1 - Guidelines to Kosher "S'chach" 2 - More Sun than Shade 3 - Some Laws concerning S'chach 4 - The Structure of a Kosher Succah 5 - A Succah under a House or a Tree 6 - Sitting under the Shade of the Succah 1 - Guidelines to Kosher "S'chach"
In order for the S'chach (roofing) of a Succah to be Halachically acceptable it must fulfill three basic conditions. The first condition is that the material from which the S'chach is made be earth-grown, from the plant-kingdom, like branches or bushes. Metal, lead, and plastic, although they originate from the earth, are unacceptable for S'chach because they are nonliving.
The second condition is that this earth-grown substance be detached from its source; so long as the branches are still attached to the ground, they are not acceptable for S'chach. Therefore, it is forbidden to build a Succah under a tree, using the tree's branches as S'chach.
The third condition is that the S'chach not be made from anything that can receive impurity; generally speaking, containers, clothing, chairs, and beds are the objects capable of receiving impurity. As a rule, any natural product that in its unaffected form cannot receive impurity, becomes capable of receiving impurity after it has been manipulated and made acceptable for the use of man; with its elevation to the status of a significant utensil it becomes suited for receiving impurity. From this point onward, should it come into contact with a corpse or any other object that causes impurity, the utensil becomes impure. From the moment that the wood becomes capable of receiving impurity, it becomes unacceptable for S'chach.
Therefore, it is permissible to roof a Succah with branches, bushes, or even simple boards like those used for construction, because they are not capable of receiving impurity. However, if the wood was at one time used as part of a chair, bed, or container, it is forbidden to roof a Succah with it. The Sages even forbade using the pieces of a broken container or bed for S'chach, despite the fact that they are no longer capable of receiving impurity, lest someone make the mistake of using them for S'chach while they are still whole. (Shulchan Arukh, Orekh Chaim 629:1,2).
The Sages also forbade building a Succah from foul-smelling materials, or roofing with S'chach from which leaves or worms fall, lest because of the foul smell or the falling leaves one leave the Succah and go into his house. Yet, if one already roofed with these sorts of branches one is not obligated to replace them. Still, if the stench in the Succah is so strong that people are unable to bear it, the Succah becomes invalidated in the eyes of the Torah, for it is not fitting for human habitation. (Ibid. 629,14; Mishna Berurah 38).2 - More Sun than Shade
The S'chach must act as a shield against the sun. Therefore, so long as it keeps out most of the sunlight it is Kosher, for we follow the majority. Yet, if even half of the sun's rays manage to penetrate the S'chach, the Succah is rendered invalid. This is gauged by looking at the S'chach itself as opposed to the floor of the Succah. This is because the sun's rays widen as they pass through the holes in the S'chach and descend to the earth, and it sometimes appears that there is more sunlight in the Succah than there is shade. All the same, if an examination of the S'chach itself shows that the shade is greater than the sunlight, the Succah is Kosher.
If under a small portion of the S'chach there is more sunlight than shade, the entire Succah as a whole remains Kosher. In such a situation, even those who sit under the weak S'chach where there is more sunlight than shade, fulfil the Mitzvah of dwelling in a Succah. One must make sure, though, that nowhere in the S'chach is there an area that occupies seven square handbreadths (56 cm x 56 cm [1' 10.05" x 1' 10.05"]) .in which the sunlight is greater than the shade. If this is the case then this area of the Succah is invalid.
