The Torah states (Devarim 16): “You shall make for yourself a holiday of Sukkot when you gather [the produce] from your granaries and wineries.” Our Sages learned from here (Sukkah 12a) that one should make the Schach out of things gathered from granaries and wineries, i.e. the waste from granaries and wineries, such as straw, hay, twigs, or empty clusters of grapes and the like. Similarly, the book of Nechemia (Chapter 8) states that the leaders of the nation told the Jewish people: “Go out to the mountain and bring olive branches, branches of an oily tree, myrtle branches, palm branches, and branches of a thick tree in order to make Sukkot as it is written.” Our Sages learned from here that in order to be valid, the Schach must meet three requirements: It must grow from the ground, it must be detached from the ground, and it must be something that is not capable of becoming impure (as we have already discussed), similar to the waste of granaries and wineries which grows from the ground, is detached from the ground, and is not capable of becoming impure, for anything which is neither a vessel or a food is incapable of becoming impure. If, for instance, a corpse would come in contact with a palm branch, the palm branch does not become impure. However, if it would come in contact with a wooden vessel, it would become impure, and it is thus invalid for use as Schach (even if the vessel has broken, one may still not use the broken pieces as Schach).
Thus, one may not use any type of metal as Schach, as metal does not grow from the ground. Similarly, one may not use tree branches that are attached to the ground, for only things that are detached from the ground may be used as Schach. Additionally, one may not use foods or vessels (even if they are made from wood) as Schach, for these things are capable of becoming impure. Even if one covers his Sukkah with valid Schach and only places invalid Schach on top of that, the Sukkah is invalid. Therefore, if one builds a valid Sukkah but it is under a neighbor’s balcony, the Sukkah is most certainly invalid.
Paper may not be used as Schach although it is a derivative of wood, since its appearance has changed completely and it is no longer considered something that grew from the ground. Thus, decorations hung from the Schach in order to beautify the Sukkah can very well invalidate the Sukkah, for they are invalid for use as Schach. Therefore, Maran Harav Ovadia Yosef Shlit”a writes that one should take care to hang such decoration within four Tefachim (thirty-two centimeters) of the Schach, for in this way, they are considered insignificant regarding the Schach and they in no way invalidate the Sukkah, even if they are quite large. However, if the decorations droop below four Tefachim of the Schach, there is concern for the invalidation of the Sukkah, as we have explained.
