The WELL AP notices mold and fungal growth on some indoor walls and ceilings of...

Feature X01 requires that the mechanical system has the capability of maintaining relative humidity between 30% and 60% at all times in all regularly occupied spaces. This is to prevent the growth of mold and other microorganisms that thrive in humid environments. Mold and fungal growth can cause health problems such as allergies, asthma, and infections. The other options are not directly related to the mold and fungal growth, although they may affect other aspects of indoor air quality.

References: = WELL v2 Feature X01: Air Quality Standards