It says in SA Siman 638 that one may make a tanai on the "noi sukkah" in order he should be able to use it during the chag and that it won't become muktzeh l'mitzvaso. In theory could one do this with the scach as well (in order that it won't become muktzeh and the person will be able to be m'taltel without a shinui.) If not what is the reason why?
Yehoshua, Yerushalayim, Eretz Yisrael
Dear Yehoshua,
The Tur and the Rema both tell us that the Tenai that you are referring to only works on the Noi Sukkah but not on the Sechach or Defanos of the Sukkah. What is the difference? The Mishnah Berurah explains: the Noi Sukkah you could use Bein haShemashos at the beginning of the Chag. You could eat the dates you are hanging up, etc. Therefore it is possible to declare that you are not separating yourself from the Noi Sukkah for the whole Bein haShemashos. But the Sechach and the Defanos cannot be touched during Bein haShemshos because of the prohibition of Stiras Ohel. Therefore, one cannot make the statement: "I am not separating myself from the Sechach for the whole Bein haShemshos", and as a result the Sechach because Muktzah l'Mitvaso for the whole eight or nine days.
All the best,
Yonasan Sigler
This is not a Psak Halachah