Tenuous Support of a truss?
Tenuous Support of a truss?
(OP)
I've got a detail that I was given to consider for a roof truss support condition. Just want you to offer some opinions on its appropriateness.
It is a flat roof (1/4"/ft slope) with triple wood trusses (parallel chords) spanning about 31 feet and spaced at 6 feet o.c. The detail calls for these triple trusses to be supported by a 2x12 ledger board that is nailed into a supporting stud wall. Roof DL is about 18 psf. Roof Snow is about 25 psf.
The detail shows a large number of nails (7- 10d) used to connect the ledger to the 2x6 stud wall. I think this is an excessive number of nails and 7 nails from a 2x12 into one 2x6 stud edge seems like we'd have split wood. This ledger carries the truss load - and specifically with trusses at 6 feet o.c. a lot of truss load might go into one ledger-stud connection.
Any opinions? Here is the detail with the large arrow showing the critical note.
It is a flat roof (1/4"/ft slope) with triple wood trusses (parallel chords) spanning about 31 feet and spaced at 6 feet o.c. The detail calls for these triple trusses to be supported by a 2x12 ledger board that is nailed into a supporting stud wall. Roof DL is about 18 psf. Roof Snow is about 25 psf.
The detail shows a large number of nails (7- 10d) used to connect the ledger to the 2x6 stud wall. I think this is an excessive number of nails and 7 nails from a 2x12 into one 2x6 stud edge seems like we'd have split wood. This ledger carries the truss load - and specifically with trusses at 6 feet o.c. a lot of truss load might go into one ledger-stud connection.
Any opinions? Here is the detail with the large arrow showing the critical note.





RE: Tenuous Support of a truss?
RE: Tenuous Support of a truss?
RE: Tenuous Support of a truss?
RE: Tenuous Support of a truss?
RE: Tenuous Support of a truss?
1. Bear the truss on top of the wall and have the parapet be built into the truss. This may require a triple top plate, or studs located directly below each truss depending on your load.
2. Provide (2) 2x10 blocking between studs at the truss locations. connect each end of the blocking to the adjacent studs with concealed flange hangers, and use another hanger to connect the truss to the blocking. If the truss hanger is close to the blocking hanger, the nails may interfere.
RE: Tenuous Support of a truss?
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Then the studs can just be installed the way they are shown now at the sides of the columns. I would also tie the column into the shearwall so it can't kick out from under the truss, probably also connect it at the top inside face so it can't roll either.
Are the diaphragm loads going through the studs to get to the exterior wall sheathing? It may be done all the time but the few times I have had a load bearing stud wall with a parapet I remember trying to avoid that.
RE: Tenuous Support of a truss?
If the blocking was intended to transfer the shear from the roof into the wall it doesn't look very well placed.
RE: Tenuous Support of a truss?
What I think I will do is generally what a lot of you implied: run the truss OVER the wall, build up wood columns within the wall (comprised of multiple 2x6's); have a double top plate running down the wall directly under the truss bottom chord; extend other 2x6 studs up from the double top plate, past the top chord to form the parapet.
This gets the truss reaction centered on the supporting wall (wall/columns) and still allows for a parapet. The chord of the diaphragm would have to be a double 2x6 running along the top chord of the truss, directly inside of the parapet - we could provide a notch in the top chord at that point to allow this chord to be flush with the top of the truss.
Thanks again....