How much weight can average home studs take from a french cleat?


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I am building a new bookcase that will literally just be a series of boxes, around 14" tall, and 48" wide, and mounted to the wall using french cleats. I will be using 3/4" thick birch plywood veneered in cherry. The French clear will be also 3/4" hardwood plywood, and will be long enough to be screwed into at least two studs, maybe/hopefully 3 studs. I have never tried to snap or deform a 2x4 stud, and I certainly do not want to try now. Is it possible that a bookcase of this nature will cause any damage to the studs? Oh, and I plan to make another one just like it, and hang it 8 inches or so above it, and about 12"-14" to the left. Very Mid-Century Modern design, huh? 

If studs are placed every 16", and my box-shelves are 48", I should be able to hit three studs with each box. So, there will be 4 studs involved, with the middle two studs having both boxes anchored to them. 

I do not own my home (rent), so I am sure you guys can understand my hesitance. Do you guys think I'll be totally fine? A 48" wide bookcase loaded down with thick heavy hardback reference books will weigh a lot! Trust me, I've have to move the boxes three times in one year. I know how heavy they are. 

 

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As a word of advice, use 3" lag screws, and make sure you are in the center of the studs. I've hung some pretty heavy TVs using steel TV mounting brackets. I have a 100 pound TV hanging on my wall using 4 screws, 2 in each stud through the mounting plate. 

Another reference to heavy things on studs. My lumber rack is fastened to 2 different studs with 3" spax screws and only 3 per vertical support. I've got over 300 pounds on my lumber rack easily. 

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Like Tom, I do not have an engineering-type answer.  I do have my horizontal lumber stored on shelf bracket/standards similar to these.  There are three screws per vertical and I have hundreds of pounds distributed along 16 feet of wall.

Lumber Storage 2014 (2).jpg

I also have hundreds of pounds of tools and clamps mung from french cleats with 3/4" hardwood ply cleats as you describe.

Cleat Clamp Rack V2 (27).jpg

Hopefully a licensed builder or engineer can chime in with some raw math.

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Thanks guys! This is all really great input! I thought I'd be okay, but I certainly wanted to make sure. I haven't used a stud finder in at least 10 years. So, I imagine the technology has improved and will make finding the center of the stud pretty do'able. I will definitely take your advice on the 3" lag screws. I will also rig up a v-cut block so that I can drill a 3" pilot hole straight into the studs. 

One other thing that concerns me is the design of my box'shelves. There is no support to keep the bottom of the shelf from sagging. It will be 3/4" hardwood PureBond birch plywood, and it will have a 1/2" mahogany face strip to mask the plywood "end-grain." There will also be a 3/4" back that the bottom will be screwed into and glued. The shelf will be 12" deep, and filled with very heavy encyclopedia-like hard bound books. Do you think that the bottom will sag tremendously over-time?

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I did have concern about your width span but, wasn't sure of the design.  Are you saying these will just be a plywood box joined at the corners with no other support?  a rib along the bottom would add strength,  If you want the clean "euro" frameless look, a center divider that was structural could be used.  Books weigh up fast. Check the Sagulator. Depending on weight distribution, you may actually be OK.

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3 minutes ago, Dolmetscher007 said:

Thanks guys! This is all really great input! I thought I'd be okay, but I certainly wanted to make sure. I haven't used a stud finder in at least 10 years. So, I imagine the technology has improved and will make finding the center of the stud pretty do'able. I will definitely take your advice on the 3" lag screws. I will also rig up a v-cut block so that I can drill a 3" pilot hole straight into the studs. 

One other thing that concerns me is the design of my box'shelves. There is no support to keep the bottom of the shelf from sagging. It will be 3/4" hardwood PureBond birch plywood, and it will have a 1/2" mahogany face strip to mask the plywood "end-grain." There will also be a 3/4" back that the bottom will be screwed into and glued. The shelf will be 12" deep, and filled with very heavy encyclopedia-like hard bound books. Do you think that the bottom will sag tremendously over-time?

Short answer is yes I believe that will sag. I have found that 30" wide with a solid wood lip is about as far as I can go without sag. Here is an example of 3/4" ply shelves with a 1" hardwood front that has a rabbit to except the plywood shelf. 

IMG_0968.JPG

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You can add another row of pins on the back of the case to extend the shelf width before it starts to sag. You're then looking directly at pin holes in the back of the case though. I think with a back one you can go to ~36", depending on what gets stored in the shelf. Books are heavy, feathers are not.

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My last job was to design TV mounts, if you go to Bestbuy, Costco, Walmart, Target or any other major retailer I probably had a hand in designing that mount. So to give you some idea of how much studs can hold here is the info from the biggest mount I designed. It was rated for 180lbs, so to UL standards it had to hold 4x that so 720lbs. On top of all that weight the mount extended 28" away from the wall. That would be about 1650lbs acting on the wall to hold the mount to the wall, that mount uses four 3.5" long lag bolts to hold it to the wall.

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Stud centering would also be critical if there happens to be power run beside it.  Doesn't take much to have too much angle coupled with being off-center to nick the insulation. The issue may not show up for a long time ...

