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11. The Biblical Prohibition to make a hole in a wall, floor, or vessel which holds 40 Seah:
A. The general rule:
A wall or floor: One who hammers a peg into the wall in order to hang vessels and the like on it, is liable for [the] building [prohibition]. [Furthermore] even if one did not [yet] hammer the peg [into the wall] but drilled a hole in the wall in which the peg will be inserted into, he is liable for [the] building [prohibition] on this hole [that he drilled] since this hole is an accessory for the building, which is the inserting the peg. Similarly one who makes a hole in the floor of his house to drain out the water is liable for [the] building [prohibition].
Making a hole in a vessel which holds 40 Seah: A large barrel or other large vessels which hold 40 seah carry with them the building and destroying [prohibition], and has the same law as ….a wall.
Regarding making holes in vessels which do not hold 40 Seah –See above Chapter 1 Halacha 6C for the full details of this subject.
B. Removing a knife from a wall:
The custom in a case that a hole will inevitably be widened in a wall, such as when removing a knife jammed in a wooden wall: [Although the Sages allowed one to remove a knife that was inserted into a vessel detached from the ground, as explained above in Chapter 1 Halacha 6C] nevertheless a knife which was inserted into a wooden wall before Shabbos, if it has been somewhat firmly inserted, the custom is to forbid removing it on Shabbos unless one had removed it already one time before Shabbos, as in such a case it is no longer inevitable to avoid widening the hole. However, when one has never yet removed the knife from this hole it is impossible to avoid widening the hole upon removing it on Shabbos, being that it was somewhat firmly inserted into the wall.
The reason for the above custom: [Now, although this hole is widened unintentionally, nevertheless the Sages] only permitted to widen [a hole] unintentionally by a barrel, being that even to initially make a hole intentionally [in a barrel] only involves a Rabbinical prohibition. However, [since] one who makes a hole in a wall with intention is at times liable for a Chatas Offering, such as if he punctured it in order to insert a peg into [the wall], and even one who widens this hole the tiniest amount with intention is [also] liable, therefore it should receive the stringency not to add to [the hole] even if he has no intention in doing so, if it is inevitable to avoid.
The reason that from the letter of the law the above is allowed: This is the reason behind the [above] custom. However, from the letter of the law this is not a clear prohibition being that even if one were to initially make a new hole in the wall in the exact same scenario as above when one widens the hole through removing the knife, which is done not for the sake of inserting a peg into, then doing so would not involve a Biblical prohibition being that [a)] it is an action which is not done for its use, as well as [b)] that he is damaging the wall, as well as [c)] that the widening of the hole made through removing the knife is an irregular way of making [a hole], and all [actions done] irregularly do not at all carry any Biblical prohibition even by a complete [form of forbidden] action [and certainly here that the action itself is not a complete prohibition due to reason a) and b)]. Therefore, it should not be prohibited to widen [the hole] unintentionally just like it was not prohibited by a barrel in accordance to what was explained there that the main opinion is like those that permit doing so.
Must one be stringent like the custom: Nevertheless one may not be lenient against [following] this custom.
Making a hole in the wall of a building [or vessel that holds 40 seah or is attached to the ground]: Is prohibited due to that it is considered building. If one does so with intention to insert a nail and the like into the wall then this is Biblically prohibited. If, however, it is not done with intent to stick anything in it, then it is only Rabbinically prohibited.
May one remove a knife from a wall on Shabbos? If the knife had been removed once before Shabbos and then reinserted, it may be removed on Shabbos. If it has never been removed before then the custom is to not allow to remove it on Shabbos because it inevitably widens the hole
May one widen an already existing hole? It carries the same laws as one who initially makes the hole on Shabbos both by walls and vessels.
May one enter a nail or other item into an already existing hole?
Any item which is commonly firmly attached to a wall, such as a nail or hook, may not be placed even loosely into a pre-existing hole on Shabbos, even if the hole is wider than the item. However, an item which is not meant to be firmly attached to the wall, such as a key and the like, may be inserted even semi-firmly into a hole in the wall, as long as he does not widen the hole in the process.
May one attach a wall hanger or hook to his wall or door on Shabbos?
This is forbidden, whether attaching it using glue, tape, or a suction item, due to the building prohibition.
Question: [Thursday, 16th Sivan 5781]
Dear Rabbi, we have a makeshift curtain that we constructed over our sliding door to shade from the sun in the afternoons and for privacy purposes and the way it works is that one side is nailed into the wall on one end of the sliding door and the other side has a nail that is punctured through the curtain and there is a hole that is made on the other side of the sliding door into which this nail with the curtain can be entered into. This nail that is attached to the curtain is meant for constant removal and insertion into the hole in the wall, as we see fit. My question is whether this may be done on Shabbos or is it considered like building being that I am inserting a nail into the wall?
