A very interesting problem.
I'm not surprised much anymore in this industry. I have run across just about every issue that can go wrong with a home. Some so much, I can tell what the problem is over the phone with very little information. The issue we ran into this week was a new one for me!
The property manager contacted me after getting complaints from the tenants. Several other guys had checked out this problem before we were called, and each had determined a different problem and offered to charge the customer thousands of dollars to repair.
It was obvious that the problem was not environmental, as the other contractors had claimed. The crawlspace didn't have a moisture barrier, but even during a good rain, it was dry as a desert in there, except for a line under the duct work. Nothing new you might say, just a return air pressure issue.
The problem was that this one section of subfloor under the hall bathroom was literally growing mushrooms. The wood was so soft I could put my finger through it. There were no plumbing leaks and it was too far from the tub to be overflow.
After a careful look we realized it was the kick-plate vent cut into the bottom of he vanity. Because the HVAC system was condensating so badly, the air it was blowing was wetter than normal. And the old mud pan under the tile was collecting that moisture and keeping the subfloor wet.
With the hard part over, we tore out the bathroom floor, re-framed the rotten wood, moved the vent from under the vanity, and fixed the issue with the HVAC system. And we saved them from spending thousands more dollars with the other guys who wouldn't have even addressed the real issue.
