ok? I'm adding a dropped ceiling in my bathroom as there is an outside roof just above my ceiling. i noticed some condensation on the inside of the outside wall inside the void. There is no ventilation and not a lot of air in the void. void is only 200mm deep. do you think i need ventilation. I was thinking of drilling a series of holes in for ventilation but what diameter should they be and how many? void is 2.4x 1.5x 0.2 metre any help appreciated.s. Would i be able to get away with just stuffing the void completely with insulation? thanks in advance.