Ledger board connection to balloon frame construction 1

[gendyn]

I have a project to evaluate a 5'x12' balcony (60 psf LL, 10 psf DL) attached to a balloon frame construction (three-decker) along the 12' dimension. The studs are 2x4 full-size, spaced about 16" o.c. There is a 1/2" wood sheathing original to the house between the studs and a 2x10 PT ledger board1. The contractor plans to use 1/2" lag screws to attach the ledger board, but I'm concerned that, since the studs are not fully visible, the contractor may not be able to drive the lag screw perfectly centered. Is there a minimum edge distance requirement in this case?

Assuming the lag screws are perfectly centered, is there a thrust load to properly size the fasteners based on the withdrawal design value W?

Does anyone have experience with using Simpson Strong SDSW Timber screws to use under these circumstances?

Thank you

 

[driftLimiter]

SDWS or SDS screws is often my go to for this. I agree a lag into the side of a hidden stud is not going to be reliable.

Simpson has some tables with capacity for the exact condition where have 1/2" plywood between the ledger and the stud as well which is useful.

 

[Harbringer80]

Agree with the SDWS.

Assuming the lag screws are perfectly centered, is there a thrust load to properly size the fasteners based on the withdrawal design value W?

Are you trying to use the screws in tension to resist lateral? What about in plane? 1/2" lags don't meet edge distance requirements for that. You would need a row of blocking.

 

[driftLimiter]

Ya and dont take the tension through the ledger either. Use a DTT1Z or similar connection that directly transfers tension to a joist.

 

[Eng16080]

The contractor plans to use 1/2" lag screws to attach the ledger board, but I'm concerned that, since the studs are not fully visible, the contractor may not be able to drive the lag screw perfectly centered.

I would agree that it seems unlikely they would hit dead center.

Is there a minimum edge distance requirement in this case?

Refer to the NDS code for edge distance requirements, specifically Section 12.5 and Tables 12.5.1.C and 12.5.1E.

Assuming the lag screws are perfectly centered, is there a thrust load to properly size the fasteners based on the withdrawal design value W?

If you're asking what the tension force should be from the deck/balcony pulling away from the building, I would either base it on the resultant from a lateral load acting on the deck, like a wind or traction load, or the minimum deck hold-down force required in the IRC code found in Section R507.9.2, whichever is greatest. Most likely the wind load is negligible unless there are side walls. I think a traction load of something like 12 psf acting on the deck surface was discussed here on eng-tips not too long ago (with references to some research). The section of the IRC code noted requires a hold-down connection at a minimum of each end of the deck capable of resisting 1,500 lbs.

Decks and balconies scare me a lot. I generally design them so there's a direct load path from the deck framing into the floor framing of the main structure. Basically, for the deck to fall off the building, the floor of the building would have to go with it. At least that's my thinking.