Midrash su Levitico 14:45

1) (Vayikra 14:45) "Then he shall raze the house — its stones, its wood, and all the mortar of the house": We are hereby taught that a house is not subject to plague-spot uncleanliness unless there be in it stones, wood, and mortar....

2) How many stones (in total) must be in it (on all sides to make it subject to tumah)? R. Yishmael says four (one on each side). R. Akiva says eight (viz. Section 6:4). For R. Yishmael says: Until there appear two garisin on two stones or on one stone. R. Akiva says: Until there appear two garisin on two stones, and not on one stone. R. Elazar says: Until there appear two garisin on two stones on two walls in one corner, its length two garisin, and its width a garis.

3) (if the plague is in) his stones, and his mortar, and his wood: and not, (if the wall were jointly owned), in those of his neighbor. "his stones": We are hereby taught (that in a case of joint ownership) he planes (his portion from that of his neighbor) and removes his stones. "its stones": all the stones with which the house was built (and not those that were superadded to it after it was built). "its wood": all the wood with which the house was built. "its stones": and not those of the attic. "its wood": and not those of the attic. "the mortar of the house": and not that of the attic — whence it was ruled: If a plague-spot appeared in the house, he places the beams in the attic. If it appeared in the attic, he places its beams in the house. "its stones": and not stones which were superadded to it after it was built. "the mortar of the house": and not mortar that fell off from it (before the house was razed). "and he shall take them (the stones) outside the city to an unclean place": If this is already written in respect to removing (the stones, viz. Vayikra 14:40), why need it be written in respect to razing? And if it is written in respect to razing, why need it be written in respect to removing? Because there obtains with removing what does not obtain with razing, and because there obtains with razing what does not obtain with removing. With removing, the stone on a side (common to that of his neighbor) — he removes the whole, (even that of his neighbor [viz. Chapter 4:2]), and when he razes, he razes (only) what is his and leaves that of his neighbor; and in razing, he razes both the stones with a plague-spot and those without a plague-spot. So that because there obtains with removing what does not obtain with razing, and with razing, what does not obtain with removing, both removing and razing must be written.