The Gemoroh discusses use of people to form a third wall of a Sukka on Shabbos.
My question is that in Hilchos Sukka, wouldn't this be a problem of Ta'aseh VeLo Min HoOsuy? (i.e. When building a Sukka one must have walls present before putting Sechach on.
What happens if one had a Kosher Sukka, and a wall fell down, and was then put up again - is it Kosher?)
Meir Eliezer Bergman
Dear Meir Eliezer
Thanks for your question, which also bothered me for some time. There are a few possible explanations. One is your suggestion, that if two walls remain standing, there is no problem with rebuilding the third wall. Rav Yoel Shwartz Shlit"a told me that he hasn't seen this issue discussed in the Posskim.
Another possible solution is the ruling of the Rema (635:1) that if a Tefach of the wall near the Sechach was done before the Sechach was placed there, it is permissible to build the rest of the walls after placing the Sechach. Perhaps the case in our Gemara was where the wall fell but the upper Tefach remained in place.
It is also important to point out the opinion of the Bach (among others) who maintains that B'di'eved such a succah is kosher. In our case it might have a Din of B'di'eved.
The Piskei Tshovos 635 ois 2 brings that in such a case it is Muttar, his sources are the Kaf Hachayim 635 s"k 18 (see there also other Deios that Bdieved it is Kosher), and Sefer Pkudas Elozor Orach Chayim Simon 630.