life span (like a pile of wet leaves on the roof). I might use metal roof screws for any screws that puncture the skin, not that I have much faith that the rubber gaskets would cope well with years of load cycles in a tool hanging application like this. I'd be tempted to sneak blobs of cold-galvanizing spray paint into any mating surface with punctures to the outside. – popham Dec 24 '23 at 18:24
  • Good points about the pt and holes. – Aloysius Defenestrate Dec 24 '23 at 21:31
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These ribs are just folds in the wall skin, the wall skin is probably only barely strong enough to hold up the roof (because engineers!).

So you're not going to be able to safely attach any heavy cabinetry or hang any heavy tools on them.

How to attach stuff? well it's sheet-metal, so gutter bolts if you need it strong, pop rivets and sheet metal screws if it's less critical.

Jasen
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I would slip a length of 2x4 (or 2x3 or 2x2 depending on what would fit) into the angle of the metal studs and fasten this to the metal stud from the side . Then attach the wall portion of the French cleat to the 2x4. If you anticipate very heavy loads, perhaps the 2x4 could extend all the way to the floor so the floor would support the vertical load.

The length of the 2x4 could extend above and below the location of the French cleat to spread out the load on the metal stud. If you wanted to really support this you could put horizontal blocking between the vertical 2x4s to spread out the load and resist buckling, but the wall portion of the French cleat should do that so horizontal blocking would seem to be redundant.

One problem with 2x2 . . . is that many are not very straight and they can curve with age. Maybe kiln dried don't do this.

Jim Stewart
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    I just noticed the ribs are shaped differently than how I originally thought. I updated my question. What do you think? – Generic_User_ID Dec 23 '23 at 21:21
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    I cannot see the crossection of the "studs" from the pics, but I gather they are more like ribs than studs. I would put a pair of full length wooden vertical 2x4 studs under the beam at top and fastened to the floor on bottom. Then attach the wall part of the French cleats to those with screws that do not penetrate beyond the 2x4 stud. These could be with the wide fact out. – Jim Stewart Dec 23 '23 at 23:02
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    I just added a crude cross section diagram. I think you’re right to say they’re more like ribs. – Generic_User_ID Dec 24 '23 at 03:19
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    I like the direction of this design if high strength is necessary. With the shape of the "studs" disrupting your exact design, I can imagine putting well anchored 2×4 posts at both corners and spanning 2×6 or 2×8 French cleats all the way across without anchoring them to the steel. Some reinforcing of the perpendicular shear walls might be necessary, but otherwise the pattern probably achieves far better strength than using the parallel wall's bending strength. Maybe 2×6/2×8 French cleats are too skinny, though. – popham Dec 24 '23 at 10:06
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Whatever's hanging from the cleat might need an even surface below the cleat to hang against for stability.

My $.02: Without knowing what you intend to hang, how much it weighs, and so forth, the way that I would do it would be to attach plywood to the wall by screwing in from the outside, into the plywood and then hang the cleats on the plywood anywhere you want.

gnicko
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    Why from the outside? – Generic_User_ID Dec 23 '23 at 20:36
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    @Generic_User_ID This assumes that the wall is simply passed metal. So if you do it from the outside, then the pointy bits of the fasteners are buried in the plywood, and only the smooth heads are exposed. If you do it from the inside then the pointy bits will have to stick out on the exposed side of the wall. But given the update from the OP that is an incorrect assumption. However, on second thought the "studs" the OP mentioned are likely to be pressed channels that hold adjacent wall sheets together. In which case IMHO it would be best to not attach anything to them. – Peter M Dec 24 '23 at 17:59
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    In view of all this wouldn't it be best to use a pair or three 2x4 studs from floor to under the eve beam to hold these French cleats? – Jim Stewart Dec 24 '23 at 18:40