Lag screws through 5/8" Sheetrock 3

[CUBUFF]

I have a specification in a project for a ledger to be attached to 2x6 studs on 16" centers to hold a mezanine. The specification states that the drywall is to be removed and the ledger connected directly to the studs using 16p nails.

Could one use long lag bolts (say 5/16" x 6" and attach through the drywall instead?

Thanks,

Jim Marshall

 

[CUBUFF]

Oops, it should go From interior to exterior it has 5/8 type x gyp, 2x6 Studs, 1/2" plywood sheating, 5/8" gyp exterior sheating, Hardi-Panel 3/8" panel.

 

[DTGT2002]

Going back to boo1, the drywall will likely crush when your loads are applied, leaving the fastener to span in bending. I imagine the drywall manufacturer could give the face compressive strength and that may let you know if it can transfer the load.

 

[vpj]

Jim

The 220 plf allowable is from the 2001 NDS Manual for Wood construction. If the wall is constructed and sheathed, lag screws would be the best option. I would check with a local engineer to give you a sketch showing the spacing requirements for the bolts and a bolt size that will work. What is commmon practice in one area is not common everywhere. Good luck.

 

[CUBUFF]

You are right on this one. A contractor friend pointed out that if you use a larger ledger the compression on the drywall is going to be much less of a factor. In addition he says that he finds lag bolts much preferable to nailing due to the fact that the withdrawal value on lag bolts is much higher than nails and has found most failure linked to that.

He suggested a couple of over-building techniques. First, use a large ledger with multiple lag screws. Drill pilot holes for the lags through the ledger into the stud (says anyt lag over 1/4" needs a pilot hole. Then, use the pilot hole to bore a 1" or so hole through the drywall. Insert washers flushwith the drywall, bore the ledger and install the lag screws.

Secondly, he said if one is really concerned to lag bolt 2x4 flat against the wall to the floor to support the ledger.

Oddly enough I found that the lateral load value on a 5/16" lag screw is not appreciably less than a 1/2" lag bolt (220 vs 290 for 4" lag penetration in main member).

Thanks,

Jim

 

[CUBUFF]

VPJ

You mentioned a concern about the placement of the bolts. An article from California Falsework manual Suggests a minimum spacing of bolts in a row to be 4D (diameter of bolt) with end distance at 7D from either end when in tension or compression. They also have an adjustment factor for multiple bolts relating to the cross sectional area of the main member, bolt spacing, and number of rows. The lateral load of the bolts are added and then adjusted depending upon number, main member, and bolt placement.

Jim

 

[vpj]

The 4D and 7D numbers match the NDS specifications.
I like the idea of notching out the drywall locations at the bolts and add the washers. A good way to keep the drywall from crushing.
The pilot holes are necessary to help keep the wood from splitting.

 

[CUBUFF]

Bottom line--do you feel that this approach is defensible over say post and glu-lam beams?


Jim

 

[vpj]

If the numbers work for lag screws, this would be a much simpler fix. The design calcs would need to be run through to get the actual sizes and spacing, but this would be a cost effective solution. In my opinion, this would be similar to how 2 hour shaft walls are framed in wood apartment buildings around stairs and elevators.

 

[AbelGus]

Use a 1.5" or 2" diameter hole saw to cut out the dry wall. The pilot drill for the hole saw will work as the pilot for 3/8" lag screws. Then use stacked 1.5" or 2" diameter fender washers for the bearing. Make a template from 3/4" ply for the size of the ledger. Use it locate the holes in the gypboard and the ledger so that they match.

 

[Ron]

Cut the drywall and fasten the ledger directly to the studs. To sandwich a weak plane in a critical structural element is not a good idea and is not defensible.

As for lag bolt vs. nail, either will work with adequate capacity. You'll obviously need more nails than lag bolts. In wood construction, it is better to keep the diameter down to minimize splitting. Stagger the bolts, also.

If you leave the drywall in place, the lag bolts will be under combined shear and bending. Check the interaction....it probably won't pass.

 

[CUBUFF]

I am having an engineer check it out using 3/8" lags and Simpson bolts.

Jim

 

[CUBUFF]

I had the engineer check it out. We are using 4 Simpson SDS screws per stud.

I also came across some information regarding deck attachment failures in Colorado. It seems that the 16d nails that everyone specifies have little holding power (although I am sure they have the shear originally) and the decks were slowly separating from the house and then collapsing.

Perhaps these requirements need to be revisited using bolts instead of nails.

Jim

 

[kmead]

CUBUFF,
This may be a very late response, but I just wanted to tell you that I have specified the lag screw connection through the drywall in cases where the wall is fire-rated and the ledger is not allowed to interrupt the drywall. It may not sound like a good detail, but it works and I have never had any problems with it. I would say as long as the loads are reasonably low, go ahead and attach the ledger with lags through the drywall.

 

[CUBUFF]

So did my engineer.

Thanks,

Jim