Midrasch zu Wajikra 14:53

15) (Vayikra 14:53) ("And he shall send the living bird outside the city over the face of the field, and he shall make atonement for the house, and it shall be clean.") "And he shall send the living bird outside the city": R. Yossi Haglili says: a bird that lives outside the city. Which is that? A free bird (i.e., one which lives anywhere).

15) "and he shall make atonement for the house and it shall be clean.": If this (procedure with the birds) is written in respect to a leper, why must it be written in respect to houses? And if it is written in respect to houses, why must it be written in respect to a leper? Because there obtains with houses what does not obtain with a leper, and with a leper what does not obtain with houses. A leper requires an offering and a house does not require an offering. A leper has cleansing from his tumah and a house has no cleansing from its tumah, (but must be razed). So that because there obtains with a leper what does not obtain with houses, and with houses what does not obtain with a leper, both a leper and houses must be written.