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I am lowering a 10' x 10' section of the ceiling in my home for cosmetic reasons (to define an area) by about six inches lower. I plan to frame it like a soffit/bulkhead, with multiple long parallel "trusses". I had originally intended to frame it like long but shallow walls, with 2 x 4 top and bottom plates with short studs in between (like a ladder.) I would place these perpendicular to the ceiling trusses, mounted 16" on center. Exposed sides would get OSB for something more to nail to. Hope that makes sense. This structure would then be drywalled.

I realized that, since the lowered ceiling will be six inches, instead of building the long "trusses" ladder-style with short 3" studs between the two long top and bottom plates, is there anything wrong with simply sandwiching short pieces of 2 x 4 parallel instead of perpendicular (since it would equal six inches?) In other words - looking at one of the "trusses" of the structure from the side, the bracing between the top and bottom would run parallel instead of perpendicular - "stacked" if you will. Any issue with this in terms of strength, etc. since it will be carrying drywall?

Edit - what about a cleat and 2 x 6 joist, like this diagram @isherwood?

enter image description here

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    Would use 2x6s instead. Single 2x6 will be 5 1/2 inches plus 1/2 inch drywall will give 6 inches. Wood be cheaper also. Think code for living spaces is ~7ft minimum. Should be okay with 8 foot or greater ceiling height.
    – crip659
    Aug 25 at 18:48
  • Actual size of a 2x4 is 1 1/2 x 3 1/2 inches.
    – crip659
    Aug 25 at 18:55
  • These are ten foot ceilings, so height is not an issue. The main reason for my plan is that it's only part of a larger room (above a wet bar) and it's a corner, so the only place to attach laterally are two perpendicular walls. If I had two parallel walls to attach to, I'd just run new joists. And I'm trying not to tear the existing drywall down to attach to the existing truss structure between floors if I can avoid it.
    – Lee
    Aug 25 at 19:10
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I reject both of your ideas as being way too lumber-intensive, particularly in this time of global price inflation. They're also too much work and too complicated. You should be suspending single joists (2x4 or 2x2), not building walls or trusses. Those are for load-bearing situations. A top plate in such a case does nothing for you.

Don't build anything--just hang new joists. That's all the situation calls for. Float your new joists below the old ones, and use scrap blocks at the horizontal intersections as suspenders. If you're using 2x4 joists, orient them upright and just hang them every four feet or so.

Leave them short on all sides so you can then nail on a rim joist. This could be just OSB ribbons to act as drywall backing.

Also, don't rely on pullout strength in nails. All nails should be horizontal, or use screws. You don't want them wiggling out over time in a vertical use situation.

PLAN VIEW

      | |<-- old joist      | |                   | |
      | |                   | |                   | |
   ___| |___________________| |___________________| |___
  |___| |___________________| |___________________| |___|<-- new joist
      | | |                 | |                   | | |
      | |_|<-- hanger       | |                   | |_|<-- hanger
      | |                   | |                   | |


ELEVATION VIEW

       _                     _                     _
      | |<-- old joist      | |                   | |
      | |_                  | |                   | |_
      | | |                 | |                   | | |
      | | |                 | |                   | | |
      | | |                 | |                   | | |
      |_| |                 |_|                   |_| |
        | |                                         | |  ||
        | |<-- hanger                               | |  ||<-- rim
   _____| |_________________________________________| |__||
  |     | |                                         | |  ||
  |     |_|          new joist                      |_|  ||
  |______________________________________________________||

Another idea, now that we have a clearer picture of the situation...

Just build a standard framed 2x4 wall and hang it using suspended ceiling screws and wire. One hanger every 40" (since you mention an odd 20" truss interval) in both directions should be plenty. You'll want to brace it diagonally to prevent sway after it's all hung and level.

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    @Lee It's just framing lumber and drywall. You do not need to attach to the walls, just to the joists that are in the ceiling above the existing drywall. Aug 25 at 19:10
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    Exactly. I made no mention of walls.
    – isherwood
    Aug 25 at 19:10
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    The bottom chord of a ceiling truss is also a ceiling joist. You could also hang with steel hardware or wooden cleats screws into them. Doesn't really matter.
    – isherwood
    Aug 25 at 19:14
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    Nope. Many types of threaded hardware will do the job. Just don't rely on nails installed vertically.
    – isherwood
    Aug 25 at 19:20
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    You should be able to just pull it up a corner at a time with some wire. The entire frame won't weigh much.
    – isherwood
    Aug 25 at 21:13
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Dropped ceilings like you've described are a routine thing in commercial construction. I haven't done commercial construction, but I do have a habit (hobby?) of noting whatever details I can observe when I'm in a building..

Do a web search for "suspended drywall ceiling" or "drywall suspension system". You'll find tee and hat-shaped steel products from brands including USG, CertainTeed, and ClarkDietrich. Some are stocked by national home center chains; for others you'll have to figure out who are the building supply companies in your area.

These are lightweight and easy to work with. (I've used hat channel for furring but never built a suspended ceiling.) The weight is borne by wire ties secured to the structure above -- in your case, with wood structure overhead, an eye lag screw would be a likely choice. The weight of the suspended ceiling is carried by ties that go straight upward; sway of the assembly is controlled by wire ties or by rigid members that go upward at about 45 degree angles.

Here's an eye lag screw (illustration: www.homedepot.com)

eye lag screw

.. and here are a couple photos of a suspended drywall system to feed the curiosity. (photos: www.kuikenbrothers.com)

close-up drywall suspension system

partial covered drywall suspension system

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  • I would never imagine that would be enough to hold drywall. Wow.
    – Lee
    Aug 25 at 21:56
  • @Lee I wrote that I'd never worked in commercial construction. Not completely true; I did install fire alarms for a while. One project was a new gym; I got a good look at their building. The roof was 25 ft above the concrete slab floor; a mezzanine (partial second floor) held some of the exercise equipment. Locker rooms were on the ground floor (not below mezzanine) and had drywall ceilings about 10 ft above the slab -- they were suspended with a system like this about 13 feet down from the roof! It seems to be common where a story is 12-15 ft but they want drywall suspended at 9-10 ft.
    – Greg Hill
    Aug 25 at 23:29

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