24” square exhaust fan opening in Metal Deck roof.

[ThorenO2]

Hello,

I have an existing strip/office w/ K-Series joists @ 6’oc w/ 20ga B deck (20/20 loading). Needs new 280# EF w/ 24x24 curb opening for 40” diameter exhaust. My question is with this size of opening/relatively limited weight is there an ideal installation for the deck reinforcing? I’m looking at SDI detail for roof sump opening, similar in geometry, where they span reinforcing 1-1/2” deep Zees or 1-1/2” deep Channels between joists at each side of the opening. But a 1-1/2” anything isn’t good and HR channel doesn’t seem to check out or at least it bends some.

Appreciate any input, it doesn’t seem like traditional welded curb support frame w/L4’s from the underside is in order for something like this or some type of proprietary bolted frame with lead time that costs quite a bit due to the engineering, approvals, and patents. Thanks again,

 

[dvd]

This arrangement seems very optimistic in terms of expecting the fan to always run in balance. Are there fan vibration isolators incorporated somehow? I would avoid future issues by installing a more rigid frame.

 

[jayrod12]

We often put hot rolled reinforcing on the underside of the deck.

 

[Brad805]

Most of the time you only remove the roofing you need to install the unit. In your detail you need to remove extra roofing. Installing the stiffening below is common as Jayrod suggested. In this case, sliding a 1 1/2" HSS in the existing flutes might work given you light loads.