Is there a difference if one says Tachanun with a minyan or without a minyan, or if one says it when there is a Sefer Torah or not? The qustion was asked as a response to the Shiur https://www.yeshiva.co/midrash/17772

Shalom, Thank you for your question. Yes, there are differences between saying the Tachanun prayer with a minyan and without one. Connected to the Tachanun prayer one also recites the Vidui and 13 attributes of mercy. Different communities say these parts with different frequencies – the Sepharidim say them with every Tachanun, while the Ashkanazim outside of Israel tend not to say them at all. Some say them only at the morning service on Monday and Thursday, and some say them every morning and mincha. However, all agree that the 13 attributes of mercy can only be said with a minyan. Without a minyan one may read them as verses from the Torah if one knows how to recite them with the tune of the Torah reading, or leave them out entirely. But, apart from this, there are no differences between Tachanun with or without a minyan. As to saying Tachanun where there is a Sefer Torah or not – this effects whether a person “falls on their face” (nefilat apaiyim). There is a paragraph of the Tachanun that is said with the head resting on one’s arm (the Sephardim do not have this practice). Whether one does this or rather says the paragraph just sitting up, depends on whether there is a Sefer Torah in the room. If there is no Sefer Torah one says the paragraph without leaning down on their arm, just sitting up. If one is in a room with a Sefer Torah, the leaning is done while saying the paragraph. There is much discussion as to what, and where, exactly is defined as a place with a Sefer Torah. The custom in Jerusalem is to lean even in a place with no Sefer, as the whole city is on a special level of holiness. Some do this only in the old city, and some say this applies to the whole city of modern day Jerusalem. Some opinions believe that even a room with printed holy books suffices to allow one to lean. There is also debate as to the rooms adjoining the main shule where the Sefer Torah is housed. As you can see there are various opinions which are resolved differently in different communities. In general you should follow the local custom – but if that is difficult for you to ascertain, and if you have a particular situation, please feel free to write to us again with further questions. Blessings.