A board is placed on top of a new oven and extends a handbreadth on all sides: if there is tumah beneath [the board], utensils above it remain tahor. If there is tumah above [the board], utensils beneath it remain tahor. [However, in the case of] an old oven, the oven becomes tamei. R’ Yochanan ben Nuri rules it tahor. [If the board] is placed on top of two ovens [and] there is tumah between them, they become tamei. R’ Yochanan ben Nuri declares [them] tahor.

A perforated slab is placed on top of an oven whose opening is sealed. If there is tumah beneath or above [the slab], everything becomes tamei; [except for] what is directly above the inside of the oven, which remains tahor. [If there is] tumah above the inside of the oven, [whatever is] directly above [the tumah], until the sky, becomes tamei.