Introduction
1. When the Beis Hamikdash was destroyed, many Jews wanted to decree actual aveilus on themselves by not eating meat or drinking wine, as those were brought on the Mizbeiach. R’ Yehoshua responded (גמ' ב''ב דף ס' ע''ב), ”A gezeira may not be made for the tzibbur unless the majority of the tzibbur can handle it.” Thus, instead of absolute aveilus, Chazal instituted limited, yet constant, takanos, particularly regarding matters of joy. These serve as a memory of the Churban literally in our daily life, in fulfillment of the posuk "אם לא אעלה את ירושלים על ראש שמחתי." These pertain to the house, meals, women’s jewelry, and a chosson’s joy.
2. These takanos are fixed in halacha and apply at all times, in all places, to this day, as is clear from Shulchan Aruch (או''ח סי' תק''ס). Since Chazal instituted these decrees, obviously the majority of the tzibbur can in fact handle them. Thus, we must be meticulous about them. Even if we only bear the sin of not mourning Yerushalayim properly, that is enough to extend our galus (סידור ר' יעקב עמדין, שער שלכת שער הדלק חלון ו' אות ט''ז).
One Square Amah in the House
Zecher l’Churban
3. After the Beis Hamikdash was destroyed, the Chachamim of that generation decreed that when one builds a house, plasters it, and whitewashes it with lime, he must leave over a one-square-amah area on the house without lime to remember the Churban (שו''ע סי' תק''ס ס''א). In other words, there is a chiyuv to leave an area on the wall that does not have the desired finish so that it is noticeably lacking and flawed. This causes us to constantly remember we are missing something much bigger: the great, awe-inspiring Beis Hamikdash.
Applies Everywhere
4. Chutz l’Aretz. Everyone agrees this halacha applies everywhere in Chutz l’Aretz; there is not a single opinion that holds it does not.
5. Yerushalayim. Some cite a minhag not to require making reminders of the Churban in the Old City of Yerushalayim, since the residents constantly see the Churban with their own eyes (הגרע''י שלעזינגער בעל לב העברי, ס' הבית מילואים עמ' תפ''ד בשם הגר''מ הלברשטאם).
6. However, most poskim hold there is no such distinction, and even in the Old City of Yerushalayim one must leave over an amah of Churban to remember the house (ס' א''י סי' כ''ג ס''ד).
7. Eretz Yisroel. Some hold this halacha only applies in Chutz l’Aretz, as it demonstrates we do not have true acquisitions in Chutz l’Aretz. We only live there temporarily; we do not plan to reside permanently there (מהרש''א ב''ב דף ס' ע''ב, ס' הבית סי' י''ט הע' א' בשם מדרש תלפיות ערך בנין).
8. However, most poskim do not differentiate. They hold it also applies in Eretz Yisroel (שו''ת אז נדברו ח''ז סי' ע''ג).
Minhag in the Past
9. Many houses do not have an unfinished square amah to remember the Churban. The question is: what is the basis for this? Multiple Acharonim attested that the contemporary minhag was not to leave an unfinished space (שערי תשובה, מ''ב שם סק''ב), but many Acharonim wondered about the basis for this heter, which has gotten to the point that this halacha is virtually forgotten by Klal Yisroel without a valid reason (שערי תשובה סק''א, קיצור שו''ע סי' קכ''ו ס''א, נשמת אדם כלל קל''ז סק''א, מ''ב שם). We find multiple angles of heter in the Acharonim, and we must discuss whether there truly is basis to rely on, as will be explained.
10. Limestone mixed with sand. Some are meikel to say the whole chiyuv to leave unfinished space is only when whitewashing with lime. If, however, sand is mixed with lime, it is not called “lime,” which carries a chiyuv to leave unfinished space. Thus, there is no need to leave anything unfinished. Some explain this is what earlier generations relied on not to leave unfinished space since they mixed sand with lime (נשמת אדם, מ''ב שם).
11. However, some wonder about this rationale, as people today use just lime without sand—again, what do they rely on not to leave anything unfinished? (מ''ב שם)
12. Very white lime. Some propose another possible reason people are meikel: the issur is only with a very white type of lime. The lime that people used, though, was not so white, so perhaps there is no chiyuv to leave unfinished space (ב''מ שם). However, this is also dismissed, as it does not make sense they only made the issur on very white lime (מ''ב שם).
13. Non-Jews are particular. Some cite as a reason for the common practice of heter that we live among non-Jews, and they insist houses must be completely whitewashed (דעת תורה, אורחות חיים סק''ד). Obviously, this reason does not apply today whatsoever. Even if they are particular about the appearance of houses, that is only for the exterior. For the interior, each person can do what he wants. Thus, this is not a valid reason whatsoever for heter today.
14. Liquid whitewash. Some suggest the reason people are meikel is because Chazal only instituted a chiyuv to leave unfinished space when applying solid lime. They did not make a chiyuv to leave unfinished space when applying liquid whitewash, which has been in use since recent times, as it merely looks like lime but is not actually lime (שו''ת התעוררות תשובה ח''א סי' קס''ד).
15. However, the Acharonim do not agree with this either, as we do not find Chazal made such a distinction.
In Practice
16. Since this is a clear halacha paskened in Shulchan Aruch, and the fact that many people do not do it surprised and pained the leading poskim (above, 9); and we have seen there is no room for the reasons used to be meikel (10-15); this important halacha should be restored to its original status and followed properly. Many earlier gedolim did this (הגה''ק מוטשאטש, הגה''ק מבעלזא הובא בשו''ת משכנות הרועים סי' ח''י, הגה''ק חת''ס מנהגי חת''ס החדש פי''ג סכ''א, הגה''ק מצאנז אחרי שעודד אותו הגר''ה מקאלאמייע לזה, הגה''ק מסאטמאר, החזו'''א והקהילות יעקב ועוד).
17. Mark for the Beis Hamikdash in our houses. Thus, everyone should be careful about this going forward. Even if we did not do so before today, from today and on the matter should be rectified, both in Eretz Yisroel (8) and Chutz l’Aretz (4), and certainly in the summer homes people have in various places.
18. Let us think for a moment. For every small fix or minor flaw in our houses, we rush to bring in professionals and pay money so that our houses are beautiful and fixed up. If so, it is that much more incumbent upon us to invest in fixing up our houses to found them on meticulousness in halacha, even if it costs a bit of money.
19. How are we able to live in our comfortable houses, which stretch over hundreds and even thousands of square amos of beauty and spaciousness, without leaving a small unfinished space of one square amah without plaster in memory of the Churban? The Beis Hamikdash and the Shechina’s honor are worth us feeling pain over them, as we should. Let us express in our private homes the yearning for the rebuilding of Hashem’s House, במהרה בימינו.
