Did you by any chance add some new fabric to your house? One of my females, Yodie, HATES a certain table cloth that I put over an occasional table. I'd no sooner take it out of the dryer, put it on that table and she'd spray on it. She did the same thing w/a bathroom rug. I finally gave up and got rid of those items and the peeing stopped. Cats are so sensitive to smell and that's their way of telling you that they don't like something. Could there be something in the basement that you've seen them sniff that tells you it's unpleasant to them? If the bad behavior spread to the upstairs, there may be something there, too. One of my males, Coco, sprayed on my silk draperies in the dining room. I just hung them and w/in 5 minutes he sprayed on them. I don't know if it was the newness of the fabric or what but once I had them cleaned, he never did it again.

I will say, though, that I have another male, Specs, who started a pee war between himself and my now deceased other male, Boo, and it got so bad that I had to go the medication route. I tried Feliway and it didn't work for them. That's a last resort, though. Give Feliway a try. Others here on PT have seen success w/it. It's a pheromone that comes in a plug-in diffuser or a spray. Give it a whirl.

Oh, and welcome to Pet Talk!