Midrasch zu Wajikra 14:41

2) "and they shall remove": This teaches us that both of them (i.e., the owner of the affected house and his neighbor, who shares the wall) remove — whence they said "Woe to the wicked one and woe to his neighbor!" Both remove, both scrape (viz. Vayikra 14:41), both bring (new) stones. I might think that if the wall adjoined the atmosphere (of his neighbor's property, but was not common to both of their houses) both of them should do the removal; it is, therefore, written (Vayikra 14:43) "after he removed the stones." How is this to be understood? A wall between him and his neighbor, both remove; a wall adjoining the atmosphere, he himself removes.

5) (Vayikra 14:41) ("And the house he shall scrape from inside roundabout, and they shall spill the mortar scrapings outside the city into an unclean place.") "And the house he shall scrape": I might think from inside and from outside; it is, therefore, written "from inside." If "from inside," I might think from the ground and from the walls; it is, therefore, written "roundabout" — only the area roundabout the plague-spot.

6) "and they shall spill … which they have scraped off": I might think that pebbles (are included); it is, therefore, written "mortar." If "mortar," I might think that even what fell of itself (is included); it is, therefore, written "which they have scraped off." If both verses were not written, we would not know the halachah.