Hello group. New guy here. I'll try to detail as much as I can about the issue. Yesterday the wife noticed some green mold growing in our spare bedroom that we use primarily for storage. The ceiling had 2 wet spots on the tile, close to the corner of where the exterior walls meet. The wall paneling has buckled but I'll deal with that later. The ceiling tile is the 12x12 tongue in groove stuff you staple to the boards that will hold it.
Anyway here is the layout. Seems to be sheet rock ceiling, then the tile. Then new boards fastened to that with new tile over that. Styrofoam panels were put in between the boards as insulation.
I tore out about a 1/4 of the tiles in the room, around that corner and area of wet spots and found some condensation. I cannot remember definitely whether the area with the condensation had any Styrofoam under it nor not.
This room is just storage for us. We've been In the home 3 years now and have had no issues until now. We keep the door shut. It does not get much heat and is usually cold when we do enter. We have a pellet stove in the living room that will heat the whole house if we leave doors open. Roof was new in October 2018 and I've verified no leaks and no sign of water.
What gives? I need to replace the ceiling now and probably wall panels. But I want to fix this to avoid doing it agsin.

 

So you say you have a low conditioned room, assume there is no bathroom attached that would be dumping a lot of warm moist air, so that sort of rules out condensation.

I dont follow all the layers and foam, is there an attic above? It sure sounds like a water leak!

 

The bathroom is next to this room. The bathroom fan vent pipe is easily 10-12 feet from the condensation and there are no signs anywhere other than where I've noted. I did a thorough walk through of the entire attic today with extra focus on this area above the spot in question.. No sign of water leaking anywhere in the attic.

I'm wondering if I have inadequate insulation in that particular area?!
The attic- this used to be a flat roof at one time. A gable roof was built over it at some point.
What is now the attic floor is boards covered in something like tar/tar paper.
Still no sign of any water leaks up there. Nothing is wet or damp.

The sheetrock on the ceiling of the room where the condensation was found appears to have been painted. And it's clearly condensation and not a leak. I'm positive of this.

I also don't get the layers of ceiling tile. But people do strange things!