Shulchan Arukh Orach Chayim · Siman 361

English

The law of a roof adjacent to a public domain. 2 sections: A roof adjacent to a public domain — within ten handbreadths and above ten handbreadths relative to a courtyard — since the public makes use of it, it is treated like a public domain, and the owner of the roof is forbidden to make use of it from his courtyard unless he makes a fixed ladder from his courtyard. What is a fixed ladder? Any ladder that is fixed there both for weekdays and for Shabbat.

English

A courtyard that was breached along its entire width or more than ten handbreadths into a public domain — the place of the former wall is treated like the sides of a public domain, which has the status of a karmelit, as does the courtyard itself. If it was breached at a corner, even less than ten handbreadths is forbidden. Similarly a house that was breached at a corner even less than ten handbreadths, and the roof was also breached until only a diagonal strip remains, is forbidden. But a breach that is not at a corner — we apply the principle that the edge of the roof descends and seals, even if the breach is more than ten handbreadths, provided the edge of the roof is not slanted, since then there is no effective edge. Rema: Some say we also require the roof to be four handbreadths wide. (Tosafot and Rosh, ch. Keitzad Mishtatfim, Semag, and Tur) We apply the principle that the edge of the roof descends and seals even with two walls, if there are two complete walls joined together — but two walls facing each other, no. (Tur)