Lag Screws

[Engrman]

I have a 2 story condo project where the "I" joist floor framing bears on a 2 hour rated unit separation wall. The architect says he has used this detail for ten years with no objection from the local building official as long as it was detailed properly, drywall cut out around the joists, firecaulking, etc. Now the official says no way, no how can the structure penetrate the double layer of 5/8" rock and says the joists must be hung off a ledger. I wasn't particularly thrilled with the idea in the first place but let the architect talk me into it. The joists can't be turned the other way because that would screw up the HVAC trunk ducts and feeders. I can't furr out another wall under the joist ends because that would make the rooms smaller and the architect swears the rooms are too small as it is. The gyp can't be applied to the other side of the wall because it is a double wall system with the same condition on the other side. So now I have to lag screw thru 2 layers of 5/8" gyp to get to a rim joist and I'm worried about bending on the screws. In my opinion, lag screws are brittle and not very good in bending. Anybody have any thoughts or opinions?

 

[TFL]

i would not be a big fan of lagging thru 1"+ of sheetrock
what about a beam and posts instead of the details you described. that way the entire stucture could be inboard from the fire wall. from what i can tell your detail still penetrates the fire wall with lag screws

 

[boo1]

Consider bolting a beam though the drywall. With joist hangers attached to the beam. This would spreading the load out keeping stresses below drywall allowable bearing.

 

[agrant]

I have run into this problem on almost every multistory stick framed building I've done since the IBC came around. My company has come to the conclusion that if you have joists framing into a fire wall - using a double wall or adding a post and beam line at each side of the fire wall locations is the way to go. Typically we've been trying to frame the structure parallel to the fire walls wherever possible.

We have used lag screws through (2) layers of 5/8" drywall; typically adding an engineered wood product as a ledger both sides of the drywall to induce double curvature into the bolt and deal with the large bearing pressures that are induced into the wood by "cantilevering" the lag bolt.

I'm not so confident in using the drywall as a bearing material in these connections. What if it gets wet, deflects under loading, or just gets damaged in the installation process?

Some code interpretations also require that one side of the building must be able to burn and totally collapse without pulling the fire wall and the structure on the other side with it. This is obviously a bit tricky. I know some companies literally cantilever a fire wall up several stories with no attachment to either side to fulfill this requirement.

A similar requirement has also been applied to all stair and elevator shafts in my neck of the woods.

Good Times.

 

[boo1]

I never considered the water issue, good point. Since columns or furring out the wall will cost more $$, turning the floor system parallel to the fire wall is a good idea.