:confused: Once the weather gets warm around 70 degrees and sunny, the south west side of the house starts to smell, around 2 in the afternoon (once the sun is no longer shining on the house). It smells similar to cat urine. We have had mold tests (they came out negative), we have cut into the walls and fire place (no water damage, smell isn't present), the smell isn't in the attic or basement, we have had a plumber in to do a smoke and peppermint test (he wouldn't do the test because the area that smelled didn't have pipes, and he didn't i.d. the smell as plumbing related). A few siding companies have said that maybe the smell is wet insolation. When the aluminum siding gets hot, it heats up the wet siding and puts off the smell. Is this possible? What else could you think this smell could be?

Have you loked around to see if a small rodent may have died in walls?

MOLD - it grows when it turns warm. That's what you smell.