1,171. The Walls of the Succah
Hilchos Shofar, Succah v’Lulav 4:15
Let’s say that the interior height of a succah was less than ten handbreadths tall (about 30”) and one dug into the ground in order to create a height of ten handbreadths. In such a case, if there are three handbreadths (about 9”) from the hole to the succah wall, it is invalid; less than that is valid. This is because any distance of less than three handbreadths is considered bridged, as has been explained in Hilchos Shabbos.
Hilchos Shofar, Succah v’Lulav 4:16
The walls of a succah may be made from any material – even living beings – so long as they form a barrier. One may eat, drink and sleep in a succah by using his friend as a wall, even on yom tov. This latter part only applies when the person being used as a wall is not aware of it; it is prohibited to create a wall on yom tov by using a person who is aware of it. It is permitted to do so on the other days of Succos. Similarly, one may create a fourth wall out of utensils on yom tov but one may not create a third wall out of utensils on yom tov. This is because adding a third wall renders a succah fit for use and one is not permitted to make a tent – not even a temporary tent – on yom tov.