From the TOH ****** EDITORS Inbox:
For some time now a spot in my carpet gets damp and stays damp for long periods of time. I have explored under the spot from the crawl space and find no sign of moisture, I have drilled through the floor and located the center of the spot, cut the vapor barrier and put my hand thru and the top of the insulation is dry. Have you ever had a similar problem? Any suggestions? I am getting ready to replace the carpet of perhaps put a wood or laminate floor in that area and more.
Thanks for your help.
Isaac F. Bowman
Note: This link has been sent to Isaac and he will be checking here for your answers.
Re: Wet spot
Perchance is this ominous wet spot adjacent to the wet wall of the shower, toilet, vanity, or any other water source such as a refrigerator water supply or AC condensation line?
I've had several instances where a tub surround was leaking, the water followed the framing and wall until it reached the hallway floor, about 3 feet away. There was no sign of water anywhere else but the carpet in the hallway.
Another source could be an interior AC/furnace closet. I've also had instances where the weep tube for the AC unit had become clogged and backed up into the house.
In my own house the overflow of the upstairs bathtub failed so that whenever someone took a bath and splashed water around the overflow, it would leak into the ceiling cavity of the bathroom below, travel over to the wall and down to the downstairs floor. This was a fun one to find because the wet spots were no where near obvious water spots. The ceiling felt a little damp, which indicated the problem was the bathtub above, sure enough the overflow gasket had deteriorated and fail.
What is the topography of the house around the area in question and what are the nearest water sources, condensation lines, etc.