Ed. Before leaving this siman, I would like to attempt (be”H) a brief summary lesson to clarify and simplify some of the major points of ‘boneh’ and ‘ohel’. We will not include all definitions (e.g. what is permanent vs. what is temporary); rather, we will merely identify the major categories of the halacha, and the basic ruling for each. In addition, we will quote some common examples taken from The 39 Melachos by Rabbi Ribiat.
‘Boneh’ (building) according to the Torah includes any permanent-like structure, whether it be just a roof or just walls. Even adding to such a structure on Shabbos is forbidden from the Torah. Thus the term ‘ohel kavua’ (a permanent ‘tent’), then, is associated with a Torah prohibition.
Example (p. 1010): A Sukkah is considered to be a full-fledged permanent shelter since it is designed to last for more than 7 days. Erecting, or merely securing a Sukkah is therefore… the melacha d’Oraisa (from the Torah) of Boneh.
‘Ohel arai’ (a temporary ‘tent’) is a Rabbinic prohibition. In this summary, this term describes a structure that has a temporary roof (with or without walls), but not one that has only walls. (Note: The latter will be called a ‘mechitza’ – see below.) If an ‘ohel arai’ is a roof with no more than two walls, creating the ‘ohel’ is prohibited only if the space under it is needed for use. If there are 3 or 4 walls, creating the ‘ohel’ is prohibited even if the space under it is not needed for use. In all cases, it is permitted to add to an existing ‘ohel arai’.
Example (p. 1083): One may not drape a canopy or screen-like netting over a play-pen or over a bed or crib frame for privacy or to protect from insects… However, if the screening material was attached at one end (e.g. tied to the frame or posts) prior to Shabbos, and has cords for drawing it over the bed or crib, spreading the covering or screening would be permitted.
‘Mechitza hamateres’ refers to a temporary wall (only, i.e. no roof) that serves a halachic purpose. It is prohibited to be put up.
Example (p. 1087): A partition may not be set up as a halachic divider in a bedroom (i.e. where a couple resides) in which there is a Sefer Torah. Since the sanctity of the Sefer Torah requires a halachic separation from the privacy of the bedroom, this halachically-defined partition is considered substantial and is therefore similar to Boneh. (Note: A mechitza separating between men and women in a shul is NOT a ‘mechitza hamateres’, for reasons that cannot be explained at this time!)
‘Mechitza’ refers here to a temporary wall that serves no halachic purpose. There is no prohibition against putting such a wall up.
Example (p. 1085): Children’s safety gates installed at the top of stairs may be opened and closed with no restrictions at all… even if they are designed to expand and remain firmly wedged and held in place between the walls (i.e. not attached to the wall on hinges.) There reason they are permitted is because they are designed to be regularly set up and taken down (i.e. they are ‘arai’ - temporary).
One final point (excerpted from an earlier lesson): What would mitigate either an ‘ohel’ or a ‘boneh’ prohibition is when a ‘keli’ (utensil) is already assembled, but it is folded up. As these ‘keilim’ are already fully assembled and built, opening or unfolding them does not constitute building or erecting a new structure.
Examples (p. 1051): a folding bed or cot, a folding chair or bench, a folding table, a folding playpen, a folding crib (e.g. porta-crib), a folding “umbrella” stroller, a “futon” (couch that folds down into a bed)