Diagnose and remediate sag in a suspended acoustical ceiling

Steps

1. Diagnose the likely cause before choosing a fix: sustained high humidity or moisture exposure is the most common driver of visible sag in standard mineral-fiber panels, so check for an underlying moisture source (roof leak, uncontrolled ambient humidity, HVAC condensation) rather than only treating the visible symptom.
2. Separately check panel support spacing and installation workmanship (panels seated improperly in the grid, or grid spans exceeding the rating for the specific panel/grid combination) as a distinct mechanical cause from moisture-driven sag.
3. Where humidity is the driver, replace sagged panels with a specifically humidity/sag-resistant rated product line, and confirm the manufacturer's actual tested sag-resistance rating and warranty terms for that product rather than assuming all 'mineral fiber' performs equally.
4. Correct the underlying moisture source (leak repair, humidity control, condensation control) so the same failure doesn't recur after new panels are installed.
5. Where installation/support spacing is the cause, correct grid spacing and support per the manufacturer's and ASTM C636 installation guidance rather than only swapping in new panels.
6. Document the diagnosed root cause before filing a warranty claim, since manufacturer panel warranties commonly exclude sag caused by humidity/moisture exposure beyond the product's stated rating.