Don't assume a precise 16" on-center location.  Sometimes there's a little twist, bow, or something in a stud. There shouldn't be but there is. 

New stud finders locate more than just the steel of screws and nails. They find wood, copper, and other things in the wall.  Worth the investment.  You could map/mark/verify the whole wall before doing any installation.

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I agree with the three lag bolts per stud I would use 3/8" diameter.  You want at least 2" penetration into the stud itself so add the thickness of the sheet rock and the french cleat to that to determine your minimum bolt length.  Here is more geeky structural info than you probably want:  The weakest part of the connection is the sheet rock.  Do not over tighten the lag bolts it is possible to crush sheetrock.  Structurally the sheet rock is a 1/2" empty space between the studs and the french cleat which means that you trying to bend the lag bolts slightly.  It would be good practice to keep the lag hole in the french cleat as small in diameter as you can so that you have a tight fit where the lag bolt goes thru the cleat.  Make sure that there are no threads on the part of the bolts within the cleat.  Some lag bolts have "upset threads" where the threads are a larger diameter than the smooth part of the bolt - don't use those.

Remember that the top of the shelves will pull outward slightly on the french cleat and the bottom of the shelves will push in against the sheet rock.  Make spacers the thickness of the clear at the bottom of the shelves to spread the load on the sheetrock.  This will also keep the shelves plumb.

Enough geeky stuff.

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https://courses.cit.cornell.edu/arch264/calculators/example7.1/

Paper weights about 75 lbs per cubic foot I guessed a shelf depth of 12" and got 5 cu ft per shelf which puts each unit at 400 lbs not including plywood and cleat. Worst case each stud can hold 405 lbs in a column configuration which would give you the ability to mount 1215 lbs to the wall. which would allow you 3 book cases. If the wall is load bearing you'll need to subtract how ever much load is on the stud from the 1215. Calculating that load is challenging. Odds are your fine solely because you'll never fill the entire box with books so you'll never see 400 lbs inside one.

Now if you start storing your platinum in there you'd be throwing 7,141 lbs in each unit and that might over load the system.

*Edit My paper weight estimate is also VERY high it's probably closer to 40-50 lbs but i prefer to estimate on the high side.

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Use the 5/16" x 3-1/2" of these: http://www.spax.us/en/power-lags/t-star-washer-head.html#.V03Ue4-cHtQ

Sold individually here in Lowes and Home Depot.  Don't forget to get a T40 driver bit.

I've used them to hold 2x12x16s to boathouse posts to cantilever out for "scaffolding" to build a cantilevered roof over a couple of jetski lifts.  The 2x12s had 2x8s screwed to them to get the nine feet out we needed to put the walk board on.  2 in each of the two 2x12s at the pivot point, and 2 in the short end to keep it from kicking up.  That nine foot cantilever held a 24 foot long walk board nine feet away from the dock, with me working on top of it.   I was over water, so I didn't worry about it a whole lot.  I wouldn't have done that setup above anything hard.

If that was hard to follow, simply put, they hold a LOT.

I use short ones to hold the top braces for an Alum-A-Pole scaffolding system.

I've used them a number of times since then, and never had one to break.

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9 hours ago, Dolmetscher007 said:

Thanks guys! This is all really great input! I thought I'd be okay, but I certainly wanted to make sure. I haven't used a stud finder in at least 10 years. So, I imagine the technology has improved and will make finding the center of the stud pretty do'able. I will definitely take your advice on the 3" lag screws. I will also rig up a v-cut block so that I can drill a 3" pilot hole straight into the studs.

I highly recommend this stud finder http://www.amazon.com/ProSensor-710-Franklin-Sensors-Precision/dp/B0064EICKG/ref=sr_1_6?s=hi&ie=UTF8&qid=1464737561&sr=1-6&keywords=stud+finder

or for a cheep one I have had vary good luck with a magnet stud finder like http://www.amazon.com/CH-Hanson-03040-Magnetic-Finder/dp/B000IKK0OI/ref=sr_1_4?s=hi&ie=UTF8&qid=1464737561&sr=1-4&keywords=stud+finder

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Especially being a rental I understand your concern, but the 2x4 studs will be strong enough. 

A good example: Here is a floating shelf project I did summer 2015 for a collection of antique clocks. These mechanical marvels are HEAVY. 

I had metal frames fabricated, and I used 2 - 4" lags perfectly centered on each stud for strength. 

For projects that will have the heads visible, I prefer to use fasteners with the rounded head and torx drive rather than the hex head.  For many projects, even if they are not visible, they also have a lower profile head. 

 

 

 

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12 hours ago, benny27 said:

I have the electronic stud finder that benny27 linked to and it does work pretty good except for plaster situations. But most fail at that point. 

The only issue with a magnetic finder is that if it is locating the screws or fasteners in a wood stud, they are not always centered. Sheetrock screws or nails are just run quickly and often veer off to one side or the other. If you are searching for center, that will not be of help unless you probe with a small nail to locate edges and confirm center. That is exactly what I did for the floating shelves to be sure I hit center. 

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