Reference for Bava Batra 127:1
ואי סלקא דעתך בסתמא קני עומקא ורומא כי גבוה עשרה טפחים מאי הוי כיון דגבוה עשרה טפחים חשיב
Now if you assume that the space below and above is transferred automatically, what difference does it make if the parapet is ten handbreadths high?<span class="x" onmousemove="('comment',' That is to say, why should a roof with a parapet be different from a roof without a parapet (which is sold with the house), unless for the fact that the purchaser does not acquire the height automatically with the house. So Rashi. V, however Tosaf., s.v. htu'. ');"><sup>1</sup></span> — Since the parapet is ten handbreadths high the roof is reckoned as a separate structure.<span class="x" onmousemove="('comment',' And therefore is not sold automatically with the house. ');"><sup>2</sup></span>