Question: How and why does mold get started growing?

ANSWER:  Mold and mold spores are present as a natural part of life on earth.  As long as a habitat for mold growth is not inside a building then this natural mold is not an immediate threat to our indoor air quality. 

Mold needs 3 things to survive: moisture, food source, and a surface to grow on.  If moisture is allowed to go where it is not suppose to go the process of mold growth can start.  An example is a roof leak that allows water to enter the attic and onto the ceiling or down the walls of the structure.  This water dampens the drywall, wood, insulation and other building materials, all of which can act as food for mold to feed on.  These building materials can also act as the surface for mold to grown on.  Now the habitat is ready to grow.