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RE: hard ceiling direct hung off steel joist bottom chords

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There is a document referenced in the ceiling provisions of the IBC by an industry trade group (similar to SMACNA).  I’m home and don’t remember the actual name at the moment.  Inside that document, it basically exempts ceilings which are directly attached to joist bottom chords. 


If you think about it, it makes some sense.  There will be a fastener at about 12” on center, and typically joists are space no more than 24” on center when gyp. board is directly anchored.  That leaves 2 square feet of tributary area to each fastener, not much.  Also, the ceiling itself may form a diaphragm on the bottom capable of lateral loads.  The joists may only need to carry gravity loads.  See if you can find the reference and get the document.


Jake Watson, P.E.
Salt Lake City, UT


From: Haan, Scott M POA [mailto:Scott.M.Haan(--nospam--at)]
Sent: Wednesday, November 16, 2005 6:08 PM
To: seaint(--nospam--at)
Subject: hard ceiling direct hung off steel joist bottom chords


Any thoughts:


Has anyone ever designed joist bottom chords for loads hung on them from a direct hung ceiling: ie. Furring and gypsum board?  Suspended ceilings have clear cut requirements.  Is the direct hung ceiling a finish that does not need to meet architectural component requirements for a defined load path to the structure?  If you have a ceiling hung directly off the bottom of the joists – it could load the joist bottom chords with out of plane seismic forces.




Scott M Haan