We already discussed tzara’as affecting people and garments (Mitzvos #169 and #172, respectively), but tzara’as could also affect houses, though only in the land of Israel. If a house showed signs of tzara’as – green or red marks – then the owner had to tell a kohein, who would investigate. If the kohein ordered the house quarantined, he would return a week later. If the infected area had spread, the kohein would order the affected stones removed and discarded, while the wall of the house would be re-plastered.
If the signs of tzara’as did not return, the house would be purified using cedar, hyssop, crimson thread and birds, as in the case of people (see Mitzvah #173). If the tzara’as came back, the house would be condemned. The materials of the infected house had to be carted away and discarded outside the city.
There are two reasons for this mitzvah. The first is similar to the reason for tzara’as in garments: God is merciful, so He sends the message of tzara’as, i.e., that a person should clean up his act, through a person’s possessions before He strikes that person in his body. The supernatural appearance of tzara’as in one’s house was meant to serve as a wake-up call.
The second reason is a unique historical event. Rashi on 14:34 cites the Midrash in Vayikra Rabbah that the Amorites had hidden their gold in the walls. When they were driven out and the Israelites moved in, the gold remained hidden. God caused tzara’as to manifest in houses where these treasures were stashed – even though the owners may not have spoken gossip, the typical cause of tzara’as. In this manner, the houses were razed and the gold was revealed. This is a perfect example of “all that God does, He does for the good” (Brachos 60b). At first, a person might curse his luck that his house was condemned, but his tune would quickly change when the gold was revealed!
This mitzvah applied to both men and women in Israel when there were kohanim trained to recognize tzara’as. It is detailed in the Mishna in the twelfth chapter of tractate Negaim. This mitzvah is codified in the Mishneh Torah in the fourteenth chapter of Hilchos Tumas Tzara’as and it is #103 of the 248 positive mitzvos in the Rambam’s Sefer HaMitzvos.