Sukkos

1. The schach must be made of something that grows from the ground and is not “mekabel tumah”.
2. The halacha concerning types of covering which are invalid as schach is:
a. If there is a section of 4 tfochim (approx. 13 inches) which runs across the width or length of the sukka it breaks the sukka into two parts.
b. If it does not run across, one should still not eat or sleep under that amount of “schach posul”.
c. If it is less than 4 tfochim, the Shulchan Aruch feels one may even sleep under it. The Mishna Brura quotes opinions that only less than 3 tfochim (approx. 9 inches) would be permissable to sleep under.
d. If the invalid schach is on the side of the sukka and there is a large enough area covered with good schach, then the sukka as a whole is valid even if there is up to six feet of schach posul. The reason for this is we imagine the wall on that side as being bent up until the good schach. If there are three walls without it, then certainly the sukka is valid.
3. This brings us to a prevalent problem of a sukka under an overhang or gutter of a roof. Based upon the previous rules we conclude: if the overhang is less than 9 inches one could even eat under that part of the sukka. If it is more than 9 inches it does not invalidate the sukka and can act as a third or fourth wall until 6 feet. An overhang of more than that is considered separated from the sukka and one must have three walls in addition to that one to have a kasher sukka.
4. If the whole sukka was the minimum size of a sukka (which is about 28 inches wide and long), and if the amount of overhang was less than 9 inches, then the overhang could join together to create the necessary 28 inches and one may even sleep or eat under it.