Angled wall in closet (think under the roof- but inside closet) at 45 degree angle. Large portion of plastic is bowing (5 feet by 8 feet) due to gravity - like a bubble-there are no water marks or apparent leaks from roof. The plastic is starting to fall completely off the wall. This problem (the bow) has crept up slowly over the last few years. What can I do to repair other than tearing it out and re-plastering. If I put up dry wall what do I nail it to? It is not a problem with roof but rather an 80 year old house has plaster giving way but on a weird angle, large space and basically under the roof? Any help appreciated. I could plaster if I have too and have experience doing so but the angle and large space has me thinking otherwise.