I am trying to find out what is causing a large area of my great room ceiling to turn black - it looks like mold - We had a new roof installed two years ago. Our area has not had a lot of rain this summer and the air conditioner has run all summer. The problem has occurred in the last three months. The house is a modular and the area is just below where the halves join. Could there be a leak? There are no water spots only this black fungus or mold on the textured ceiling.