COACH-LARGEST DUCT/JOIST COMBINATION: Overbuilding?

[IMAC85]

Hello,

I am taking this exam on monday and I'm looking at Dorf's terminology of the Joist/Duct combination.Just trying to make sure I understand what the J/D combo: the maximum Joist dimension and Duct combination on that floor. Can someone correct me if I am wrong?

Second, if I use these numbers wouldn't I be overbuilding? I always double check but I always apply the largest duct that comes out of the mech room.

I would appreciate your input.

[Coach]

I am taking this exam on monday and I'm looking at Dorf's terminology of the Joist/Duct combination.Just trying to make sure I understand what the J/D combo: the maximum Joist dimension and Duct combination on that floor.

And within areas of the same ceiling height.

Second, if I use these numbers wouldn't I be overbuilding?

No. Understand the concept and you'll know why it's not overbuilding.

I always double check but I always apply the largest duct that comes out of the mech room.

That's may not be the correct combination to use. The joist above the dust matters.

[Pow_Arch]

This means that we ought to use the largest duct found on that floor (i.e. mechanical room in the NCARB vignetter) and the joist size directly above the duct that we are cutting through?
Coach is that correct?

[textbook]

No, correct me if I am wrong....if there is a joist that is 24" and a duct that is 10" right below it for instance, that adds up to 34. But if on that same floor there is a 8" duct with a 30" joist right above it, that adds up to 38". 38" would be your largest combination even though the duct is smaller.

[Coach]

No, correct me if I am wrong....if there is a joist that is 24" and a duct that is 10" right below it for instance, that adds up to 34. But if on that same floor there is a 8" duct with a 30" joist right above it, that adds up to 38". 38" would be your largest combination even though the duct is smaller.

Correct.