What secondary damage is
Secondary damage is the deterioration that follows the original event: swelling trim, delaminating flooring, corroded fasteners, odour and microbial growth in materials that stayed damp.
Humidity is the usual culprit
Water that evaporates without being removed from the air raises humidity throughout the property and can wet materials well away from the original event.
Monitoring closes the gap
Repeat readings show whether materials are still releasing moisture. Stopping drying based on appearance rather than measurement is the most common cause of secondary problems.
This guide is general information. Conditions vary between properties, so decisions about your building should follow an assessment of the affected areas.