Reference for Bava Batra 12:6

אמר מר זה עושה מעקה לחצי גגו וזה עושה מעקה לחצי גגו זה שלא כנגד זה ומעדיף פשיטא

Abaye said: If there are two houses on opposite sides of a public thoroughfare, the owner of the one should make a parapet for half his roof, and the other a parapet for half his roof, in such a way that the parapets do not face one another,<span class="x" onmousemove="('comment',' E.g., if one builds on the north side, the other should build on the south. ');">⁹</span> though each should extend [his parapet a little beyond the middle].<span class="x" onmousemove="('comment',' To avoid the possibility of 'overlooking'. ');">¹⁰</span>

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