Bava Batra 59B

ויכול למחות. פחות מטפח ⁠– אין לו חזקה, ואין יכול למחות.

and the owner of the courtyard can protest its construction. If it protrudes less than a handbreadth, the owner of the house has no means to establish an acquired privilege for its use, and the owner of the courtyard cannot protest its construction.

גמ׳ אמר רבי אסי אמר רבי מני, ואמרי לה אמר רבי יעקב אמר רבי מני: החזיק בטפח ⁠– החזיק בארבע. מאי קאמר? אמר אביי, הכי קאמר: החזיק רוחב טפח במשך ארבע ⁠– החזיק ברוחב ארבע.

Talmud: R' Asi says that R' Mani says, and some say that R' Ya’akov says that R' Mani says: If one established an acquired privilege with regard to a projection of a handbreadth, he has established an acquired privilege with regard to 4 handbreadths. The Talmud asks: What is he saying? Abaye said that this is what he is saying: If one established an acquired privilege with regard to a projection that measures one handbreadth wide by 4 handbreadths long, he has established an acquired privilege with regard to extending the projection to a width of 4 handbreadths.

פחות מטפח ⁠– אין לו חזקה, ואינו יכול למחות. אמר רב הונא: לא שנו אלא בעל הגג בבעל החצר, אבל בעל החצר בבעל הגג ⁠– יכול למחות. ורב יהודה אמר: אפילו בעל חצר בבעל הגג, אינו יכול למחות.

The Mishnah teaches that if the projection protrudes less than a handbreadth the owner of the house has no means to establish an acquired privilege for its use, and the owner of the courtyard cannot protest. Rav Huna says: They taught only that the owner of the roof cannot protest the actions of the owner of the courtyard, i.e., he may not demand that the owner of the courtyard refrain from construction that interferes with the former’s use of the projection. But the owner of the courtyard can protest the actions of the owner of the roof, and demand that the latter not build a projection of any size, even less than a handbreadth. He can also demand that the owner of the roof not use an existing projection, since it leads to damage caused by sight. And Rav Yehuda says: Even the owner of the courtyard cannot protest the actions of the owner of the roof.