Growth follows moisture
Mould requires moisture, a food source and time. Building materials such as drywall paper, wood and insulation provide the food source, so moisture and time are the variables that can be controlled.
Where it appears
Enclosed, poorly ventilated and consistently damp areas are the most common locations: behind vanities, inside wall cavities, under flooring and in basements with high humidity.
Correcting the cause
Removing growth without correcting the moisture behind it tends to lead to recurrence, which is why inspection considers both together.
This guide is general information. Conditions vary between properties, so decisions about your building should follow an assessment of the affected areas.