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Re: Ducts Through Long Span Joists

[Subject Prev][Subject Next][Thread Prev][Thread Next] Randy:

Every joist manufacturer has their own standards, so there is no set of rules you can count on.  Several of them publish guidelines, but even those are not guaranteed, as they reserve the right to use whatever web geometry they want at the time of fabrication.

As long as you remember that every time you ASSUME something you are making an ASS out of U and ME, a very broad guide to give you a starting point is:

Longspans:  Assume the chords are 2" wide, the web 1.5" reclining at 45 degrees.  There will be a vertical in every top chord panel to cut the effective length of the top chord in half, but no vertical in the bottom chord panels, so that will be the largest hole.

Shortspans at least 22" deep:  Assume the chords are 1.75", the web 1", and 48" panels.  Same comments re verticals, so top chord unsupported length is 24" and bottom chord 48"

Shortspans less than 22" deep:  Assume chords are 1.5", web 1", panel length somewhere between 24" and the joist depth with no verticals except at the end panel.

On any job, if it matters you MUST specify the relevant requirements on your contract documents to ensure you really get them.


Randy Diviney wrote:

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.