We had a mold issue stemming from a shower vent not connecting to the roof and just dumping humid air into the attic so we wanted to fix that. Found rotten newspaper from the late 40s as insulation mixed with vermiculite under a thin layer of cellulose, which we treated as asbestos and had that professionally removed. Under that found a whole spiderweb of live knob and tube which wasn't connected to any devices, was disconnected from many of its knobs, and was missing insulation in many places while it was draped loosely over some metal plumbing up there.

The project started as a disconnected shower vent causing mold, and ended up with a whole rewire of the lighting and outlet circuits in the house. Wild stuff.

We were also swapping out the breakers for ones up to code since we had messed with the circuits, and one a/gfci breaker just kept tripping. Found a light fixture that had evidentially been sparking away up there for who knows how long.

Feels really good to have had eyes on every box in the house and know that what's there now is leagues safer than what was there before.

One of our friends found that wall severely browned and crisped behind the oven after it was improperly installed for decades, lol. Terrifying wiring mistakes too, the type that make your hair stand on end. They were remodeling after bad water damage and found all sorts of terrible surprises.