Siman 636
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א סֻכָּה יְשָׁנָה, דְּהַיְנוּ שֶׁעֲשָׂאָהּ קֹדֶם שֶׁיִּכָּנְסוּ שְׁלֹשִׁים יוֹם שֶׁלִּפְנֵי הֶחָג, כְּשֵׁרָה וּבִלְבַד שֶׁיְּחַדֵּשׁ בָּהּ דָּבָר עַתָּה בְּגוּפָה לְשֵׁם הֶחָג, וַאֲפִלּוּ בְּטֶפַח עַל טֶפַח סַגֵּי אִם הוּא בְּמָקוֹם אֶחָד; וְאִם הַחִדּוּשׁ עַל פְּנֵי כֻּלָּהּ, סַגֵּי אֲפִלּוּ כָּל דְּהוּ; וְאִם עֲשָׂאָהּ לְשֵׁם הֶחָג, אֲפִלּוּ מִתְּחִלַּת הַשָּׁנָה, כְּשֵׁרָה בְּלֹא חִדּוּשׁ.
1 The Law of an Old Sukkah, 2 Seifim: An old sukkah — i.e., one that was made more than 30 days before Sukkos — is valid provided something new was done to it for the sake of the festival (See Sukkah 9a). For this, even a handbreadth by a handbreadth is sufficient if it is in one place and if the new thing was done for all the Sukkah. And if it was done for the sake of the festival, even if it was done at the beginning of the year, it is valid without anything new.
ב יוֹצֵר כְּלֵי חֶרֶשׂ שֶׁיֵּשׁ לוֹ ב' סֻכּוֹת זוֹ לְפָנִים מִזּוֹ וְעוֹשֶׂה קְדֵרוֹתָיו בַּפְּנִימִית וּמוֹכְרָם בַּחִיצוֹנָה, הַפְּנִימִית אֵינוֹ יוֹצֵא בָּהּ יְדֵי סֻכָּה כֵּיוָן שֶׁהִיא דִּירָתוֹ כָּל הַשָּׁנָה אֵינוֹ נִכָּר שֶׁדָּר בָּהּ לְשֵׁם מִצְוָה; וְהַחִיצוֹנָה יוֹצֵא בָּהּ, שֶׁהֲרֵי אֵינוֹ דָּר בָּהּ כָּל הַשָּׁנָה.
2 [The following laws apply with regard to] a potter [whose workplace is comprised] of two [adjoining] sukkos, one of which gives access to the other, and he fashions his pots in the inner [sukkah] and sells them in the outer [sukkah]. Though the inner sukkah was built for shade, he does not fulfill [the obligation to dwell] in the sukkah with it because it serves as his dwelling throughout the year. Since he eats, sleeps, and performs most of his activities there, it would not be evident [during the festival] that he is now doing these things for the sake of the mitzvah. He may, however, fulfill his obligation using the outer [sukkah], for he does not dwell in it throughout the year.