Ohalos, Chapter 14, Mishnah 1. Picture yourself standing at the front door of a house. In many homes a modest roofing of some kind has been built out over the entrance, and it earns its keep: in the rain you have a dry spot to shake out and fold your umbrella, you can rest your bags on the ground while you hunt for the key, and beyond all of that it lends the entrance a finished, handsome look. That very sort of overhang is the subject of our mishnah, and the issue before us is whether tumas meis resting under it is pulled into the house.
The Ziz
The mishnah calls this projection a ziz. It is a small ledge jutting out from the wall above the doorway, and it may be built of wood or of stone. Like many awnings, it does not simply stick straight out; it extends outward and then bends downward, forming the shape of the letter L.
Says the mishnah: "haziz mevi es hatumah kolshehu." If there is tumas meis underneath this ledge and the door of the house is open, the tumah is brought inside, and this is true "kolshehu," no matter how small the ledge is. Even if it protrudes from the wall less than a tefach, the house becomes tomei.
This demands an explanation. Until now we have been taught over and over that an ohel requires a tefach. Why should this little ledge be different? The answer is that the ziz is not an independent covering at all; it is part of the doorway itself. Whether it was built to shelter the person standing at the entrance or simply to beautify the entrance, it belongs to the doorway, and therefore it does not need its own tefach. It is treated as though it already has a poseiach tefach.
The Bartenura adds a further point. Precisely because the ziz has this L-shape, first extending outward and then turning downward, we view it as though it descends all the way to the ground, so that it is literally a continuation of the doorway. The mefarshim offer a number of different approaches in explaining what the Bartenura intends here, but that is his language.
Gizra and Gavlis
The mishnah continues: "hagizra vehagavlis biposeiach tefach." These are two other kinds of overhangs, and their halachah is not the same as the ziz. The ziz needs no tefach, but the gizra and the gavlis bring tumah into the house only if they measure a tefach by a tefach, for only then are they an ohel in their own right.
Where does the distinction lie? The mishnah supplies its own definitions for the first two: "eizehu haziz shepanav lematah, vehagizra shepaneha lemaalah." The ziz, the one that conveys tumah indoors even when it measures less than a tefach, is the overhang whose face is turned toward the ground: it juts forth from the wall and its outer edge angles down. The gizra is fashioned in the very same L-form, projecting from the wall and bending at its edge, except that its face is turned skyward instead.
The reasoning is easy to follow. An overhang whose edge angles downward is obviously in the service of the entrance: it covers whoever is standing there, and it gives the doorway a completed appearance. Turned the other way, it is nothing more than a shelf. Maybe someone keeps flowerpots on it; who can say. Whatever purpose it serves, it does not become an extension of the doorway and it is not automatically annexed to it. And so, short of a full tefach in each direction, it conveys no tumah indoors whatsoever.
And the gavlis? Picture the upper contour of the letter ches: level and straight along the middle, with each of the two ends bending toward the ground, yet nothing running down to the floor as a support. That is the gavlis over an entrance, and it too requires a tefach in each direction. On first hearing this is puzzling, for those two descending ends give it the appearance of belonging to the doorway. The mefarshim resolve it: since the whole stretch in the middle is level and bare, with nothing dropping down from it, its nature is that of a shelf and not of an extension of the entrance. Only the ziz, whose entire width projects out and then angles downward, is genuinely constructed to cover the one who enters, and only it merges into the doorway.
How High May the Ziz Be?
One further limitation attaches to the halachah of the ziz. The mishnah inquires: "ubameh amru" - regarding which case was this taught, that a ziz conveys tumah kolshehu with no requirement of a tefach in each direction? Comes the answer: "biziz shegavoah min hapessach shelosha nidbachin sheheim shneim asar tefach."
Nidbachin means rows of building stones or bricks. The ziz may sit no higher than three such rows above the doorway, and since each nidvach is four tefachim high, that comes to twelve tefachim.
"Yoser mikan, mevi es hatumah biposeiach tefach." If the ziz is more than twelve tefachim above the top of the doorway, then even though it is built in the downward-turning L-shape of a proper ziz, it brings tumah into the house only if it measures a tefach by a tefach. Once it is that high, it is no longer joined to the doorway, and it must therefore qualify as an ohel on its own.
Ataros and Pituchin
The mishnah concludes with two more features found over doorways: "ha'ataros vehapituchin mevi'in es hatumah biposeiach tefach." An atarah means a crown, and here it refers to a rounded, dome-like form built over the doorway, curved like the letter C, somewhat resembling a crown. Pituchin are carved designs worked into the stone above the doorway. These are built for beauty, and at times they project outward a tefach or even more.
The ruling of the mishnah is that these two do draw tumah into the house, but only where they measure a full tefach in both dimensions. Since their purpose was never the entrance but rather the adornment of the building, they are handsome indeed, yet the doorway is not regarded as extending outward by means of them. They will therefore convey tumah inside only by qualifying independently as an ohel of a tefach in each direction.
Reviewing the Mishnah
An overhang above an entrance that projects from the wall in an L-form, running outward and then angling downward, conveys tumah lying beneath it indoors even when its projection is minimal, narrower than a tefach. It merges with the entrance and is reckoned a piece of the doorway, so that tumah beneath it stands like tumah beneath the doorway itself, which travels into the house.
This applies only when the ledge is not more than twelve tefachim above the doorway. From twelve tefachim and higher it is no longer part of the entrance. And it applies only to this particular shape. If the projection turns upward, or if it curves downward at the sides but runs flat across the width of the doorway, a tefach is required. The same holds for a decorative crown or engraved stonework: those are made to beautify the house, not to serve the doorway, and unless they protrude a full tefach they bring no tumah inside.
This is the Bartenura's pshat in the mishnah. The Rambam explains it differently, and it is well worth looking into the mefarshim printed alongside the Mishnayos to see his approach. "Ten lechacham veyechkam od."