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4. Dismantling a roofing on Shabbos:
The rule: Any tent which is allowed to be mantled and [thus] does not involve [the] building [prohibition], then it likewise does not involve [the] destroying [prohibition] and is [thus] permitted to be dismantled.
Removing a sheet from a bed barred with ropes: If this bed does not have placed on it leather or boards but is rather barred with ropes from above, then if there are three handbreadths between each rope, in which case we do not consider the ropes to be all attached, then it is forbidden to initially spread a sheet over it on Shabbos or place a pillow or blanket on it being that this is similar to making a tent. Similarly, it is forbidden to remove the lower cloth that is on it being that this is similar to destroying a tent. [Thus, one may never undo a hovering if it is hovering over a Tefach of space and has walls under it, even it was not made for protection purposes, if the space under is used.]
Removing the cloth covering from the barrel: The same law applies [regarding removing the cloth from the barrel] that it is forbidden to remove [a cloth] covering which covers its entire mouth if it lacks a handbreadth worth of liquid, because it is similar to destroying a tent.
Dismantling the added material to a temporary tent: When one adds onto a tent that was [the width of] a handbreadth from before Shabbos, it is only permitted to dismantle the material that was added [on Shabbos] however not the part of the tent that was [already] built from before Shabbos.
Whenever it is forbidden to initially set up a roofing on Shabbos then it is likewise forbidden to take it down. Thus when adding to the handbreadth of a roofing on Shabbos one may only dismantle the added material and not any of the handbreadth material which was set up from before Shabbos.
May one dismantle a roofing which was spread from before Shabbos up to a handbreadth of the roofing?
A permanent roofing: Is forbidden according to all.
From the Rav’s Desk
I own a swing set with a canopy like hovering on top to block the sun. The canopy can be moved in different positions, such as horizontal/flat to completely shade from the sun, or upright/vertical, to only block the sun partially. My question is whether I may move it up and down on Shabbos.
It is forbidden to create or undo a hovering which was made for protection purposes on Shabbos. Hence, clearly one may not take off the hovering to stop it from blocking the sun, and may not erect it initially on Shabbos so it block the sun. However, here that it is already erected, then there is possibility for allowance, in the following case: If even in its vertical state it still hovers one Tefach [8 centimeters in width] over the swing, then if it was standing in this state before Shabbos it may be further opened to its flat state on Shabbos without issue, and then further closed to its vertical state if desired. However, if it was opened before Shabbos to its full flat state, then seemingly one may not tilt it upwards which will cause some of its flatness to no longer be an Ohel-hovering. If, however, it will always remain a hovering and no part of the materiel will become actually vertical [but just a slanted hovering versus a flat hovering], then seemingly it may be opened and closed without issue, as there is no issue with changing the positions and moving an already established hovering on Shabbos. Practically, I suggest that before Shabbos you open the hovering to its full vertical state, with a single Tefach of stretched hovering, so you can then be allowed on Shabbos to open and close it as needed.
Sources: See Admur 315:1-2; 16 [may not dismantle the part which hovered before Shabbos]; Michaber 315:1-2; Shabbos 125b; Avnei Nezer 211:34 brought in Ketzos Hashulchan 120 footnote 17 [permits dismantling up until Tefach]; Chazon Ish 52:7
 Admur 315:16; M”A 315:14; M”B 315:38
 Admur 315:10; Michaber 315:4
 See Shaar Hatziyon 315:31 that from here we see that the prohibition of Setira is more severe than the Issur of Noeh, as one may build this type of bed if the walls were already around before Shabbos [if it is not the size of a barrel] but may not take it apart.
 Admur 315:19; Taz 315:11
 Admur 315:16
Other opinions: Some Poskim rule that the entire roofing may be dismantled. [Chazon Ish 52:7; SSH”K 24 footnote 31 allows this to be done in stages]
 Admur 315:10
 Admur 315:16
 Avnei Nezer 211:34 brought in Ketzos Hashulchan 120 footnote 17. So seems to also be the opinion of the Ketzos Hashulchan himself, [see Piskeiy Teshuvos 315 which plainly brings the Ketzos Hashulchan as following this ruling] although he brings that from the Lashon of Admur “it is only permitted to dismantle the material that was added on Shabbos” it seems that it is forbidden.
 The reason: As just like it is permitted to add if there is one Tefach material so too one can take away up until one Tefach of material.
 Chazon Ish 52:7
 See footnote above in lenient opinion.