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Original Question

I recently built a pair of custom shelves for a closet remodel. Ideally, I would like to float these shelves by securing them to some studs.

Shelving dimensions are 72"x32"x16". The shelving roughly weighs 100lbs and built with 3/4" birch plywood. The shelves would only carry the weight of common items found in your home closet so nothing too heavy. I have added 4" mounting points underneath each shelf fastened in place with 6 pocket holes.

I was thinking of using lag screws to secure them to the studs. Would this be overkill or would some finely threaded 3 1/2 inch wood screws work? Thank you in advance!

shelves

crossmember

Completion Notes

I took the advice in the accepted answer and went with RSS Rugged Structural Screws. The only ones I could find at my local hardware store were 5/16x4" RSS which may be overkill for this project but the cabinets are securely attached to studs. I think in retrospect I would go with a smaller construction screw with a french cleat system for easier installation and to make the install more aesthetically pleasing.

final closet install final closet install rss rugged structural screws

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    There is absolutely no need to overthink this, given the expected load. Let's call it 150lb all-in, spread over four screws that's paltry. I wouldn't hesitate to mount these on drywall given what I've seen from testing is the withdrawal resistance of even some fairly basic plastic plugs, and I wouldn't worry overmuch about what screws I selected either (I don't buy junk screws, but I don't buy even semi-premium ones either). Are you familiar with the Stumpy Nubs channel on YT? He did a vid fairly recently comparing the strengths of various screws and I think you'll find it enlightening.
    – Graphus
    Apr 22 at 22:36
  • @Graphus Thanks for the feedback Graphus. I wanted to make sure to do my due diligence for safety reasons. I am not familiar with Stumpy Nubs but I will most definitely check it out because I would love to learn more about this kind of stuff.
    – pyRabbit
    Apr 29 at 19:18
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    Thank you for update! Caution using such long screws, can puncture pipes or wiring behind studs.
    – Volfram K
    Apr 30 at 4:52
  • Great point Volfram! Thank you!
    – pyRabbit
    Apr 30 at 12:23
  • Lowes only had GRK #10 - 3 1/8" screws as an alternative. I was really hung up on atleast 2" in the studs since I was going through 3/4" pine plywood and 1/2" drywall. If my math serves me correctly that would have been a little shy of 2" in the stud. Someone more knowledgeable than me might say that is good or not good enough. I couldn't find any long #9 screws.
    – pyRabbit
    Apr 30 at 12:32

2 Answers 2

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A #9 GRK R4 construction screw is rated about 175lbs shear strength (actual value depends on the materials being joined). Your design will cross 2 studs, so you should be able to get 6 screws at least in your hanger boards. Conservatively, that'll give you a shear resistance on the shelves close to 1000lbs. They should also have adequate pull-through resistance. If you go with long enough screws that you get 2+ inches in the stud, pull-out resistance will be more than adequate as well. Just make sure you use construction grade screws, not a cheap knock-off or deck fastener grade.

If you want a bigger insurance policy, though, you could go with GRK RSS (Rugged Structural Screws in 1/4"). Self drilling like the R4, construction screws, but about 4X the shear, pull-out and pull-through resistance.

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  • Thank you for your very thorough and informed response! I am going to go with the GRK RSS screws then :)
    – pyRabbit
    Apr 22 at 19:45
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Since you have studs available, plus the space for four mounting points, there's absolutely no need to overthink the screw type here. I wouldn't go so far as to say you could use just about anything, but the reality is pretty close.

Here are three (of many!) published takes on the subject, each recommending different screws for the same application:
Kitchen cabinets - how do I secure them? from The Honest Carpenter [coated exterior screws]
The Screws You Need to Hang Kitchen Cabinets on Popular Mechanics [cabinet screws AKA washer-head screws]
How to Hang Kitchen Cabinets on This Old House [deck screws]

And bear in mind these are focussed on kitchen cabinets, which can on occasion be expected to hold a lot more weight in some instances than your requirement.

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  • I don't disagree that most screws of appropriate length and with the right head would hold this, but on the other hand, I see it hard to justify using a screw not intended for load bearing applications in a situation like this. We're talking about 4 or maybe 6 screws, so the difference in cost between just any screw, and an actual construction screw is at most a couple of dollars. And who knows - someone down the road might just load that shelf with books, and then try to climb it to change a light bulb. I've seen stranger things bring down a cabinet. Apr 23 at 20:56
  • The point I was making with the links is that cabinets with far greater load requirements are held with a variety of screws (and this isn't uncommon/unusual) and even that very short list includes some that are quote/unquote not suitable. And related to that, in my Comment to the OP, our perception of performance in screws doesn't necessarily match the reality.
    – Graphus
    Apr 24 at 17:54
  • "who knows - someone down the road might just load that shelf with books, and then try to climb it to change a light bulb" Yeah well, while that's certainly p o s s i b l e the plywood would be sure to fail first LOL And is basing recommendations on something like this actually reasonable? I'd say it's a fairly safe bet that practically nobody builds with this sort of situation in mind... any more than framers working in Tornado Alley use all the available mounting holes in a Simpson Strong-Tie.
    – Graphus
    Apr 24 at 18:00
  • And is basing recommendations on something like this actually reasonable? I think its absolutely reasonable to recommend a construction screw for a load bearing application such as hanging a cabinet. We're talking 4 screws or so here - why use something not rated for purpose? I think I was pretty clear that an ordinary construction screw is sufficient, and that RSS are overkill. I put them in the answer because, frankly, if someone is considering using lag bolts for this application, RSS screws (or equivalent) are far more sensible as a step up from ordinary construction screws. Apr 25 at 21:21
  • Yes of course RSS (or equivalent) screws are overkill, and it's perfectly clear you weren't recommending them. But construction screws are already overkill, as amply demonstrated by their rare use for this very purpose by people doing this sort of thing day to day.
    – Graphus
    Apr 25 at 22:30

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