Mold thrives in a hot, humid environment. Unfortunately in the Midwest, this is a common occurrence. Attics and crawlspaces can become a haven for mold growth if the source of water or moisture is not brought under control.In attics, ventilation is the most important factor to prevent mold growth. Installing baffles, ensuring properly ventilated soffits and roof vents will provide adequate ventilation to deter the growth of mold. In the case of a spray-foamed attic, a dehumidifier may be needed to lower the humidity.In a crawl space in the Midwest, standard building practices may even be working against your home. Vents installed in a crawlspace in a humid environment can often make things worse. Heat and humidity coming from the outside will not dry out your crawlspace as it does in drier climates. It is now recommended to encapsulate, dehumidify, and seal off the vents to prevent this infiltration of humidity.