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18 ga steel roof decking

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We have a project with 18 gauge steel roof deck with welded connections to the roof joists to get the diaphragm capacity we need.  We always indicate the roof deck is to be lapped, but when we visited this jobsite, the deck was butted.  In some places, there is as much as a 1½” gap between the ends of the panels. 


We are concerned about the gaps and we’re concerned about the diaphragm force getting transferred between panels.  These roof panels attach to the top chord of open-web steel joists and since the panels are not lapped, the diaphragm force in one panel will have to transfer into one top chord angle, through web members or spacers between the top chords to the other top chord angle and finally into the adjacent roof deck. 


The engineer for the deck mfr indicated that 18 gauge and heavier deck is typically end lapped because the deck panels don’t nest very well.  That doesn’t make sense to me because the panels are nested to ship to the project site.  We have used 18 ga deck on other projects and have never had any complaints about lapping.


Is the diaphragm capacity compromised by the installation described above?  Is this “typical” installation for 18 ga and heavier steel deck? 



Bruce D. Holcomb, PE, SE

Structural Engineer & Vice President

Butler, Rosenbury & Partners

319 N. Main Suite 200

Springfield, MO 65806

417-861-9865 (cell)

417-521-6125 (office)

417-865-6102 (fax)