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Lag screws through 5/8" Sheetrock
3

Lag screws through 5/8" Sheetrock

Lag screws through 5/8" Sheetrock

(OP)
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

RE: Lag screws through 5/8" Sheetrock

No, the drywall will fail in bearing loading.

RE: Lag screws through 5/8" Sheetrock

(OP)
Thanks for your quick response.

If the drywall is removed it seems like the lag bolts would be a better anchor than 16p nails.  What size would be appropriate through an 1 1/2" ledger?

Also, could one support a 3/12 glue lam ledger at intervals, attaching with lag bolts to the wall through the drywall?  In this way the bearing load would be on posts under the ledger.

Jim

RE: Lag screws through 5/8" Sheetrock

Seems to me that nails are far preferable to lag bolts in terms of part cost and speed of installation.

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RE: Lag screws through 5/8" Sheetrock

(OP)
Although it would be quicker I think that the lag bolts would be better.  It still seems to me that a long lag bolt through the ledger (1 1/2" x 12") and the 5/8" drywall would have bearing capacity since the anchoring would be in the 2 x 6 studs (16" on center).  In my case cutting through the 5/8" would cause a large mess and is difficult in the situation.

We had one where we lag bolted a ledger through a 1/2" plywood over a 2x4 wall.  I know the drywall is different but it seems that there should be some way to get some bearing.  Would it be possible to angle the lag bolts upward into the 2x6 or is there a specialty (eg Simpson) hanger that would accomodate this?

The load on the mezanine is hot excessive using 16" on center 16' TJI 230 joists.  With a 100 psf storage loading and 10 psf dead load.  The glue lam that the joist attaches to is a 6 3/4 x 18 spanning about 19 ft.  If I had to I could put a glue lam against the wall and support it with posts I suppose.

Jim  

RE: Lag screws through 5/8" Sheetrock

How is there bearing capacity conferred by the lag bolts?

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RE: Lag screws through 5/8" Sheetrock

(OP)
I believe that the lag bolts could add enough additional holding power to compensate for the distance of 5/8" and the fact that drywall has no load bearing capability.  The compression afforded by the lag bolts and the fact that they would have much more bearing capacity than 16p nails could help.  

Angling the bolts upward into the studs could improve load bearing.  

In addition I could support the ledger with periodic 2 x 4 posts attached to the wall studs.  Thus, anchored horizontally with the lag bolts and supported vertically by essentially cripples, I believe it would hold.

Thanks again,

Jim

RE: Lag screws through 5/8" Sheetrock

Doesn't your specification mandate that the ledger be fastened to the studs? Seems to me that that precludes the option that you're considering.

I guess I don't understand your application because I still don't see how the lag bolts provide any "holding power" that opposes a bearing load being applied to the drywall.

Are you sufficiently confident in your approach to stamp the drawings?

Does your approach conform to UBC requirements?

--------------------
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RE: Lag screws through 5/8" Sheetrock

(OP)
You are probably right and it is tempting to just say that the drywall has to be removed for attachments.  I believe that the concern was to set up a situation where the mezanine could be easily removed for a future tenant.

The main concern was to make something that would be more easily removable.  Puttying holes is easier than a new drywall job.  There is still the option of using glue lam beams supported with posts up agains the drywall.

Jim

RE: Lag screws through 5/8" Sheetrock

Both Simpson and USP manufacture high strength screws:  SDS and WS screws respectively.  The issue with keeping the drywall in place is placing the fastener in bending.  There has been some research done on the diminished capacity for this condition.  Contact either of those manufacturers.

RE: Lag screws through 5/8" Sheetrock

(OP)
I found Simpson Strong-Drive information at http://www.strongtie.com/products/connectors/strong-drive-screw.html
My lbs per lineal foot on the mezanine is 660.  Sounds like three rows into 2x6 studs at 16" oc would accomodate this quite well if not the ability to adjust for the bending factor.  There was one article at http://www.fpl.fs.fed.us/documnts/fplrp/fplrp469.pdf#search='lag%20bolt%20capacity'
but there was not a lot of particulars.

