The Mechaber (151:1) brings the prohibition of having kalos rosh in the Bais Haknesses and Bais Hamedrash. Included in this prohibition is sicha b’taila – mundane and idle talk. This also includes sichas chulin for the benefit of one’s livelihood. How much more so one should refrain from speaking lashon hara and the like which are not permissible even outside of the Bais Haknesses. The Zohar speaks very harshly on those who speak sicha b’taila in the Bais Haknesses. This is the cause for the destruction of Batei Knessios and Batei Midrashos and it also delays the geulah.
However it seems that many kehillos are lenient when it comes to speaking sichas chulin in the Bais Haknesses and the Bais Hamedrash. The Mechaber later on (151:12) says that when building a Bais Haknesses a condition may be made that it may be used for other activities which would usually not be permitted to have in a Bais Haknesses. However he says that this only applies after the Bais Haknesses is in a state of destruction and no longer in use. As long as it is still being used the condition won’t help. The Biur Halacha brings the opinion of the Ramban and other Rishonim that this condition works for circumstances of necessity even when the Bais Haknesses is up and running. The Aruch Hashulchan says that many rely on the opinion of the Ramban which is why they are not careful about speaking mundane talk in the Bais Haknesses and Bais Hamedrash. What they are discussing is considered a necessity for them. The Poskim however say that one should not forget that there is still an aron with Sifrei Torah, and care should be taken that whatever is being said is appropriate for such a place.
Many Rabbanim don’t want to rely on the opinion of the Ramban, as the Shulchan Aruch does not rule like him. Therefore at the time of the dedication of their Bais Haknesses they proclaim that it is not a Bais Haknesses rather a meeting place for Talmidei Chachomim and Klal Yisroel. A place where people can gather together, for torah and tefillah. Now they are able to have guests sleep and eat there, use it to bake matzos, and for all other needs of the community. It is called a shteibel, daven shtub – house, or kloiz. They are careful that the sign outside did not say Bais Haknesses. Some are also careful that the inside should not be set up as a regular Bais Haknesses. In the “Grossa Shtub” of the Belzer Rav, the Aron Hakodesh was in the corner and not in the center, and there was also no bima for krias Hatorah.
Reb Moshe zt”l says that those who do this are not fulfilling the mitzvah of “V’asu li Mikdash” which includes the building of a Bais Haknesses. It also lacks the kedusha that is helpful for the teffilos to be accepted by the Ribbono Shel Olam. If there are people who live on top of the Bais Haknesses it is understandable why they would not want it to have the kedusha of a Bais Haknesses, since the Taz is of the opinion that it is prohibited to live on top of a Bais Haknesses.1
Prepared by R’ Avrohom Yehoshua Ziskind
1Sources: Mishna Berura, Piskei Teshuvos, Dirshu