Siman 636

We learned in a Mishna (9a): An old sukkah—Beit Hillel declare it kosher. And what is an old sukkah? Any that he made thirty days before the festival. But if he made it for the sake of the festival, even from the beginning of the year—it is kosher. That is to say: for anyone who makes it before the thirty days adjacent to the festival—presumably he does not make it for the sake of the festival. Nevertheless, it is kosher, for we do not require a sukkah to be made lishmah, as I wrote in the previous siman. And this is what this Mishna teaches us: that we do not require a sukkah to be made lishmah. And in the Yerushalmi it says that nevertheless one must innovate something in it for the sake of the sukkah of the mitzvah: either the span of a tefach, or any small amount across its entirety. But if he made it for the sake of the festival—he does not need to innovate anything in it, even if he made it from the beginning of the year. (See Chayei Adam, who wrote that if he made it for the sake of the festival for the following year—he must innovate something in it. And his words are astonishing.)

And certainly, this requirement to innovate something within it is not by Torah law. And even by rabbinic law, this is not a necessity, but merely a beautification (Ran and R.Y.V. and Magen Avraham). And the proof: from the fact that they did not mention this in the Gemara. Furthermore, regarding the sukkot of Ganevach and Rekabash mentioned in the previous siman, they did not mention this. However, for the choice fulfillment of the mitzvah, it is obvious that there too one should innovate something: either a tefach by a tefach in one place, or a small amount across its entirety. And the innovation is simply that he should lift a bit of the sechach of this measure, and return and place it for the sake of the mitzvah of sukkah (Taz and Magen Avraham).

A potter who has two sukkot, one inside the other, and he makes his pots in the inner one and sells them in the outer one—he does not fulfill his obligation of sukkah in the inner one, since it is his dwelling all year, it is not evident that he dwells in it for the sake of the mitzvah. As I have written, regarding one's year-round house—one does not fulfill the obligation of the mitzvah of sukkah in it. But in the outer one—he fulfills his obligation in it, since he does not dwell in it all year.