Best anchors for heavy cabinets on steel studs

[Chris Solar]

I'm looking for suggestions for a hollow-wall anchor sytem.

I'm building a set of wall-mounted bookcases. These will be quite heavy when fully loaded.

I plan to use a French cleat system to hang the cases, but need suitable fasteners to attach the wall-side cleat to the wall, which is drywall over steel studs, 16" oc.

The wall cleat is a strip of 3/4" plywood, 9" wide, with a 45 degree bevel on the top edge. I plan to fasten this to the wall with some kind of anchor that goes through the flanges of the studs, grabbing them from behind. I'll use two rows of anchors on this cleat, top and bottom.

So far the default choice are the standard toggle bolts with the spring-loaded wings. My only objection with these is that the hole drilled in the wall is much wider than the diameter of the bolt, so it doesn't seem like there's a really good bearing surface for the bolt to resist the downward pull of the cabinets.

Does anybody have any suggestions?

Thanks,

Chris.

[BobK207]

Chris-

I've mounted plywood strips to steel studs with the toggle bolt method & I was not satisfied with the result. Too much slop in the drywall hole, postion of strip & subsequently mounted unit is totally dependent on clamping force.

I have switched to very large coarse thread sheet metal screws (like #12 or #14). I drill the steel studs just slightly less than the screws' root diameter, drive on low speed & push like hell. The method forms a "thread" in the stud. Be careful not to overdrive/strip out the screws.

What gage studs do you have? Hopefully they're not less than 20 gage, which pretty thin.

cheers Bob

[BobK207]

Chris-

Yes I have used this technique for heavy loads (magnetic white boards), however there are few loads as heavy as a loaded book shelf.

I used to figure about 2 pounds per running inch of bookshelf when designing bookshelves.

How tall are the shelves? How close to the top edge would the strip be mounted? How deep (~10")?

So if your studs are 16" o/c that's 32lbs per shelf per stud.

If you're talking about a 4-shelf unit (~40 to 48" high & about 10" deep). The CG of your book load is about 6" off the wall, the total (per stud) book load is about 130 lbs.

If the line of action to resist the shelf pulling away from the wall is ~3" from the top & the bottom edge of the shelf bears against the wall you have a resisting "couple" of about ~36" minimum.

If my way of looking at it makes sense; we've got 6" x (130lbsof books

• 25 lbs of shelf)

Or (torque yanking bookshelf off the wall) 930 in-lbs resisted by a

36" couple>>>>>

Need ~25lbs of safe allowable withdrawl per stud location. We also need 155lbs of safe allowable shear resistance per stud location.

I'm was concerned about shear loading than withdrawl but that's just my point of view.

I'm talking about burly #12 or #14 SMS not POS drywall screws. Should be able to get a lot more than 25lbs withdrawl safely out of a #12 unless your studs are paper thin.

btw any idea stud gage? anything less than 20 & I'd get worried.

Anybody willing to verify / correct my assumptions & calcs? The are just "seat of the pants" but they seem reasonable.

Chris, I guess we should also consider the "unanticipated" load, extra

125 lbs point load; painter using the shelf as a foot hold. I've done that dsort of "extra" loading.

You could whip up a small frame out of plywood, sawn lumber or MDF & do a quick experiment. Screw it the to wall with the bottom ~4" off the ground & then stand on it.

Or you could install a SMS thru a piece of 3/4" ply, leave the head proud & see if you can pry bar it out. Figure you mechanical advantage on the pry bar (10 or 12 to 1?)

One good test is worth 100 expert opinions. :)

cheers Bob

[BobK207]

Better yet, checkout

SteelFraming/4298_Hybrid_Steelguide_2.pdf -

page 6 of the pdf; page 24 of the "paper" document

looks like you'd have capacity to burn even if the struds are only

33ksi material

If you counter bore your plywood big enough & deep enough to accept the driver socket & screw head; you could use self-drilling screws & really scream through it.

Bob

[Chris Solar]

Thanks for the reply...that confirms my suspicions.

I guess the other option is the E-Z Toggle

I'd still have to drill a fat hole in the drywall and stud, but at least the body of the anchor is the same size as the hole.

(I assume that the teeth on the end of the anchor are only capable of drilling through drywall, and not the steel stud.)

Using sheet metal screws sounds appealing from a cost/convenience perspective, but I worry about the pullout resistance. Last thing I want is to have a few hundred pounds of book/shelf coming down on someone's head. Have you used this for heavy loads?

-Chris.

[Chris Solar]

The largest section of shelving is 65" wide, 37" tall, and 9" deep. It has three rows of books (183 linear inches of bookshelf), so almost 300 pounds for a fully-loaded unit based on my measurements. It's hanging up near the top of a 9' ceiling, so I don't think it will make a convenient step-stool for painters...but then again someone reaching to get to that top shelf could fall off their chair/ladder/pile of phone books and attempt to use a shelf as a grab bar on the way down.

The mating surfaces of the French cleat will be about 3" below the top of the unit, as you guessed.

I don't know what gauge the studs are; this is not for my house.

The wall cleat will span five studs, so there's 60lbs (shear) per stud, and at least two fasteners per stud.

In addition to the French cleat along the top, I was going to fasten a 3" strip of the same 3/4" plywood along the bottom, and the cases will be screwed to these through the backs. The upper cleat is what's really meant to take the load, though.

I suppose I could go with a hybrid approach: put a row of EZ-Toggles along the top of the main cleat (where the pullout loads are greatest), and put another row or two of fat sheet metal screws lower down to finish the job.

Thanks,

Chris.

[BobK207]

If you're going to screw the bottom edge, doesn't that defeat the French cleat method. Why not just screw it top & bottom and be done with it?

I suggested the SMS's because I hate using most wall anchors; they're a pain to work with & not very strong.

cheers Bob

[Chris Solar]

The screws along the bottom are just to keep the lower edge of the cabinets snug against the wall once they're in place.

-Chris.

[Goedjn]

Not that there's anything wrong with your method, but If you can measure accurately, you can accomplish the same thing by using two cleats. Of course, then in the next earthquake, the whole thing will bounce off the wall and kill you.

[Chris Solar]

Here's a follow-up, for the record:

I went through a few (expensive) boxes of fasteners before finding something I trusted.

Regular wing-toggles were no good. For one thing, they require a huge hole relative to the size of the bolt. For another, you can't install the anchor independently from the bolt and the fixture -- and I didn't want to wrestle with getting a dozen toggles into their holes while holding the wall cleat in the air.

The EZ-Toggles were a disappointment. They can only handle a wall thickness of up to 5/8", and when they're going through 5/8" drywall _and_ a steel stud flange, the toggle didn't always pop open inside the wall. That's a pain, since it can't be fixed without taking everything off the wall. Some of the walls in question also had two layers of 5/8" drywall, so these wouldn't work anyway. Last, the bolt that goes into the anchor is pretty skinny.

Fat sheet metal screws -- the self-drilling kind -- were no good. They had hardly any pullout resistance. Maybe the self-piercing kind would have worked better.

Finally: Toggler brand toggles

These were good. They're easy to install, since the anchor is installed on its own, without the bolt. For a 1/2" hole in the wall, I got to use a large, reassuring 1/4-20 bolt. The anchor itself is substantial, and has actual threads, so it's more like a nut than any other anchor. I found them locally (Ottawa, Canada) at Fastenal I think HD carries them in the States.

-Chris.