Why is my ceiling wet but no leak?

Three non-roof causes account for most of these in the Myrtle Beach area. HVAC condensation tops the list. Our summers hit 85 percent humidity, and an uninsulated attic duct sweats enough water to soak drywall in a week. AC condensate drain backup is second; the PVC line clogs with algae and overflows from the air handler into the ceiling below. Third is attic humidity from blocked soffit vents, common when new insulation gets stuffed against the eaves. A coastal-specific one: salt-air corrosion pits copper plumbing pinholes in slab homes within a mile of the ocean, dripping into ceilings on a lower story. Check your attic in daylight before you call a roofer.