Roofs That Block Tuma
18. Any roof (as defined above) that is attached permanently to the ground blocks tuma from spreading through it. If a corpse is lying under such a roof, a kohen may stand above it; and vice versa.
19. Therefore, a kohen may remain in an apartment directly above or below an apartment where there is a dead person, provided there is no opening connecting the two apartments, such as an overhang protruding over the windows of both apartments or a hallway connecting them.
20. An object that is not susceptible to tuma and is also not a vessel — for example, a plank of wood — blocks tuma even when it is not connected to the ground. However, people, utensils, and anything susceptible to tuma are not considered a “roof” that blocks the spreading of tuma but a “roof” that causes tuma to spread. Thus, an umbrella spreads tuma beneath it, and does not block tuma from spreading above it. The tuma spreads above and below the whole umbrella and reaches even areas that are not directly above the corpse.
21. Even if a roof is merely supported by a utensil or person, it cannot block tuma. Therefore, if a person holds a plank of wood (even though it is not a utensil) over a corpse, the plank will not block the tuma from spreading, but will spread tuma just like the umbrella mentioned above.
When Utensils Block Tuma
22. Utensils designed to be used when attached to the ground block tuma from passing through them.
23. A container with a capacity of forty se’ah, the minimal size of a mikve (approximately seventy gallons), blocks tuma from entering it provided it is not made of metal and has no wheels.
24. If a utensil that is not susceptible to tuma touches the side of a structure that blocks tuma, the utensil also blocks tuma like the structure next to it.
25. Cloth that is spread permanently to serve as a tent and is connected to the ground blocks tuma. There is a dispute whether this ruling also applies to tents of wool or linen.
Future Exits (Sof Tuma Latzeis)
26. When the doors and windows of a room containing human remains are all closed, the openings through which the body will eventually be removed are considered as if they are already open. Therefore, a kohen is not permitted to be in a room through which a corpse will be removed, nor may he remain in any room that is open to the rooms through which the corpse will pass.
27. If it has not been decided through which opening the body will be removed, tuma spreads through every door and window fitting for the corpse’s removal.
28. Any closed opening less than four tefachim high and four tefachim wide is not considered fitting to remove human remains.
29. If even one door or window is open, the closed doors and windows will block tuma from spreading through them, since we assume that the body will most likely be removed through the open exit.
30. There is a difference of opinion as to whether this tuma of “future exits” is a Scriptural or a rabbinic decree.
31. Kohanim should therefore not go through places with the above problems, even in order to fulfill a mitzva.