Long story short:the paper of the greenboard the previous owners installed in the bathroom ceiling began sagging until it was about a 12" diameter circle & the paper began to crack slightly. It has been this way unchanged now for about 3-4wks. At first we thought we had water damage from our large snow, but upon inspection, the greenboard & the oak framing above it were all solid to the touch. We also know this was not caused by condensation as we do not use this bathroom to shower in. The place in the ceiling is near the outside west wall, but not touching the point where the ceiling meets the wall. The ceiling is also textured. Any suggestions on how to repair this so when we go to sell someday it doesn't look as though we did have water damage? Thanks for your help.