4/1/19 Edit: See post #11 for repair update I cut out the soft spots to open everything up so I can dry it out. Everywhere that the ceiling was not soft and the luan was still bonded to the styrofoam, I cannot get it apart to be able to replace one giant sheet on each end. I really don't want to tear down the styrofoam as it seems to be in good condition and also don't want to destroy it trying to take down the areas that are still bonded. I went to Lowe's and home Depot yesterday and couldn't find any plywood that was thin enough to match the existing thickness. The only thing that I found at Lowe's that match the thickness is this: http://www.lowes.com/pd_15483-SS1254825-46498_4294937087?productId=3014304 I also thought about patching it in with that link above and then going over two sections with a solid piece of http://www.lowes.com/pd_518477-518477-53547_4294937087?productId=50121135 so I don't risk seeing any seams through the wallpaper but I'm wondering if it'll be too much weight pulling on the ceiling. Everything seems fairly light but I don't know what the ceiling can hold.