You should not do so on Shabbos due to worry that you may come to make a bigger hole in the wall in the process in order so it remain firmly inside, as well as due to a rabbinical decree that the onlooker does not know your intent of removing it and hence it appears like building. Rather, simply nail in a permanent nail to that side of the wall and make a hole in the curtain which you can then hang onto the nail and remove. In all cases, when you place the curtain onto the nail you have to be careful that it does not hover a Tefach over the ground due to the Ohel prohibition, and thus you should first stretch it out fully [without any forward bends in the curtain] and only then hang it.
Explanation: Generally, inserting a nail into a wall on Shabbos consists of the biblical building prohibition [i.e. Boneh] while removing it consists of the destroying prohibition [i.e. Soser]. This applies even if the nail was only loosely attached to the wall. Nonetheless, this only applies if the nail is meant to last at least temporarily, while if it is meant for constant removal and insertion then it’s insertion and removal does not contain a building prohibition, and it is for this reason that the Poskim rule that a knife may be inserted and removed from a wall on Shabbos. Nonetheless, this only applies if the corresponding hole in the wall was made before Shabbos and the knife was inserted into it at least one time and then removed, otherwise we suspect that the removal can cause the hole to widen which would transgress the building prohibition. Now, seemingly we can apply the same rules regarding the above type of curtain nail, that if it was nailed in and removed once before Shabbos, then it is permitted to enter and remove on Shabbos as well so long as it does not make any more of a hole, being that it is meant for constant removal and insertion. However, in truth the cases are not the same, as everyone understands that a knife in a wall is meant for constant removal and insertion, in contrast to a nail which is commonly left inside a wall for permanent basis. Hence, while one can argue that there is no Biblical prohibition involved in doing the above on Shabbos, nonetheless there is room to learn that it would be rabbinically prohibited due to the fact that it appears like one is building. We find a similar concept brought in the Talmud and Poskim regarding pegs and bolts of a door that it does not suffice for them simply to be meant for constant opening and closing, which they are, but rather they must also contain a clear recognition that they are not meant to be nullified there, and hence seemingly the same would apply here. This applies even though the nail will only be loosely fit into the hole as nonetheless to the onlooker it may appear like building. Another possible concern with a nail is that one will push it in too deep and end up making a larger hole. [Another possible issue to raise in the above case is the fact that we find regarding other Halachas worry that one may come to leave the item there forever, and so too here perhaps one will choose to leave that side of the curtain there forever and rather open the other side. However, in truth this is not a worry at all, as whenever one side is already permanently fixed, we do not assume that one will come to change his mind regarding the other side.] Therefore, my conclusion is as above, that the above should not be done due to a possible rabbinical prohibition, and rather one should hammer a permanent nail into that side of the sliding door and make a hole in the curtain before Shabbos which he can then hang onto the permanent nail and remove it as he sees fit, as hanging a curtain on a nail does not contain any prohibition on Shabbos if one make sure that it does not hover a Tefach over the ground, which is beyond the scope of this explanation to elaborate on..
Sources: See regarding the Biblical prohibition against nailing a nail into the wall: Admur 314:2; See regarding the prohibition of removing an item from the hole for the first time and thereby widening the hole and the allowance to enter and remove a knife from a hole in the wall: Admur 314:4; Michaber 314:12; M”A 314:5; Taz 314:2; M”B 314:11; Regarding the law of pegs and bolts see: Admur 313:3; Regarding rabbinical decree against placing a nail into a hole even very loosely due to worry that one may come to put it in strongly, see: Ketzos Hashulchan 119 footnote 4; Regarding the worry that one may come to nullify one of the sides there, see: Admur 317:10; Regarding being careful that the curtain does not hover a Tefach over the floor, see: Admur 315:7; Rama 315:1; Michaber 315:12; Rambam 22:32
 Admur 314:2
 Admur 314:2
 Admur 314:5; as well as 313:18, brought above in Chapter 2 Halacha 2B
 which falls under the Makeh Bepatish prohibition as opposed to the building prohibition
 Admur 314:4; Michaber 314:12; M”A 314:5; Taz 314:2; M”B 314:11
 Admur ibid; M”A ibid; Taz ibid; M”B ibid
 Admur 314:2
 Admur 314:4
 Halacha 4
 Halacha 2 and 3
 Ketzos Hashulchan 119 footnote 4 Vetzaruch Iyun from chapter 313 Halacha 21 that one should not reassemble cups even if never done in a firm way.
 This is forbidden due to suspicion that one may come to insert the nail firmly or even semi-firmly into the hole and be liable for building.
 Az Nidbaru 3:23