Localized conditions usually point to a localized source. I went to a house last week that had some cupping around a bathroom. The plumber had been out and had checked everything. The toilet, sink and shower weren't leaking.
Cupping was evident by the bathroom door and in the hall around the corner. I used my non-invasive moisture meter to look for any kind of excessive wetness in the area. Sure enough, the floor nearest the bathroom was wetter than away from the bathroom in a nice fan-shaped pattern.
So I pulled out the big gun: my infrared camera. I do a lot of building inspections besides hardwood floors, and an infrared camera comes in handy for many of those inspections. I panned the area around the bathroom and eventually found a warm spot about halfway up the bathroom wall. A little more investigation revealed a leaking hot water pipe in the wall. This was a bit unusual as the wet wall, where all the plumbing ran for this bathroom, was on the other side of the bathroom. Apparently, this hot water pipe was feeding an upstairs bathroom.
The moral of this story is that even when you think you know construction and construction techniques pretty well, expect the unexpected. There's an old saying, "You can't see it from home," and that seems to give contractors a lot of options for doing unusual things.
Anyway, I found the source of the water causing the localized cupping and everybody was happy.
