How can a roof leak be investigated when the attic is inaccessible?
Distinguish the evidence available
If the stain appears during wind-driven rain, record the direction and duration of the weather and the affected room. Ask the investigator to compare roof penetrations, wall intersections and openings above that location. The timing narrows the investigation; it does not prove a particular flashing joint failed.
If moisture appears during cold weather without a clear rain event, include condensation in the investigation. Air leakage, insulation and the actual vented or unvented roof design need consideration before anyone adds vents or seals an arbitrary opening.
If moisture continues after a repair, request a documented reassessment rather than another unexplained surface patch. The contractor should state whether the remaining uncertainty requires a different specialist, a targeted opening or another controlled inspection method. Any opening needs an agreed location, purpose and restoration scope.