Reference for Bava Batra 13:2
אמר רב חמא בדינא קא מעכב והני מילי דלא מטו כשורי למטה מעשרה אבל מטו כשורי למטה מעשרה מצי א"ל למטה מעשרה רשותא דידי הוא ולא משעבד לך
to get in, and crawl on your belly to get out. Said R. Hama: He had a full right to stop him [rebuilding]. This, however, is the case only if the beams [of the upper room] did not sink lower than ten handbreadths [from the ground], but if they came as low as this, the owner of the lower room can Say: Below ten handbreadths is my property and is not subject to you.<span class="x" onmousemove="('comment',' And therefore I can demand to have the house pulled down and rebuilt. ');"><sup>2</sup></span>
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