Dear Dairy Excerpted and adapted from a shiur by Rav Yosef Jacobovits May 13, 2021…
Dayan Yehoshua Grunwald
February 18, 2021
Q My window shades fell down on Shabbos. Would I have been permitted to rehang them?
A One of the 39 melachos of Shabbos is boneh (building). In addition to new construction, the melacha includes repairing or adding to an existing structure.
We will focus here on additions to structures that are either a) connected to the ground, or b) not connected to the ground, but at least 40 se’ah in volume (about 11.5 cubit feet, according to some views).
Such additions can be divided into three categories:
- If the addition is permanent and enhances the structure either functionally or cosmetically, it is prohibited Biblically. Example: placing a shelf on pegs in a closet that is either attached to the ground or 40 se’ah in size.
- If the addition is intended to be permanent, but a) it is connected loosely, and one doesn’t mind that it wiggles at the place of connection, b) it can be connected with minimal energy and skill, and c) it has an independent function rather than just enhancing the structure it’s attached to, it is permitted according to most poskim(Mishnah Berurah 315:7, but see Chazon Ish 52:13).
- An addition that is meant to be detached and reattached regularly, if it is a) recognizable as such, and b) not connected tightly, it may be attached and detached on Shabbos. (If one of these conditions is missing, it is Rabbinically forbidden.) Examples include a fridge magnet and a child-safety gate that fits into a track.
Because window shades are generally kept hanging until they are discarded, and they have the same function—protection from the elements—as the house, rather than an independent function, rehanging them would belong in the first category and be Biblically forbidden.