A Sukkah that was built for the sake of the Mitzvah and was not used as a dwelling place during the year:[1]
A Sukkah that was built for the sake of the festival [for the purpose of fulfilling the Mitzvah] is valid even if it was built in the beginning of the year. It does not require any modification. [Thus, if one never took down the previous year’s Sukkah, it may be used for the current Sukkos holiday without needing any modification, as explained in Q&A.]
[1] Admur 636:1; Michaber 636:1; Mishneh Sukkah 9a
Other opinions: Some Poskim rule that even if the Sukkah was built for the sake of the Mitzvah, if it was built prior to 30 days before Sukkos one must renew some of the Sechach before Sukkos, as recorded in D. [Bach 636; Birkeiy Yosef 636:2]