Occasionally the S'chach is not arranged evenly, such that for part of the day there is more shade than sunlight, while during the rest of the day the amount of sunlight in the Succah exceeds that of the shade. In such a situation, Jewish law says that the Succah is judged according to the situation at noontime, when the sun is in the middle of the sky. If at that time the amount of shade in the Succah is greater than the amount of sun, it is Kosher; if not, it is not Kosher (Rema, 631:5).3 - Some Laws concerning S'chach
If in the Kosher S'chach there is an opening that possesses a width is three handbreadths (24 cm. [9.45"]), it is seen as causing a break in the S'chach and may quite possibly invalidate the Succah. This is because such an opening causes the Succah to be seen as not having three walls. If the opening's width is less than three handbreadths, yet contains enough room for the head or most of a person's body it does not disqualify the Succah, yet the one who sits under it has not fulfilled the obligation to dwell in the Succah. If the space is even smaller than this, it is as if nonexistent; therefore, one who sits under it fulfills the Mitzvah of dwelling in the Succah (Shulchan Arukh 632:2).
It is best to roof a Succah such that there be abundant shade inside. All the same, there should not be too much S'chach; there should not be so much S'chach that it becomes impossible to see the larger stars through it at nighttime. Yet even if one placed so much S'chach on the Succah that one cannot see the rays of the sun, the Succah remains Kosher (Ibid. 631:3). If, though, the amount of S'chach is so great that even the rain cannot penetrate it, Rabbenu Tam (Rabbi Yaakov ben Meir Tam) holds that such a Succah is not acceptable. This is because the Succah is meant to be a temporary dwelling, and if the rain cannot penetrate its roof, it is more like an actual house. One must abide by this ruling where possible (Mishna Berurah 631:6).4 - The Structure of a Kosher Succah
A Succah that is taller than twenty cubits (about 9.6 meters [31' 6"]) is not acceptable. This is because the Succah is meant to serve as a temporary dwelling, and a S'chach roof at such a height cannot be considered the roof of a temporary dwelling. If a Succah is shorter than ten handbreadths (80 cm. [2' 7.5"]), it is not Kosher. This is because it is not possible to sit in it, and a Succah must be suitable for sitting. Its width must be at least seven handbreadths (56 cm. [1' 10.05"]), for if it is any less than this even one person cannot sit inside of it with his meal.
The height of the Succah's walls must be at least ten handbreadths (80 cm. [2' 7.5"]). They must be built on the ground, and if there is a space of three handbreadths between the ground and the base of the wall, the wall is unacceptable, for it is so wide open that even goats can make their way under it. It is permissible, though, that there be space between the tops of the walls and the S'chach; if the walls themselves reach a height of ten handbreadths it is possible for the S'chach to be placed up to twenty cubits high, i.e., the maximum permissible height of a Succah. And even if a large space is left between the top of the wall and the S'chach it remains acceptable, for we view the wall as if it continues to rise up to the height of the S'chach (Shulchan Arukh 630:9).
The Succah must have two complete walls and a third whose length is at least one handbreadth. This law, though, gets somewhat more complex. From the words of the Torah, we learn that a Succah must have three walls, yet the Oral Tradition teaches that for the third wall one handbreadth is enough. This handbreadth has to be what the sages refer to as "a wide handbreadth," i.e., slightly more than a handbreadth. This third wall must stand at a distance of no more than three handbreadths from the Succah's second full wall. Any space that is less than three handbreadths is termed "Lavud," or attached. In this manner, the third wall becomes a wall of four complete handbreadths - the minimum necessary requirement for an acceptable Succah wall. The Sages also said that the remaining space of the wall must be made fit through what is known as "Tzurat HaPetach," or the form of an opening (Ibid. 639:2). The laws of such concepts as "Lavud," and "Tzurat HaPetuch" are many and detailed, so much so that Rabbi Moshe Isserles (Rema) writes that the accepted custom is to build three complete walls, for not everyone is versed in the laws of Succah walls (Ibid. 630:5). Ideally, one should build a quality Succah possessing four complete walls. The Succah should also have an doorway that can be closed in order that it be comfortable for living purposes, protecting the one who dwells in it from the wind, the sun, and animals.5 - A Succah under a House or a Tree
The Succah must be situated under the open sky, so that the S'chach, and not something else, be that which covers the one dwelling in the Succah. Therefore, a Succah made indoors, under a roof, is invalid. Similarly, it is forbidden to make a Succah under the branches of a tree.
