How do you know if mold is behind a wall?

Hidden mold is most often suspected when there’s a history of leaks, elevated moisture, staining, musty odor, or recurring humidity/condensation—especially in areas with limited airflow. A good investigation typically starts with moisture diagnostics and building science indicators (not just “sniff tests”). Depending on access and goals, the next steps may include targeted sampling or a controlled opening plan coordinated with the appropriate contractor.