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Old 04-08-2013, 06:35 PM   #1
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Floating Shelf Concerns or Design Flaw?


New to the forums, my introduction can be found at:
Hello from Northeast Illinois

My intentions were to build a floating shelf over my desk. The shelf would go around the inside corner of the wall my desk is against and have fluorescent lighting for the desk attached below.

I decided on using particle board because we have a lot in common . . . we are both cheap and easy to work with. This is not the glorified cardboard IKEA sources from a land of hopes and dreams, nor is it OSB or MDF. It is Ύ’’ “industrial” particle board, perhaps the M-2 variety?

The shelf is an L-shaped 63’’x51’’ that is 12.5’’ deep . . . It consists of 4 pieces of Ύ’’ boards (2 long and 2 short) glued together so that they overlap at the inside corner creating the L-shape with a total thickness of 1.5’’. In an effort prevent any sagging and hide the lights from view, leftover Ύ’’x3’’ boards were glued and screwed vertically onto the front of the shelf. The result is an absolutely rigid (enough) structure . . . the concern is that it is more akin to a counter top than a shelf now, weighing in at a rotund 56lbs . . .

I now worry about attaching it to the wall. My plan was to use 2x4 cut in half (to provide a flush surface against the wall), that run the lengths of both walls under the shelf and then screw the shelf into them. I was thinking 3/8’’ lag bolts into the 5 studs on both walls. Because the two sides are connected to each other, my thinking was that forces on one side of the shelf would be distributed along the opposite wall and prevent any sag/leverage on the bolts. Can studs and lag bolts like this hold 56lbs plus more weight on top of the shelf? (Say 100 lbs or more of books?) Also, I am limited in how many heavy duty shelving brackets I can use for this because of the lights underneath being 36’’ in the way on both sides.

Does this sound like it can work? Or should I turn this thing into a table and start over before I move on to painting it?

Thanks.

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Old 04-08-2013, 07:34 PM   #2
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Floating Shelf Concerns or Design Flaw?


Use bolt taps, and hang threaded rod from the ceiling joist to carry the front of the shelves. You can slide 1/2 inch cpvc over the allthread, and paint it with plastic paint. Nuts and flat washers adjust the height, and an acorn nut on the bottom finishes it off.

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Old 04-09-2013, 06:41 PM   #3
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Floating Shelf Concerns or Design Flaw?


So is it safe to assume that you think that running attachment points across the two walls would NOT be enough to support the shelf?

I am a big fan of all thread, and have hung shelves like that in a garage. I can tell you though, that aesthetically that's the only place I could get away with it in this house. I also thought about wire rope because it is a little less conspicuous, but even that will probably get a red flag.

The other thing I thought about was how a bunch of people mount flat screen TV's that weigh in excess of 100 lbs on only 2 studs . . . so maybe the original idea could work.

Are Lag Screws the best option for mounting into studs? In this situation I don't think I have to worry about pull-out, only shearing. Is my understanding correct, that lag screws are not a rated fastener and will not have a defined shear strength?

Thanks for input jagans.
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Old 04-09-2013, 08:08 PM   #4
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Floating Shelf Concerns or Design Flaw?


If I read you correctly, (Pictures would be nice here, if possible) you have assembled a "tray" out of MDF and you have screwed and glued it together. You are trying to mount this shelf (Which is heavy as hell, so we are talking some serious dead load here) onto a ledger strip to support the back and one end of the shelf, with no additional support to hold up the front corner of the shelf which will be "Hanging out i the breeze" as it were. You will then place 100 lbs of something on the shelf.

I would say that if this were solid lumber like 5/4 oak, or maple, joined with biscuits or dowels, and if it was deep enough so that the rotational force could be arrested with a moment connection to the wall, you may have a chance of it working. The materials you selected are really crap from a structural standpoint. MDF is good for some things, like a base for laminates, but thats about all I would use it for.

As far as the all thread goes, you can do it so you don't even see the all thread, but its your place, and its to each their own.
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Old 04-09-2013, 10:36 PM   #5
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Floating Shelf Concerns or Design Flaw?


Ok, I will post pictures tomorrow.

Some clarification in the meantime . . . if it at all helps.

I used Particle board not MDF, the type used for underlayment that is not OSB. It seems to have a lot more structure than MDF. It doesn't split along compressed layers.

The other ledger would not just support one end of a shelf. The "Other end" is another shelf. It is a giant L-shape. By my count the shelf would span 5 studs across one wall and 5 across the second wall.
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Old 04-10-2013, 04:49 PM   #6
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Floating Shelf Concerns or Design Flaw?


Ok here are a couple quick pictures that should give you an idea what this thing looks like.

