Mishnah for Kelim 9:9

[In the case of] uncleanness among the roof-beams, [with a covering] beneath it thin as thin as garlic-skin, If there is a space within of a cubic handbreadth, everything becomes unclean. If there is not a space of a cubic handbreadth, the uncleanness is considered plugged up. If the uncleanness was visible within the house, in either case the house becomes unclean.