Insulation adding joist?

[Canvasman]

I am going to have 2 inches of spray foam and then cellulose installed on my flat ceiling, part of which is tongue and groove paneling. Would you install rosin paper or 15# felt to trusses then nail paneling up-or just let them spray onto the wood. I'm concerned that the spray foam will lock the boards together and not allow expansion and contraction. Any thought on this?
The carpenter rough framed a joist, rite thru the center of shower, where drain is. I would like to add a joist 8inches either side of original. How is this normaly accomplished? I think sliding joist in flat, then trying to turn up will be tough since subfloor is on, or do you cut a bevel on one side giving clearance to allow it to be flipped up. 12 foot joist board.
Thanks
Eric

[Don_P]

I don't think spray foam is rigid enough to restrict wood movement. If there are any gaps it can squeeze through and show, it'll find them. I can see either way.

I can usually tip up a joist without bevelling. A "tweaker", a built up 3 ply 2x fork that slips onto the joist gives one person a lever while the second person judiciously swings the persuader.

[PEG688]

I'd cut a 30 degree bevel on opposite edges top / bottom opposite sides to roll that joist in.   You also could maybe header off with double joist hangers on either side of the shower hanging off the two uncut joist.

On the spray foam I wouldn't be to concerned about restricting the wood movement inside the place unless it's a unheated cabin that gets left for long periods unheated.  Creating a some what different critter than a house that's normally lived in.