Excessive but Isolated Condensation on Bathroom Ceiling

I recently purchased my first condo unit this summer on the top floor of a vintage rehabbed building. When I bought, there were two light brownish superficial water spots on the bathroom ceiling. One circular, with a ceiling blank in the center, and the second more oval but close to the other spot.

When I moved in, I outlined the water marks and left them for 6-8 weeks to confirm they were not getting any larger, and there was no change so I proceeded to paint over them.

This morning I was in a rush and needed to steam a sweater, so ran the shower on hot for 5-10 minutes with the sweater on a hanger in the bathroom. (Not the best practice ever, I know). When I came back into the room there was the expected amount of condensation on the various surfaces, but specifically where the two water spots had been, there was a significant amount of water droplets. For more context, it was also particularly cold here today (30s, maybe low 40s) and my internal apartment temperature hovers within the low to mid 60s.

I am curious if anyone knows what would cause this excess of condensation in those two specific spots? The rest of the ceiling was fine for how long the shower had run. I assume there is unused electrical lines and/or conduit above the ceiling because of the cover plate, but would that be enough to cause such a large temperature shift and create that much condensation? I'm wondering if just not running the shower super hot like that anymore would solve my problem or if I might need to look into a more in depth endeavor to deal with whatever is on the other side of the drywall.

Thanks for any help or insight you can provide!
stefani

Welcome to the site. First, you were running the fan while you were doing this. Mostly I would think air leak to the attic and not enough insulation. If tou can get in the attic, repair vapour bearier and add a little insulation.

Thank you! I am waiting to hear where the entry point into the attic crawlspace is so I can get in there and assess the problem further. In the meantime am reading about vapor barrier installation. Hopefully that will give me a better idea about what's going on. Appreciate the help!

In a rehabbed building should have fire stop walls in the attic, so a fire in in one suite dosn't travel next door, there should be an access in your suite. Have you checked the ceilings in your closets.