Halachot Of The Schach And Walls , The Schach Mat
It is the minhag today to use schach made out of mat reeds (this could be either bamboo or slats) which are attached together by strings. Using such a mat has certain problems:halachik
Problem #1: Under certain conditions this mat may be considered to be a utensil, and as such a utensil is pussel as schach since a utensil could receive tumah.
The Mishnah states that a large mat which is made for lying down on is susceptible to tumah and may not be used as schach. However if an identical mat was created for the purpose of schach then the mat is not susceptible to tumah and would be permitted to be used as schach.
However the Mishnah Brurah was strict about this and states: “You should know that in these places all mats are used for (the purpose) of lying down on. If so even if the mat was created for the purpose of schach – you still may not use it as schach.” (In other words, The Mishnah Brurah held that the intent of what the mat was made for is irrelevant, and is always forbidden to be used since the world at .large uses it for the purpose of a mattress to lie down on)
Problem #2: The mat has the appearance of having a regular ceiling (Gezairat Tikra). When all the slats are attached to one another, this mat (according to the Rashba) would be considered one unit, and a ceiling – and it is pussel..
Problem #3: Because of gezairat ma’amid – which is that the Chachamim prohibited tying the schach to the beams underneath it or tying the schach to the succah itself, using anything that can receive tumah (such as ropes). Overall they prohibited tying the schach down with anything that is not gedulei karkah (natural materials that grow from the earth); as such even strings of metal would be prohibited as they are not gedulei karkah.
The reason for this gezaira was that one should not come to use the tying materials (i.e. the rope or metal) as schach itself. Therefore a problem arises with the strings which one uses to tie the mat itself.
So Why Can We Use Mats?: Despite the problems listed above, many of today’s poskim permit the use of a mat, since nowadays a mat is rarely used for the purpose of sleeping and therefore it does not attain the identity (or status) of a utensil and as such is not susceptible to impurity.
Also the poskim state that the mat can not be compared to a ceiling since the mat is soft and folds up (it is flexible) and as such it is also not comparable to slats (This was the psak of both Rav Shlomo Zalman Aurebach zt’l and Rav Vosner .shlita.)
Regarding the problem of gezairat ma’amid (Problem #3 above): the mats that have a mehadrin Hechsher are strict to only use fiber or strings from materials that grew from the land and that did not go through any processing or restructuring. This way the strings do not receive tumah and using them is kosher.
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