Doublewide roof and ceiling issues

[Tdeese]

Shingles are in decent shape. However, roof company says complete take off is needed. Replace almost all sheathing, shingles. Inside the marriage beam has dropped some and now we have this issue, some call it ghosting. The ceiling at marriage line is turning dark and popcorn ceiling is falling off. But this is the only place you see this. The ceiling from the walls in, is fine just from marriage line out. Some say the return is pulling the hot air out of ceiling at the marriage line causing condensation, as well as, moisture seeping under shingles. We have been holding off roof repair because of triple prices due to pandemic. If u have had this problem, what did you to solve your problem and how did u repair the ceiling?

 

[joecaption]

Just going by what I've had to deal with on mobile homes, what I've found is they had used just 3/8" plywood, and had used staples that had been over driven into the shingles instead of nails.
As well as all they had for venting was a few mushroom vents with no soffit vents, so they where useless.
What I did since the old sheathing was weak but not rotted was just go over the roof after removing the shingles with new 1/2" OSB, off setting the seams, and use Smart Vents.
https://dciproducts.com/smartvent-attic-ventilation/