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1st to 2nd Fl Studwall Connection Detail

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When the 2nd floor joists are parallel to the ext. wall, the 1st floor top plate is only tied in by rim slant nails and sheetrock.  The gypsum association details blocking perpendicular to the wall with sheetrock fasteners held back 7" from the ceiling-wall joint (I have assumed the holdback was for uplift situations on partition walls, but I'm not sure why they show it on the bearing wall).

If the gypsum board is to be relied upon for suction resistance (which I'm a little reluctant about) I like the perpendicular blocking detail because it brings the fastening point back from the edge.  (But at that point joist ladder blocking can be used to transfer to the subfloor, anyway.)  However, I have typically seen a parallel 2x4 block nailed to the top of 1st floor top plate, centered on the inside edge of the studwall.  The gypsum board would then be fastened to it.  This is easier to install (so in residential construction you can bet that's how many will do it no matter what you spec.) but not as good for suction resistance.

I have not seen any design values for gypsum board in tension.  It must have some tension strength because UBC allows shear diaphragm design with it (diagonal tension).  In the end, I suppose, if sheetrock is not used, perpendicular joist ladder blocking must be used.  This is never done for a standard 8' ceiling, as far as I know.  But is there any assistance to the designer to determine when it becomes an issue?  10' wall? 12' wall?  What is done in coastal areas? 

On a related subject, what about bracing the top plate at the bottom chord of a gable-end truss by running a flat 2x6 back, say 12' into the room, nailing to the bottom chord of each intersecting truss.  I have always used 'x' bracing to transfer to the roof diaphragm.  But if it is fair to use gypsum board to transfer the shear to the sidewalls, this detail would be much cheaper.  Maybe it would be preferable to use this with high redundancy, rather than using minimum 'x' bracing.

Regards,

Ed Fasula E.I.T.