As I recall, 2-3/8" is considered full bearing.

Is there a deflection in the ceiling below?

Hi, my name is greg. The top and bottom of trusses are called chords, the 2x4 parts in your post. Placing vertical plywood will add considerable strength to the truss, however, it may be less expensive to simply add a truss in between each existing truss. This is of course you are able to get that long a truss in to the room. My suggestion is not one most home owners want to hear, involve an engineer. The fact that your truss is failing suggests that it is over spanned. I am a licensed bonded and insured commercial and residential contractor, it will be money well spent to involve an engineer.

Not really, the ceiling as a whole below is wavy. But it's not any more deflected there than in any other area. The defection is primarily in the two wood joists where the metal is bent (It's about 5/8").

Is it still full bearing even if it's laid flat (how it is here) vs on it's side? My concern is that he'll be adding extra weight to something that's already failing. Without anchoring it to the wall.

Here's another pic...

Hi Greg. Thanks I didn't know what to call it.

The contractor did actually confer with his engineer. And this was what they had decided on. But I will ask him about a truss.

Yes, it's the projection over the bearing surface.

I'd jack the dip out of the floor before adding the plywood webbing. Attach it with construction adhesive and a heavy nailing schedule.

In the picture it looks like the nailing plates on the top chord at the vertical struts have pulled away and are bent at the intersection of the nailing plate and top of the strut. That's not good and seems to be a fundamental flaw in the truss construction. I can't say I've seen residential trusses like that before. Based on that I like the idea of adding supplemental trusses or engineered I-joists as a redundant system.

I've already got part of my ceiling partially supported by lumber and plywood box beams in the attic, that I put in myself. If it were my house, I would:
Jack the dip out of the ceiling, and in fact I would crown it a bit so that when you put down new flooring, it will settle more nearly flat.
Hammer the bent flanges back into place, You may need to use clamps.
Cut 1/2" plywood into 8' strips the depth of the truss and securely nail to both sides of [at least] the two sagging trusses, using adhesive and lots of nails as suggested above. Stagger the plywood butt joints on the two sides of each truss.

This fix involves minimal material cost, just a lot of work that anyone who can saw and nail can handle.

This post was edited by airqual_guy on Tue, Oct 14, 14 at 22:55