While moving out of my apartment, I discovered a staggering amount of black mold behind my furniture. The mold was only on walls facing outside (ie no mold on walls with rooms on both sides) and didn’t creep up to be seen outside the borders of my furniture. I’ve never regularly moved my furniture for cleaning, and I’ve never experienced this at another home. I’ve lived in this home for 2.5 years and the furniture affected was in place between 1 and 2.5 years. The home is a quad-plex apartment building built in the 40s and definitely doesn’t have the best ventilation. My unit is on the second floor. The mold was the worst in the bedroom, where the two exterior facing walls were basically lined with furniture. The mold went from the top of the baseboard up about two feet vertically and 6-8 feet horizontally in the worst spot. Again, all of this was shielded by furniture for god knows how long. The home layout is kind of l-shaped with the bathroom as the corner between the living room and bedroom. I can’t think of anything I’ve done here to promote excess moisture or humidity. What I’m wondering is whether this was likely to be a preexisting issue or something I inadvertently caused. I cleaned most of it with Tilex and Clorox. I also took the photo above for records and have two witnesses to the worst of it. The photo above is the last place I found it, in my closet. Luckily I didn’t lose too many belongings, but some furniture has to be treated so I don’t bring it into my new place. Any insight is greatly appreciated in case I have to chew out the rental company.