why is it that we say that acc to R' Zeira among others that if the Suka is higher than 20 it is posul because the shade is from the walls. the question is where do we measure this by. At 12 o' clock the shade will be produced by the S'chach. and furthermore even if a Sucka is under 20 amos for a very large part of the day the shade will be provided by the walls. so the question is what exactly is the geder here. your comments will be greatly appreciated and even more so if they are backed up mairai mokomos. Thanks in advance
Binyomin Samson, England
We had a wonderful lecture on the subject by Rav Alexander Schutz in the beginning of Sukah. (The link to our video archive of the Shiur is: www.dafyomi.co.il/lectures/marei-suka008.htm .) The gist of it was that even at noon of the summer solstice, the sun is not directly overhead unless you live in the tropics. The Gemara's calculation works perfectly for the highest latitude in Israel.
This doesn't do the Shiur justice, of course. See it for yourself and enjoy!
The "Antwerp Sukah":
It seems that one cannot discuss the topic of waterproof Sukot without mentioning the controversy in the 1980s when someone in Antwerp invented a Sukah, designed with two layers of Sechach and with drains, in such a way that the Sechach was not thick but rain could still not enter the Sukah.
1) Most authorities permitted this Sukah. Rav Yosef Shalom Elyashiv zt'l, in his Collected Responsa vol. 1, chapter 61 (top of page 90), wrote that it is obvious and clear that the entire Pesul according to Tosfos is because since rain cannot enter, this means that the Sukah has become a permanent dwelling place, since it is covered over entirely. It is similar to a Sukah that is covered with Sechach which is so thick that the Sukah is like a house.
According to this, the Antwerp Sukah is Kosher because the Sechach covering is not thick, even though it has been designed in such a way that the rain cannot get in.
According to Rav Elyashiv a Sukah can certainly be waterproof without being Kavu'a.
2) Rav Shlomo Zalman Auerbach zt'l (in Halichos Shlomo, Tishrei-Adar, page 129) also said that if planks which are Kosher as Sechach are used in a way that they prevent rain from entering, but the Sechach is temporary and one can see the stars through it, this is Kosher l'Chatchilah.
(It seems to me that according to this, Kavu'a Sechach cannot be defined as that which does not let any water in because even non-Kavu'a Sechach is capable of not letting any water in.)
3) However, Rav Meir Bransdorfer zt'l (Teshuvos Keneh Bosem 2:27) disqualified the Antwerp Sukah, and Dayan Weiss (the author of Minchas Yitzchak) agreed with him. They argued that since average rain cannot enter, one should not allow the Sukah. Acording to their view, a Sukah cannot be waterproof without being Kavu'a.
4) Summary and conclusion:
At this stage I think we should consolidate the opinions that I have cited above and try to reach some clarity. I must say that this question looked like a very simple one when we started, but we have seen that it is in fact the subject of a lot of discussion among the earlier and later Mefarshim.
a) I have cited a number of opinions and now we should explore whether these different opinions agree with each other or there is a dispute. First, I should point out that the Magen Avraham that I cited in the first reply cannot be consistent with Rav Shlomo Kluger that I cited. The Magen Avraham writes that if the Sechach is fixed in with nails, this automatically disqualifies the Sukah even if the rain can still get in, while Rav Kluger writes that the Sukah is only Pasul if the rain also cannot enter.
b) I also point out that it is worth considering what the Maharam, that I cited in my first reply, would have said about the "Antwerp Sukah" (which, of course, was designed hundreds of years after his lifetime). I cite again the words of the Maharam:
"One should not cover the Sukah permanently with planks in such a way that the rain will not enter."
We would think that the simple reading of this is that the crucial point is whether the rain can enter, and if it cannot enter this proves that the Sukah has been made as too permanent a structure to be valid, and so the Antwerp Sukah would not be acceptable. However, some might argue that according to the Maharam the crucial point is that the Sukah should not be permanent, while the rain is only a secondary factor. I will leave this point open.
c) Finally, I will conclude with one of the chief sources of the opinion of Rabeinu Tam.
(Even though Tosfos, end of 2a, does not actually mention Rabeinu Tam, it is nevertheless well-known that the champion of the opinion that rain must be able to enter the Sukah is in fact Rabeinu Tam.)
The Hagahos Maimoniyos (Hilchos Sukah, ch. 5, #9 (printed on the same page as the Rambam)) writes that once Rabeinu Shimshon, the brother-in-law of Rabeinu Tam, made the Sechach out of planks less than four Tefachim wide and built a very nice Sukah like an Arch, fixed in with nails. Rabeinu Tam said the Sukah was invalid because it prevented the rain from entering.
Again, I suggest that the above implies that the crucial problem with the Sukah was the fact that the rain could not enter. This was why Rabeinu Tam said it was Pasul. The fact that it was made in a beautiful, permanent way was not sufficient reason to disqualify the Sukah.