It is permissible, though, to make a Succah next to the walls of a high building. Even if the walls of the building are very high and prevent the sunlight from reaching the Succah, it is Kosher. This is because only a roof or branches which are directly above the S'chach can render a Succah invalid; anything that is outside of the straight line running from the S'chach to the sky cannot invalidate the Succah.
If the branches that are above the S'chach are very sparse and the Succah's S'chach is so dense that even if the S'chach under the branches was removed, the remaining S'chach would be so thick that it provide more shade than sunlight, the Succah remains Kosher (Ibid. Orech Chaim 621:1).
It is also permissible to build one's Succah under clotheslines, for because their shade is very little, and their purpose is not to provide shade, they do not invalidate the S'chach below.6 - Sitting under the Shade of the Succah
Fulfilling the Mitzvah of the Succah means sitting in the shade of a Kosher Succah. Therefore, if one spreads sheets under the S'chach for additional shade he has in fact invalidated the Succah. It is permissible, though, for a person to sit in a Succah wearing a big hat on his head, because the hat is an appendage to his body and is not seen as causing a separation between he and the S'chach.
Similarly, it is permissible to hang different types of fruits and paper ornaments from the S'chach, for the ornaments are an appendage to the S'chach and are not viewed as a separation between the S'chach and those dwelling in the Succah. One must make sure, though, that the ornaments hang within a four handbreadths (32 cm. [1' 0.6"]) of the S'chach. Furthermore, even if the ornaments cover the entire S'chach, so long as they hang within four handbreadths of the S'chach, they are considered an appendage to the S'chach and do not render the Succah invalid. If one accidentally hung an ornament that dangles down below the four-handbreadth mark, so long as the width of the ornament is less than four handbreadths, it does not invalidate the Succah. One must be careful, though, not to sit under it. If the width of the ornament is less than three handbreadths (24 cm. [9.45"]), though it is permissible to sit under it, it is preferable not to. Rather, one should take care to raise all such ornaments to within four handbreadths of the S'chach.
One who sleeps in a bed to which a canopy has been permanently attached does not fulfill the Mitzvah of Succah. If the canopy, though, is of a temporary nature, its status depends upon its height: If the canopy is lower than ten handbreadths, it lacks significance and is considered an appendage to the Succah. One who sleeps in such a bed therefore fulfills the Mitzvah of Succah. If, though, its height is greater than ten handbreadths, the canopy possesses significance and one who sleeps under it does not fulfill the Mitzvah of Succah.
The space under a bed or a table inside the Succah, because it is created unintentionally, is considered temporary. Its status therefore depends on its height. If the space underneath the table or bed is of a height less than ten handbreadths (80 cm. [2' 7.5"]) one that sleeps under it fulfills the Mitzvah of Succah. If, though, the space is greater than ten handbreadths in height, one who sleeps there does not fulfill the Mitzvah of Succah.
The same rule holds true when it comes to a bunk bed. If the space between the two beds is more than ten handbreadths, the one who sleeps in the bottom bed does not fulfill the Mitzvah of Succah. If the space, though, is less than ten handbreadths, one who sleeps in the bottom bed fulfills the Mitzvah (see Piskei Teshuva, 627:3).
If a protective covering is placed on the Succah it is clearly rendered invalid, for the covering acts as a partition between the S'chach and the sky. Yet, after the covering has been removed, the Succah again becomes acceptable. One must be careful, though, that when building the Succah this covering be rolled up to the side in such a manner that it not constitute a partition between the S'chach and the sky. This is because there are Torah authorities who hold that if at the time of the construction of the Succah the S'chach is overlaid with a covering, even after removing the covering the Succah remains invalid. The reason for this is that the act of making a Succah acceptable must be through placing the S'chach upon it and not through removing a covering from it (Bach, Mishna Berurah 626:18; but Rema is lenient, 626:3).