Yerushalmi Bava Batra 3:9 ירושלמי בבא בתרא ג׳:ט׳

MISHNAH: A protrusion¹³²An extension of the roof protruding outside the wall of the house. If it is built over a neighbor’s courtyard and extends from the roof at least by one handbreadth, the neighbor may forbid it but if it was built without objection it cannot be challenged later. If it extends less, the neighbor cannot object but does not have to take it for granted; he may build a new wall incorporating the molding. down to one handbreadth establishes a right of possession but he can object; less than a handbreadth does not establish a right of possession but he cannot object.

HALAKHAH: “A protrusion down to one handbreadth establishes a right of possession,” etc. Rebbi La in the name of Rebbi Yannai: If the molding is [up to] one handbreadth wide he may extend it all the way, to draw it all the way¹³³The inserted word is from E. It seems to mean that if a house was built with a protruding mold along part of the wall with the neighbor’s acquiescence, the protrusion can be extended along the entire length of the wall without requiring a new permit.. Nathan¹³⁴Correct in E: R. Nathan in the name of R. Hoshaiah., Rebbi Hoshaia: About one who divides his house¹³⁵It seems that this sentence belongs to the next Halakhah, where it is explained that a person may transform a one-family house into a multi-family one as long as he constructs an interior staircase and does not increase the number of doors leading from the house into the courtyard..