The following laws apply when a functional window was closed entirely or closed to the extent that less than a handbreadth by a handbreadth remained. If it was closed with an entity that intervenes in the face of ritual impurity it is considered as closed, provided it is an entity that the owner does not intend to move. Therefore if he closed a window or reduced its size with foods that were not made susceptible to contract ritual impurity, they do not intervene. Even though they are not susceptible to ritual impurity and they are pure, his intent is to move them. If they were rotting, they intervene. Similarly, straw that is rotting intervenes. If it is not rotting, it does not intervene, because we assume that the owner intends to move it. When grain grew and blocked a window or reduced its size, it does not intervene, because the owner's intent is to remove it, lest it damage the wall. If its roots were distant from the wall, but the heads of the stalks grew on an incline and blocked the window, it intervenes. Similar laws apply in all analogous situations.
The following rules apply when a barrel that is filled with rotting dried figs which were never made susceptible to ritual impurity and are not fit to be eaten were placed in a window and the opening of the window faced a source of impurity. The barrel itself is impure, In such a situation, and similarly, if a container is filled with rotten straw that is not fit to be used as animal fodder, for mortar for building, or for kindling that was placed in the window: when the figs or the straw would be able to remain standing independently were their container to be removed, they would be considered as intervening. If not, they do not intervene. The following entities all reduce the size of a window: a) bitter grasses that are not fit for animal fodder, b) patches that are not three fingerbreadths by three fingerbreadths, that are filthy and firm, so that they are not fit to clean blood off a scratch, c) a limb or flesh that was hanging limply from an impure animal, provided the animal was lean and unfit to be sold to a gentile and tethered so that it will not flee, d) an impure fowl resting in a window, provided it is one which scratches, so that it would not be fit for a child to play with, e) a gentile who is bound, because he is one of the prisoners of the king whom another person may not release, f) an infant born after an eighth month pregnancy on the Sabbath, because it is forbidden to move him, g) salt that is mixed with thorns that is not fit to be used for food, nor for leatherworking, provided it is placed on a shard so that it will not damage the wall. The rationale is that these substances are not susceptible to ritual impurity, nor does the owner intend to move them, because they are not fit for work. Similarly, when a Torah scroll was worn out and placed in a window, if the owner had decided that it would be entombed there, it reduces the size of the window. In contrast, snow, hail, sleet, ice, and water do not reduce the size of a window, for they are susceptible to ritual impurity.
☀️ Skylight Rules
A skylight (arubah) in a roof creates a zone of purity directly below it (open to the heavens). If impurity is under the roof but not below the skylight: house is impure, skylight zone is pure. If impurity is only below the skylight: entire house is pure. If impurity is partly under roof and partly below the skylight, and the skylight is a handbreadth by handbreadth — the entire house and skylight zone are impure. If an olive is in a raven's mouth over a skylight — house is impure even without a cubic handbreadth.
If one reduced the size of the handbreadth with less than an olive-sized portion of the flesh of a corpse, less than an olive-sized portion of the meat of a dead animal, a portion of bone from a corpse that is less than the size of a barley-corn, or a portion less than a lentil from a crawling animal, these substances intervene in the presence of ritual impurity. The rationale is that they are all pure and since they are not important to the owner, he does not intend to move them. Similarly, less than an egg-sized portion of food that was not made susceptible to ritual impurity is not important, he does not consider moving it. Hence, all of the above reduce the measure of the handbreadth.
🏠 Stacked Structures
A house with a skylight, and a loft above with another aligned skylight: impurity in the house makes the loft impure (except under the skylight zone). Placing a pure-object susceptible to impurity over either skylight makes everything impure (it doesn't intervene). Placing a non-susceptible object over the lower skylight: house impure, loft pure. Over the upper skylight: house and loft both impure but everything above the upper skylight is pure.
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Bed Legs, Cracked Ceilings, and Combining Structures
If one closed a window with an earthenware vessel whose opening faced outward, it intervenes. The rationale is that it does not contract impurity from its outer side and thus it is pure. Therefore this earthenware vessel must be disgusting and perforated so that it is not fit to be used for anything, not even bloodletting, so that the person will not think of moving it.
The following laws apply if there was a corpse, a fourth of a kab of bones, or the like from bones that impart impurity through ohel in a house and the owner sought to reduce the size of the window of this house with a bone that is less than a barley-corn. Its size is not reduced, because the bone in the window is considered as part of the bones that generate impurity. Similarly, if a corpse or an olive-sized portion from the flesh of a corpse was in a home and the owner sought to reduce the size of the window with a portion of flesh from a corpse, its size is not reduced, because the flesh is combined with the other flesh. Nevertheless, a bone that is less than the size of a barley-corn reduces the size of a window and thus prevents the spread of impurity brought about by an olive-sized portion of flesh. And less than an olive-sized portion of flesh reduces [the size of a window and thus prevents the spread of impurity brought about by] a fourth [of a kab] of bones or the like. If one sought to reduce the size of a handbreadth with the woof and the warp of cloth that is afflicted with tzara'at or with a clod of earth from a beit hapras, its size is not reduced. The rationale is that an impure object does not intervene in the face of ritual impurity. If one made a brick from the earth of a beit hapras, it is pure and can reduce the size of a window. Our Sages' decree concerned only a clod of earth in its natural state. The following rules apply if the handbreadth was closed or reduced in size by a spider web. If its strands were substantial, it is considered as an intervening substance. If not, it does not intervene.
הלכה ו׳
🛏️ Structural Cases
Chipping a ceiling to insert a bed leg: if skylight is handbreadth-square, anything susceptible to impurity placed over it (like the bed leg) transmits impurity to the loft. If less than a handbreadth — loft is pure. A person placing their foot over a skylight creates a single ohel, combining impurity from below. Beams of house and loft aligned alternately: if each beam is a handbreadth wide, impurity only spreads to what is directly under the beam where it sits.
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🎓 Key Principles
Chapter 15
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Skylight Creates a Purity Zone A skylight in a roof creates a break in the ohel — the area directly below it is open to the heavens and thus pure, even when the rest of the house is impure.
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A Foot Unifies Two Structures Placing a foot over a skylight connects two otherwise separate zones into one ohel — any impurity in either zone then spreads to the combined structure.
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A Raven's Beak Suffices for Impurity Even without a cubic handbreadth opening, if an olive-sized portion is held in a raven's beak over the skylight's airspace, the house below becomes impure.
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Aligned Skylights Isolate Impurity Zones Aligned skylights in a house and loft create paired purity zones — impurity below one skylight goes straight up through the aligned openings without spreading to the sides.