Our house is vintage 1956. About three years ago, we replaced the roof, siding, and soffit. Due to some unanticipated rain during the project we had some minor sagging in our bedroom. On the advice of a contractor friend, I pulled the insulation back, let it dry out, then put the dry stuff back. We decided to just wait until the next time we redecorate to fix the puckers around the screws.
The problem is that in the last month or two it's started to get worse. I've noticed sagging on the other end of the room (it's about 12x9) that was subtle enough that it took me a while to be sure it was happening. Last night I noticed sagging in my son's room, which is on the other side of the same end of the house. I'm concerned that the problem is spreading somehow.
I went into the attic to see what was going on, and everything was completely dry. I dug down to the drywall where I knew it to be sagging - also completely dry. No evidence of further moisture or old leaks (besides the one I already knew about!), plenty of ventilation, no indication whatsoever that there is a problem. It's been a damp spring (we're in northern Michigan), but it looks like the roof is doing its job.
The question is: what would cause this to start spreading now? My ****** research indicates that the drywall was put up wrong (sheets aligned long-ways with the beams so each sheet catches three beams instead of five), and I'm not sure of the thickness, but it's held up for fifty years, so why would it go funny now? FWIW, there's about eight inches of blown insulation up there, apparently in two layers, judging by the color.
Our house was built by the couple we bought it from, who were avid DIYs, but I can't complain too much without thinking about the guy who bought our last house
Thanks in advance,