Mishnah Oholot 13

¹One who makes a new light hole, its minimum size is that of a hole made by the large drill of the Temple chamber. The remains of a light-hole [the size is] two fingerbreadths high by a thumb-breadth broad. The following is considered the remains of a light-hole: a window that a person had blocked up but had not been able to finish [being blocked up]. [A hole] that was bored by water, or by reptiles or eaten away by salt: the minimum size is that of a fist. If he intended to use it, its minimum size is one handbreadth square; For lighting its minimum size is that of a hole made by the drill. The holes in grating or lattice-work may be joined together to form [an opening] the size of a hole made by the drill, according to the opinion of Bet Shammai. Bet Hillel says: unless there is a hole of the size made by the drill in one place. [The above applies] for purposes of allowing the uncleanness to come in or to go out. Rabbi Shimon says: only for allowing the uncleanness to come in; but for allowing the uncleanness to go out [the minimum size] is one handbreadth square. ²[With regard to] a window made for letting in air, its minimum size is that of a hole made by the drill. If a house was built outside it, its minimum size becomes one handbreadth square. If a roof was placed at the height of the middle of the window, the minimum size of the lower part is one handbreadth square and of the upper part that of a hole made by the drill. ³[With regard to] a hole in the door: Its minimum size is that of a fist, the words of Rabbi Akiva. Rabbi Tarfon says: one handbreadth square. If the carpenter had left a space at the bottom or the top [of the door] or if one had shut [the door] but not closed it tightly, or if the wind blew it open, the minimum size is that of a fist. ⁴One who makes a place for a rod, for tongs, or a lamp, the minimum size is whatever is needful, according to the word of Bet Shammai. Bet Hillel says: one handbreadth square. [If it was made] for a peep-hole, for speaking through to his fellow, or for [human] use, the minimum size is one handbreadth square. ⁵The following [objects serve to] reduce [the area of a square] handbreadth:[A portion] of less than an olive-size of flesh [of a corpse] reduces [the opening for uncleanness that is] caused by a quarter of a kav of bones [from a corpse]; [A portion] of less than a barley-corn size of bone reduces [the opening for uncleanness that is] caused by an olive-sized portion of flesh; Less than an olive-sized portion of a corpse, Less than an olive-sized portion of carrion, Less than a lentil-sized portion of sheretz; Less than an egg-sized portion of food; Produce growing next to the window, A cobweb having substance; The carcass of a clean bird that he did not intend to eat, And the carcass of an unclean bird that had been intended [for food] that had not been rendered susceptible [to uncleanness], or which had been rendered susceptible [to uncleanness] but had not been intended [for food]. ⁶The following do not reduce [the area of the window]: Bone does not reduce [the area] for [other] bones; Nor [corpse] flesh for [other] flesh; Nor an olive-sized [portion] of a corpse; Nor an olive-sized portion of carrion; Nor a lentil-sized portion of reptile; Nor an egg-sized portion of food; Nor produce growing in the windows; Nor a cobweb having no substance; Nor the carcass of a clean bird which had been intended [for food]; Nor the carcass of an unclean bird which had been intended [for food] and had been rendered susceptible to uncleanness; Nor warp and woof threads that have negaim; Nor a brick from a bet haperas, the words of Rabbi Meir. But the sages say: the brick can reduce, because the dust [of the bet haperas] is clean. This is the general rule: what is clean reduces [the area], and what is unclean does not reduce it.