Replies

1. 
   DanH | Oct 07, 2016 12:30pm | #1

   Are you saying that it's 8 feet ACROSS this "soffit"?

   And if it's two separate ducts, why can't you place a strap between them?

1. 
   biggerbob | Oct 08, 2016 07:46am | #3

   soffits...

   Yes, two main ducts next to each other with NO space in between.  Span is just about 8 feet across with load bearing bearing beam included.  I can get a strap in, but not between the two vents.  I've considered using 1/4inch sheetrock to minimize weight on the cross members under the soffit.  I have a door way that limits the thickness of what I can put UNDER the vents.  I also considered using some form of stiffener on the sides of a couple of the cross member 2X4s.....

1. 
   DanH | Oct 08, 2016 08:05am | #4

   Are the ducts running parallel to the joists or at right angles to them.  If at right angles you should be able to work a strap up between the ducts and fasten it to some sort of support bar above the ducts.  Would take some head scratching (especially to make sure the bar doesn't weigh too heavily on the ducts), but should be doable.

1. 
   biggerbob | Oct 08, 2016 09:36pm | #5

   soffits...

   running paralell.  Each main vent trunk is 34", side by side with no space between them.  I am resigned to running 8' studs and using aluminum stiffeners on every other one, and using 1/4" sheetrock.  That should help eliminate deflection.  

1. 
   DanH | Oct 08, 2016 09:43pm | #7

   You don't need any measurable space between them to get a strap (or maybe a cord) through.

2. 
   biggerbob | Oct 09, 2016 07:32am | #8

   I am now thinking that because the floor joist are cantelevered on the beams, I can get in between the joist above the vents and put some straps in.  That should solve my problem.

   
3. 
   DanH | Oct 09, 2016 09:15am | #9

   One scheme that could be made to work in many circumstances would be to bend heavy wire into an inverted U, force it up between the ducts, then slide a piece of pipe or rod through the U, either resting the pipe on the ducts (if you're confident that the ducts are well-attached) or attaching it to the "ceiling" with pipe straps.

4. 
   biggerbob | Oct 09, 2016 02:01pm | #10

   Excellent idea!!  Thanks.

2. 
   florida | Oct 07, 2016 04:02pm | #2

   Nail a 2 x 4 to the ceiling then use 1/2 Cdx to sheath the sides. Screw the drywall to the Cdx and it will be plenty stiff.

1. 
   biggerbob | Oct 08, 2016 09:38pm | #6

   The problem is not the sides.  It's the span between the two ladders...8' + almost.  As I posted, I am going to using stiffeners and 1/4" sheetrock on the underside.

2. 
   biggerbob | Oct 17, 2016 12:41pm | #11

   soffits...

   Now that I'm farther into this project, I wondered if 1/2" OSB would be acceptable to CDX?  I think the largest of the spans may need the arrangement you describe?  Thoughts?