An unplanned roof fall was discovered in #6 entry of the 4A Belt Mains tow breaks outby spad #1104, between break 47 and 48 (did not extend into intersections). Fall was approximately 55 ft long, 18 ft wide and up to 15 ft high. Travelway from the track to section goes through break 47. No injuries, entrapment or equipment involved. No ventilation affected.