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When a projection protrudes from the side of an entrance to a home facing downward and it is twelve handbreadths or less above the earth, it conveys ritual impurity regardless of how small it is. It is clear that such a conveyance of impurity is merely a Rabbinic ordinance. Similarly, any analogous instance where impurity is conveyed by something that is not a sturdy ohel is only a Rabbinic ordinance.
Projections that are more than twelve handbreadths high or which face upward and similarly, the crowns and the ornamental embellishments that project from a structure, do not convey impurity unless they are a handbreadth by a handbreadth in area. This also applies to a projection that extends over an entrance from a lintel. Even if there was a reed at the side of the lintel as wide as the entrance, it does not convey ritual impurity unless it is a handbreadth by a handbreadth in area.

When a projection surrounds an entire building and encompasses a handbreadth at the entrance to the house, it conveys ritual impurity. If it encompasses less than a handbreadth at the entrance of the house and there is impurity in the house, keilim under it are impure. If there is impurity under it, it does not convey impurity to the house. Similar laws apply with regard to a courtyard that is surrounded by an exedra.

When a window serves a functional purpose and a projection protrudes across the entire window, even if it was only as wide as a thumbbreadth, it conveys ritual impurity. This applies provided it is two fingerbreadths or less above the window. If it is more than two fingerbreadths higher than the window, it does not convey ritual impurity unless it is a handbreadth wide. When there is a projection over a window that is made for light, it conveys ritual impurity regardless of its size and regardless of its height.
When there is a structure that protrudes in front of a window upon which a person looking out from the window leans while looking, it does not convey ritual impurity. If it has a projection over it, we consider the structure as if it does not exist and the projection above it conveys ritual impurity.
How do all these projections convey ritual impurity? If there was impurity under them or under the house, everything is impure - whether it is in the house or under the projection.

When there are two projections one on top of the other, each one of them is a handbreadth by a handbreadth in area, there is a handbreadth of space between them, and there is impurity below the lower one, only the space below it is impure. If there is impurity between them, only the space between them is impure. If there is impurity above the upper one, the space above it until the heavens is impure.
If the upper one extended beyond the lower one for a handbreadth and there was impurity below the lower one or between them, the space beneath them and between them is impure. If there is impurity above the upper one, the space above it until the heavens is impure.
If the upper one extended beyond the lower one for less than a handbreadth and there was impurity beneath them, the space beneath them and between them is impure. If the impurity was between them or under only the extra portion of the upper projection, the space between them and under the extra portion is impure, but the space below the lower projection is pure.
If each of the projections were a handbreadth by a handbreadth in size, but there was not a handbreadth between them, and there was impurity below the lower one, only the space below it is impure. If there was impurity between them or on top of the upper one, the space directly above it until the heavens is impure.
If the projections were not a handbreadth by a handbreadth in size, whether there was a space of a handbreadth between them or not, whether the impurity was beneath the lower one, between them, or on top of the upper one, the impurity pierces through and ascends and pierces through and descends, because it is flush. Similar laws apply when there are two curtains that are a handbreadth above the ground and placed one on top of the other.
When there are keilim, garments, or wooden tablets placed on top of each other and impurity was flush between them, if the impurity was a handbreadth above the earth, the k'li that is above it is considered as creating an ohel over the space of a handbreadth and it imparts impurity to all the keilim under it. If there were stone tablets, even if they were a thousand cubits above the ground, the impurity pierces through and ascends and pierces through and descends, because they are considered as earth.

When tablets of wood are touching each other at their corners, they are a handbreadth above the ground, and there is impurity under one of them, the keilim which are under the second are pure, because it is not touching the other one over the space of a handbreadth. A person who touches the second tablet is considered as one who touched keilim that touched a covering over a corpse.
Different rules apply, by contrast, with regard to all those keilim which we said convey ritual impurity and do not intervene in the face of it. If such a k'li was positioned above a corpse, all of the keilim that are above it are impure, as we explained. They are deemed impure as keilim that were held over a corpse. Even the keilim over it that are not directly over the impurity are impure. They are considered keilim that touched keilim that were held over a corpse.

When an earthenware jug was standing on its base in open space and there was an olive-sized portion from a corpse inside of it or below it, directly below its inner space, the impurity pierces through and ascends, pierces through and descends. The jug is impure, because the impurity pierces its bottom and its inner space becomes impure.
If the impurity is located under the thickness of its walls, the impurity pierces through and ascends, pierces through and descends, but the jug is pure. Why is the jug pure? Because the impurity does not pierce through into its inner space, but only to its walls and an earthenware container contracts impurity only from its inner space.
If some of the impurity was below the thickness of its walls and some below its inner space, the impurity pierces through and ascends, pierces through and descends. If the walls were a handbreadth in thickness, it is entirely impure but the space aligned with its opening is pure, for the impurity has spread only throughout the walls.
When does the above apply? When the jug was pure. If, however, the jug was impure, it was a handbreadth raised above the earth, it was covered, or it was turned upside down, and the impurity was in it or on top of it, everything is impure and anything that touches it in its entirety is impure. If it had a cover fastened to it and was placed over a corpse, any food and drink inside of it are pure, but the keilim over it are impure.
When jugs are resting on their bases or leaning on their sides in open space, they touch each other over a handbreadth of space, and there is impurity below one of them, the impurity pierces through and ascends, pierces through and descends, because it is flush.
When does the above apply? When the jugs are pure. If, however, they are impure or they are raised a handbreadth above the ground, and there is impurity under one of them, the space below all of them is impure, because they are considered as a single ohel.