Roof fall occurred in XC13 on the 1st main W off main N between entry 7 and entry 8. The fall is 17,000' outby the loading point. It is between two overcasts providing a limited intake aircourse to two seals. It is approximately 19.5'Wx75""Lx8'H. No injuries/equipment involved. 1 corner of 1 overcast was damaged which allowed limited intake air to cross with Unit 5 intake air.