People call me to evaluate many things. Arriving at the house, an older home, I did a little interview to see what it is that they were trying to describe over the phone.
After the "interview," I always go to the complaint area first. This was in the basement. From there I knew where the problem was originating. So I went outside to see why.
When I saw this gap under the sliding door to the deck, I suspected long-term moisture intrusion and was not surprised, when in the basement, to have heard,
"This is the room that smells bad."
Years ago this newer door had been installed in the rear corner of the house without a proper seal underneath.
When the vinyl siding was hung, perhaps at the same time, no correction was made!
And it is easy to see that the deck was not level, leaving exposed what you see here, so this gap was known about by some "professional" contracting company. They never bothered to correct it.
Next you'll ask me if I was shocked.
So, is that door-wide gap letting water in?
The left image is of the lower basement corner under that spot.
The right image is of the basement ceiling under that spot.
Cooler locations, and therefore probably wetter, are indicated by lavender, blue and purple.
The moisture meter registered almost 30% moisture. Yep, that's wet!
So, obviously this moisture, slowly getting in, is feeding microbial growth inside the ceiling and wall below that door.
Hence the smell.
So, going to evaluate one thing, I was able to discover the source and an issue previously unknown to this homeowner.
My recommendation: when looking for the cause for one condition, often I find it's related to something else not entirely understood or known to the homeowner. But when the two are put together the problem makes total sense. People sometimes think I'm a genius when I figure stuff like this out. No, not really. I started bowling when I was eight years old, and I am really good at addition!