Reference for Bava Batra 118:4

לימא בהיזק ראיה קמיפלגי דמר סבר שמיה היזק ומר סבר לאו שמיה היזק

IF IT IS LESS THAN A HANDBREADTH THERE IS NO <i>HAZAKAH</i> FOR IT AND HE CANNOT PREVENT IT [FROM BEING MADE]. R. Huna said: This only means that the owner of the roof cannot prevent the owner of the courtyard [from using it],<span class="x" onmousemove="('comment',' Although it is his property, because the owner of the courtyard can at any time tell him to remove it. ');">³</span>

Jastrow