Baal Habayis
43. Bought house from non-Jew. If a Jew bought a plastered house from a non-Jew, he does not need to scrape a layer off the wall to create a memory of the Churban, as the house was completed permissibly by a non-Jew (שו''ע סי' תק''ס ס''א). However, if the Jew will whitewash or paint the house in the future, when he does so he must leave an unfinished space to remember the Churban (שו''ת ערוגת הבשם קעט).
44. Bought house from Jew. If one bought a house which a Jew lived in but without an unfinished space, the buyer must scrape a layer to create an unfinished space to remember the Churban, as the chiyuv was already in effect for the prior resident (מג''א סק''ד, מ''ב סק''ד).
45. Bought from a Jewish contractor. Some hold that when a Jew buys a finished, plastered house from a Jewish contractor, the contractor does not have a chiyuv to leave an unfinished space, and accordingly, the Jewish buyer also does not have a chiyuv since the house was permissibly completed (שו''ת אג''מ או''ח ח''ג סי' פ''ו). However, if the Jew will paint the house for himself later or if the contractor involves him in choosing the original color, he must leave an unfinished space.
46. Renting from a Jew. If one rents from a Jew, the landlord does not need to leave a space to remember the Churban, as it is not the house he lives in (שו''ת אג''מ שם). Some say the tenant likewise has no chiyuv to leave a space, as it is not his house (שו''ת אג''מ). However, most poskim hold the tenant has a chiyuv to scrape a space on the wall (תורת המועדים, הגריש''א, ארחות רבינו ח''ב עמ' קמ''ח, חזו''א סק''ה). He should first ask the landlord for permission, and the Jewish landlord should not prevent the tenant from fulfilling a halacha in Shulchan Aruch. In the event the tenant anyway must paint the house when his lease is up, he must scrape a space to leave unfinished.
