We sold our home and have been renting because construction on our new apartment is not complete. Now, it is basically ready, but lacks a Tofes 4 (municipal permission to inhabit). If we get the Tofes 4 during the Nine Days, is it permitted to move in then? Answer:
Classical sources do not discuss entering an apartment during the Nine Days, but building then. The gemara (Yevamot 43b) requires one to "lessen building activities" during the Nine Days, without specifying. In a parallel context, the gemara (Ta’anit 14b) says to not build a "house of simcha" on a fast day and gives as an example building a house for a chatan, implying that most building is permitted. In contrast, the Yerushalmi (Ta’anit 4:6) writes that it is permitted to build when there is concern that a wall will collapse, implying that most building is forbidden. The Shulchan Aruch (Orach Chayim 551:2) brings both extreme rulings; the Mishna Berura (ad loc. 12) follows the Magen Avraham and Ran, who say that any unnecessary building, for nonessential expansion/enhancement, is forbidden.
Our understanding (see Bemareh Habazak III:60) is that when something is too simcha-related to be permitted to build in the Nine Days, one should not move into it either (Levushei Mordechai I:101 disputes this thesis). It should also be at least as problematic as wearing a new article of clothing (Levushei Mordechai disputes this too), which is forbidden on grounds of simcha (Rama, OC 551:6).
431 - Geniza for Parts of a Pasuk
432 - Moving into a Home During the Nine Days
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Let us, therefore, investigate whether building would have been permitted. The Mishna Berura (ibid.) permits to build when it is needed to enable normal living conditions. In your case, this is not grounds for leniency if your present rental setup is satisfactory.
However, the Mishna Berura (551:13) permits building needed to prevent a financial loss, similar, although less dramatic, to the Yerushalmi’s case of a possibly collapsing wall. Finishing up the building to receive the building’s Tofes 4 is certainly justified, as even a minor missing detail can hold up a building-full of families for weeks, causing large losses of money and hardship. Is paying several days of rent enough of a justification? In a parallel case of buying a car during the Nine Days, Rav Moshe Feinstein (Igrot Moshe, OC III:80) allows it when needed for work (it is unclear what his assumptions were regarding the person’s alternatives: no job, renting, using taxis?) In your case, it depends greatly on the individual family and its financial situation. In borderline cases, there is logic to allowing moving in during the beginning of Av but not during the week in which Tisha B’av falls (Bemareh Habazak ibid.).
There is another issue – the beracha upon entering the house. The Shulchan Aruch (OC 551:17) says that one should refrain from reciting Shehecheyanu during the Three Weeks because the time is one we are not happy about. Many assume that one should recite Shehecheyanu upon entering a new house (see Shulchan Aruch, OC 223:3). The Levushei Mordechai (ibid.), whom we cited as being very lenient on building, forbids entering the home due to inability to recite Shehecheyanu. Rav Moshe Feinstein (ibid.) ruled, that in case of need, one can get the car during the Nine Days and recite Shehecheyanu after Tisha B’av; that logic applies here too. In Bemareh Habazak (ibid.), we accepted the Bi’ur Halacha (to 223:3) that when the homeowner has a wife and children benefitting from the house, the beracha to make is Hatov V’hameitiv (see more in Living the Halachic Process V, D:18), rather than Shehecheyanu. Since it does not mention "this time," it is permitted in Av.
Another factor in play here is the concern that major projects undertaken during this period will be lacking in good mazal (see Ta’anit 29b). We are not experts on the rules of mazal. We suggest to consider the psychological element as well – a believing Jew is sometimes uneasy and/or regretful, short and perhaps long-term, about projects he did in the Nine Days, and it is wise to consider that feeling as well.