What condition is primarily indicated by black stains on the ceiling?

The presence of black stains on the ceiling typically indicates excessive moisture. This moisture can lead to mold growth, which often presents as dark spots or stains. Conditions causing excess moisture, such as leaks from plumbing or roofing systems, can provide an environment conducive to mold, further exacerbating the staining.

In contrast, dry rot mainly refers to a wood decay caused by specific fungi that thrive in moist conditions, but it does not specifically manifest as ceiling stains. Faulty grading concerns the slope of the land around a building, which can influence drainage but does not directly cause black stains on ceilings. Excessive cellulose debris pertains to the presence of organic materials, like wood, that could attract pests, but it does not produce the visual cue of black stains. Thus, excessive moisture is the key factor associated with the staining observed.