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Why would you use a cleat on your shelves?

Posted by joeabbott on March 7, 2010

That was the question I got to my 2/28/2010 post called Where to start? that dealt with re-installing a set of shelves in my office that pulled out from the wall. It seems that while the attachment was “good for well over 50#”, the sheetrock was good for something quite a bit less than that!

Mike, my brother-in-law on Suzy’s side, asked with pointed befuddlement:

Cannot understand why you just did not use a stud finder and simply consider repositioning the drill holes in the cabinets with 4 to 5 inch bolts directly into the studs.

He then colorfully shares with us that “some men can … through (sic) a kid’s head through sheetrock….” Wow. OK, we can at least agree that sheetrock (also known as “drywall”) is weak, although I don’t think I’ll offer to test any theories with you. It would seem you’re comfortable with an extreme that is well beyond my experience.

But he brings up a jolly good question: what was I thinking installing set of shelves through sheetrock when it could obviously be loaded beyond a safe limit!?

Well, in retrospect it may look a bit silly, however, there were two reasons I didn’t drive the screws into studs at all attachment locations. First, the holes in the back of the IKEA cabinet were not centered on a number divisible by 16. Meaning that, at best, I could only get one side attached to a stud per cabinet. And second, Home Depot sells (although I can’t find it on their web site) a drywall anchor that holds several hundred pounds! Don’t believe me? See this spec sheet from McFeely’s on the same sort of drywall anchor I’d used. And, they work like a champ, I think … my wife’s cabinet’s are installed with the same hardware and they don’t appear to be pulling from the wall.

So, let’s look at the situation and figure out why I did what I did, shall we?

wallFirst, the wall.

Like most homes in the US, we have walls built to a standard that allows for a fir stud of nominal 2”x4” dimensions on 16” centers. The stud is finished to 1.5”x3.5” dimensions and the stud centers can vary a bit, but typically only in specific areas. The norm is 16” centers, and for my internal non-load bearing wall … it’s 16”. So it would look like the picture on the left.

wall My cabinets were sitting side-by-side on that wall and the larger of the cabinets was “hard to the right” … nearly butted up against the perpendicular wall. I’m not positive about the location of the right-most stud relative to the wall but with the cabinets appear to fall roughly as shown to the right.

If you look closely, you can see that the cabinets are drawn using accurate dimensions including their attachment location: the two little holes in the backing.

Now, about those two little holes. While our fine furniture makers at IKEA aren’t respecting US standards in terms of where their support holes line up, they are aware that they need to support the cabinets for heavy loads.

The backing on the cabinets appears to be some type of hardboard and while the name implies a wondrous strength, hardboard is pretty wimpy in both bearing and pull-out loads. But it can provide a decent shear panel if you can get the load safely into it! The comment on “wimpy in bearing” means that it’s tough to load it through specific points. But spread that attachment location out, and you have something.

Knowing this, we look at the points where they have put holes in the back and we see a metal bracket that is designed to transfer the loads from the screws to the sides of the cabinet. You see, the screw used to attach the cabinet to the wall is threaded through a small “clamp” with “teeth” on it. As you tighten the screw into the wall, the teeth on the clamp engage into slight grooves in the metal bracket attached to the cabinet.

When you’re done screwing it in …

  • the wall provides a place to screw into
  • the screw holds the teethed clamp
  • the clamp engages the grooves on the bracket
  • the bracket spreads the load out safely into the cabinet backing
  • the backing acts as a shear panel and transfers the loads to the sides
  • and my stuff sits securely in the cabinet.

By this means we have a fairly solid setup.

wall If you could have looked at the wall from behind, you would have seen this:

Notice how, when you take into account the location of the holes and the stud spacing how only one screw naturally lines up? That’s exactly what happened and the attachment point that just happened to be farthest from a stud failed.

With the cleat system we used, I was able to engage three studs for each cabinet. And I was able to keep the cabinet pushed up against the wall just like I like them!

So … I couldn’t just put holes anywhere into the backing as suggested. The two points (per cabinet) that were allowed were designed to include metal support structure. And because the hole placement was on 29.5” centers, I couldn’t hit studs by going through those holes alone. Also, I did use a stud finder … and verified my placements with my knowledge of the 16” center standard.

And, finally, I was asked why I didn’t use “4 to 5 inch bolts” to attach it. Mike probably thought I was screwing into a load bearing wall … something that used a larger stud than a 2×4 … because, in a wall using a standard stud, it makes no sense to use a screw that is long than the thing you’re attaching into. If the sheetrock is 5/8” and the stud is 3.5” … using a 5” screw would have the pointy end sticking out into our guest room. 🙂

Oh … and a simple screw is sufficient and a lag bolt (the only kind of “bolt” that could be used in this application) would be way overkill. Even for me!

And so the cleat makes good sense. As I’m sure anyone else would have come up with if they’d had all the details up front. Or, if it didn’t, you now have another option if this happens to you.

So, why did my cabinet pull from away the wall in the first place? I’m assuming that I over-tightened the anchor bolt when I installed the cabinet initially and started a break in the sheetrock that time and weight exacerbated until we finally realized a failure in the structural integrity of the wall. Sad but true … I believe I over-torqued it. Chalk this one up to user error.

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3 Responses to “Why would you use a cleat on your shelves?”

  1. Hotspringer said

    Actually assuming a .25 inch back board to the shelves and two 5/8 inch wall boards together with a 3.5 stud, you would have precisely kept the lag bolt hidden without piercing the wall of the guest room even if you used a 5 incher.

    However, I did not realize your cabinents only had two points to connect to the studs or cleats until your latest diatribe. Outstanding summation.

    Since I do not have the wood working tools you have, I likely would have bolted 3 “L” braces to back of the top board of each cabinet in aligned with the studs.
    That would have made the end bottom alignment easier to match but admittedly not as much fun to accomplish.

    Only drawback that appears evident is that the cleats end up pushing the shelves away from the wall, leaving a slight gab for stuff to fall into. Assumed you taped the back to prohibit this fall. Also assume you elected not to cut into the wallboard to align them flat in case you decide to change room arrangements.

  2. joeabbott said

    Amusing … “diatribe”. 🙂

    To the best of my knowledge, hardboard doesn’t come in .25″ thickness … where I shop it’s only in 1/8″ thickness. We’re into the guest room at that point. Perhaps you expected that and would offer the exposed bolt tip as a nice little coat hook for your company.

    As for the gap … yup, the gap will be the thickness of the cleat. And I’m a woodworker, so there’s no “tape” here. A nice strip of, I believe “elm”, secures my goodies from dropping behind my shelf.

    As for “L” brackets … may have worked but if you can closely examine the tiny pictures in the post (they are accurate) you’ll see you would be putting the entire shelf load into the butt joint between the top and sides, and that’s not advised. Again, may have worked, but your best bet is the shear panel.

    This weekend we built a path up by the chicken coop and hung gutters. We’re becoming regular DIY-ers! 🙂

  3. Hotspringer said

    Off I assume you realize I meant the “archaic” definition of diatribe.

    Looking forward to hearing more on your theory that the issue was caused by
    over torquing yet it took so long to reveal itself.

    When I have over torqued the screws or bolts in this hanging sitution I get the opposite reaction. The support immediately has been eliminated as the pieces inside the wall either break up and fall down inside the wall or rip out the wall board immediately. So I then revert to bigger brackets.

    No rush on hearing that dissertation though.

    Also on the weight limit graph presented, I believe that is just marketing. Somewhere in fine print you will see that they suggest you not trust those hanging weights when hanging items such as mirrors from a ceiling.

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