The first picture shows the shelf as it would be positioned on the walls. I sat it on the edge of some leftover 3/4 particle board along the back edges, like it would sit on the ledger board . . . I was able to walk along the front edge without perceived deflection of the self . . . upon standing on just the far right front corner, the far left top/middle corner began to lift off of the 3/4 particle board. (Still very little flex)

The second picture shows the construction . . . two 3/4'' x 11-3/4'' boards sandwiched together with a 3/4'' x 3'' fascia. The fascia has been attached with glue and screws every 6 inches (meant to alternate top and bottom screws but accidentally did 2 every 6 inches)

Additional information:

The Lag screws I have for the ledger are Spax 5/16 x 4'' with a shear rating of 255 each. 10 total, 1 in each stud.

Would I be better off using a boxed structure underneath rather than just a ledger?
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Old 04-10-2013, 06:28 PM   #7
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Floating Shelf Concerns or Design Flaw?


I would not even think about making this a floating shelf. I would use the All thread. Particle board has very little flexural strength, and poor resistance to pull through. Frankly your shelf is not very strong, from a structural standpoint. I would use 5 hangers on this shelf, with real wood blocking underneath, and big flat washers to distribute the load. Most floating shelves I have seen use a large slab of dimensional lumber with large steel pins into the studs, and into the slab of wood.
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Old 04-10-2013, 08:34 PM   #8
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Floating Shelf Concerns or Design Flaw?


Ok lets look at this a different way then. If I want a floating shelf that traverses the inside corner above my desk . . . with the intention of putting books on it. How would you build that?

Last edited by MrChompenstein; 04-10-2013 at 08:39 PM.
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Old 04-12-2013, 01:27 PM   #9
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Floating Shelf Concerns or Design Flaw?


"The Lag screws I have for the ledger are Spax 5/16 x 4'' with a shear rating of 255 each. 10 total, 1 in each stud."

The problem is not the shear strength of the fasteners you intend to use, as that is not the weak link in your chain. The problem is the resistance to pull through that you have with particle board, which is not very good, in my experience. Maybe if you use say a 1/8 inch or heavier thick metal plate to distribute the load over a larger area between the back and the screws you intend to use, what you are proposing might work. Its worth a try because you already have a lot of work in this project. If you could drill the studs dead center and perpendicular to the wall with a 1/2 inch auger bit, and install metal drill rod that projected out the width of, and just under the shelf, I would feel a lot better about it.

Maybe Dan Holtzman will come along and resolve this issue.
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Old 04-12-2013, 04:53 PM   #10
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Floating Shelf Concerns or Design Flaw?


I think the outside edges will eventually droop----to bad you didn't ask questions before you glued that together----

A torsion box would have worked well and used the same amount of materials---Although I would have suggested lighter 1/2" plywood--

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add a 1x3 wall cleat--slip the torsion box over the wall cleat--add a few screw to the top,into the cleat---done and strong.
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Old 04-12-2013, 08:26 PM   #11
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Floating Shelf Concerns or Design Flaw?


jagans, can you clarify where I would be experiencing pull through? Or rather where a metal plate would work? The 'ledger' isn't going to be particle board. The vertical edge seen in the second image is just the front fascia, that will hide lighting underneath. (it also prevents sagging of the actual shelf part).

The 'ledger' was going to be real wood connected to the wall, and the shelf would be set on top of that wood. Screwed down through the top to prevent it from sliding off. Considering the weight, I thought keeping the board in one piece would be stronger than a french cleat, without having the cleat poking out from underneath.

oh'mike, I thought about doing a torsion box but still wanted lights on the bottom and at the time didnt think about covering them with a fascia. I still may be doing torsion boxes elsewhere in this room however.

Ultimately, this project is way ahead of schedule so I dont mind extra work. The room needs to be painted before I hang shelves on the wall. There is some wall repair to do, curtains to make/hang, closet shelving too. And now that it is getting warm in the garage, my car repairs will probably come first for a bit.

And ALL of that is on the back burner now, because yesterday we had a sump pump fail and found 1-2 inches of water throughout an 1100 sqft finished basement.
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Old 04-13-2013, 02:10 PM   #12
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Floating Shelf Concerns or Design Flaw?


Why not just put shelf brackets under it then, and mount your lights under the shelf brackets? You could build a simple box to hide the lights, if you wanted.

Personally, I think supporting the outside from the ceiling is your best bet.
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Old 04-14-2013, 10:29 AM   #13
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Floating Shelf Concerns or Design Flaw?


I misunderstood you. I thought you were going to lag the box to the wall not the ledger. If you add a piece of angle iron as shown in the illustration your shelf might work, as long as your joinery is very strong. Wouldn't a ledger defeat the "Floating" appearance?

Sorry for your troubles.
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Last edited by jagans; 04-14-2013 at 03:29 PM.
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