A manufacturer in Eretz Yisrael developed waterproof Sechach, which has gutters on either side such that if the Sechach is properly arranged, rain will not enter the Sukka. At first glance, there should be no problem whatsoever using such Sechach. After all, it is constructed from wood, and it does not constitute a Halachic "Keli" (utensil). It is only because of its unique style that it keeps the rain out of the Sukka, but all the qualifications of Sechach seem to be met. Seemingly, then, this Sechach would not only be permissible, but even recommended, especially in places such as Panama and the United States where rain is very common during Sukkot. Such Sechach enables one to continue performing the Misva of Sukka even under rainy conditions, and it thus might seem preferable to use such Sechach.
Indeed, Rav Yosef Shalom Elyashiv (1910-2012), in Sefer Ha’sukka, ruled that it is permissible and even recommended to use this rainproof Sukka. He was then asked how to reconcile his ruling with the custom recorded by the Tur (Rabbenu Yaakob Ben Asher, 1269-1343), in the name of the Samak (Sefer Misvot Katan by Rabbi Yishak of Corbeil, 13th century), not to construct Sukkot with impenetrable Sechach. According to this custom, which is codified by the Shulhan Aruch, the Sechach must be a temporary covering which does not protect the Sukka from the elements. Rav Elyashiv responded that this refers to very dense Sechach which cannot be penetrated by wind, rain or insects, and such Sechach cannot be used because the Sukka must be a crude, temporary structure. The new rainproof Sechach, by contrast, has spaces through which wind and insects can enter the Sukka, but is constructed in such a way that rain immediately falls off the Sechach without entering the Sukka. Such Sechach does not violate the requirement to use a temporary covering. This is also the position taken by Rav Elyashiv’s son-in-law, Rav Haim Kanievsky (contemporary), in Sheraga Meir.
Several other Poskim, however, disagreed. The Shebet Ha’levi (Rav Shemuel Wosner, contemporary) wrote that we should not be trying to "outsmart" Halacha by devising creative strategies, and we should use the same kind of Sechach that Jews have been using for generations. Likewise, the Kinyan Ha’Torah maintained that although rainproof Sechach might be technically permissible, one should use the traditional Sechach. This is also the view of Rabbi Yishak Yaakob Weiss of the Eda Ha’haredit (in Keneh Ha’bosem). The Yalkut Yosef (Sukka, p. 85) cites both views without reaching a conclusion, and it appears that Hacham Ovadia Yosef did not issue a ruling on this issue.
In light of the difference of opinion that exists, it would seem that one should preferably not use such Sechach, especially given the fact that we are dealing with a Biblical obligation. However, one who already owns this Sechach may certainly rely on the ruling of Rav Elyashiv and use it for the Misva.
On a more general note, this discussion should remind us that the Shechach must be a crude, temporary covering of the Sukka, and not a strong, permanent roof.
Summary: The leading Halachic authorities debate the question of whether one may use the recently-developed Sechach with gutters that does not allow rain into the Sukka. It is best not to use such Sechach, but one who does has Halachic authorities on whom to rely.
