Leaks and water intrusion
Plumbing leaks, roof leaks, foundation moisture and other water entry can wet building materials long enough for mold to grow.
Condensation and humidity
Condensation on windows, pipes or cool surfaces can create localized dampness. EPA recommends keeping indoor humidity below 60 percent when possible, ideally in the 30 to 50 percent range.
Wet materials after an incident
Carpet, drywall, insulation, wood and furnishings that remain damp after a spill or water event may support mold growth.