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RE: Ducts Through Long Span Joists

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Contact a manufacturer like Vulcraft.  They will supply you with a list of
joist depths and duct sizes in round square, and rectangular.  Vulcraft
publishes this in their catalogue for K series joists.  

When it comes to LH series joists, the standard Warren truss configuration
is often (depending on chord size) changed to include a vertical to the
compression chord.  The ducts that run through the panel containing the
vertical element will be much smaller than the ducts that run through the
adjacent panel that does not contain the vertical element.  And as you get
near the end of the span, the verticals may go away (depending on chord

When running ducts through the interstitial space of a bar joist system,
work closely with the joist supplier and mechanical engineer.  They will
help you to optimize your layout.  I have increased the joist depth to
accommodate the ducts in order to lower the floor to floor height.  I have
also changed joist girders to a VG type accommodate the maximum duct size.  

It is also advisable to increase your joist spacing as much as possible to
make it easy (and save money) on the mechanical contractor.

Harold Sprague

> -----Original Message-----
> From:	Randy Diviney [SMTP:rsdiviney(--nospam--at)]
> Sent:	Wednesday, June 14, 2000 7:18 AM
> To:	seaint(--nospam--at)
> Subject:	Ducts Through Long Span Joists
> Is there a rule of thumb, a chart or web site to determine the maximum
> duct size to pass through a long span joist. I know each manufacturer
> constructs them differently but there must be some basic consistencies. 
> Thanks for your help. 
> Randy Diviney 
> Structural Engineering Dept. 
> Hayes Large Architects 
> Altoona, Pa 
> (814)946-0451