Jim

RE: Lag screws through 5/8" Sheetrock

(OP)
Common sense would tell me that even given the offset three 1/2" x 5" lag screws into a stud through LSL ledger and 5/8 gyp board would be better than 3 16p nails through the LSL ledger into the same studs.  However, I am not finding much to support it.

Jim

RE: Lag screws through 5/8" Sheetrock

Jim, Contact either Simpson or USP via phone and ask to speak with on of there Professional Engineers.  I have found them accomodating and easy to work with.  I am sure they have run into this scenario before.  Further, Virginia Tech has done some testing of this additional bending as it pertains to bolts for ledgered decks.  There is 7/16" OSB sheathing plus (sometimes)drainage washers between the ledger and band/rim board.  They developed a reduction factor which accounted for the bending on 1/2" bolts.

Jordan

RE: Lag screws through 5/8" Sheetrock

(OP)
Will do.  We have contacted them regarding venting and found them to be helpful as well.

Jim

RE: Lag screws through 5/8" Sheetrock

(OP)
In talking with the engineer he acknowledged that although there is nothing made there is a demand for a fastener that would work with gyp board or sheathing.

The only cantilevered fastener system was their ICF Ledger Connector System made for foam filled concrete walls.

Probably the only options without cutting the drywall would be to bolt the heck out of it and support it periodically with 2x4's lag bolted vertically to the wall.  I am pricing also using 3 1/8 x 18 GLB that would have appropriate post placement.  Although it is not necessary I would probably lag bolt it to the wall as well.  

Jim

RE: Lag screws through 5/8" Sheetrock

Jim,

I saw your post and had a couple of questions.  In order to get the full NDS design value for a lag bolt, the penetration needs to be 8d, (4" min. for 1/2" diameter bolt), with a minimum pentration of 4d.  If your load is 660 plf, a 1/2" lag has an allowable of 220 plf, you would need 4 total at 16" on center.  How deep is your ledger?  The spacing between bolts may be an issue.  Is this a 2 hour rated shaft wall?  This is an issue with stair wells that are wood framed.  The gyp can't be penetrated and a ledger beam is needed to support the floor framing.

Another option if the situation allows it would be to place a two ply LSL board in the wall framing.  The gyp would be able to run past.  Provide a double LSL ledger board and connect it to the beam in the wall with thru bolts.  The connection would require less bolts.  It may work depending on your situation.  

RE: Lag screws through 5/8" Sheetrock

(OP)
Thanks for your response.  The ledger is 1 1/4" and the depth is variable to around 16".  The wall is 1 hour fire rated 2x6 with 1/2" plywood covered by 5/8" exterior fire rated sheating with Hardi Board siding.  

I was thinking of using 6" x 1/2" plated lags.  A friend suggested I use Simpson SDS structural screws (probably 1/4" x 6").  

The wall is already in place.

Jim

RE: Lag screws through 5/8" Sheetrock

(OP)
I should note that the interior wall where the attachment goes is 5/8" type x gypboard.  From interior to exterior it has 1/2 gyp, 2x6 Studs, 1/2" plywood sheating, 1/2" gyp exterior sheating, Hardi-Panel 3/8"  panel.

Did your calculations on the 1/2 lag at 220 lbs per lineal foot take into effect the 5/8" for the gypboard?

Jim

RE: Lag screws through 5/8" Sheetrock

(OP)
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.

RE: Lag screws through 5/8" Sheetrock

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.

RE: Lag screws through 5/8" Sheetrock

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.

RE: Lag screws through 5/8" Sheetrock

(OP)
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

RE: Lag screws through 5/8" Sheetrock

(OP)
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

RE: Lag screws through 5/8" Sheetrock

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.  

RE: Lag screws through 5/8" Sheetrock

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


Jim

RE: Lag screws through 5/8" Sheetrock

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.   

RE: Lag screws through 5/8" Sheetrock

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.

RE: Lag screws through 5/8" Sheetrock

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.

RE: Lag screws through 5/8" Sheetrock

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

Jim

RE: Lag screws through 5/8" Sheetrock

(OP)
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

RE: Lag screws through 5/8" Sheetrock

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.

RE: Lag screws through 5/8" Sheetrock

(OP)
So did my engineer.

Thanks,

Jim

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