Pi Tikra Yored v'Sosem – Eruvin 25b

Pi Tikra Yored v'Sosem – Eruvin 25b

The Gemara here introduces the concept of “pi tikra yored v'sosem” (literally: the lip of a roof comes down and closes; see also 94b). The principle, as defined in the Shulchan Aruch,(Orach Chaim, 361:2), is that, when a roof is at least four tefachim by four tefachim and set atop two complete walls, we view the thickness of the roof as an imaginary wall for the remaining two sides. (To employ the principle of pi tikra the structure must have two walls adjacent to each other connecting at a corner, not two parallel walls, see Rama, Shulchan Aruch, Orach Chaim 361:2).

In one of the early works on eruvin in modern cities, the Tikvas Zecharia, Rabbi Zecharia Rosenfeld, the first Chief Rabbi of St. Louis, notes that telegraph poles often support a thicket of wires at their tops. These wires are well within three tefachim of each other. Viewing them, halachically, as connected, allows one to consider the thicket as a roof. One could then apply the principle of pi tikra yored v’sosem to them. In practice, however, Rabbi Rosenfeld does not utilize this approach in sanctioning the use of the telegraph poles and wires as halachic walls, preferring instead the already accepted trend to view them as comprising tzuros ha'pesach. He does, however, propose that the presence of these “roofs” along the length of a street will diminish their potential to be regarded as a reshus ha'rabbim, since roofed over reshuyos ha'rabbim are automatically downgraded to carmelis status. - see Nesivos Shabbos 3:1 and note 6, where he considers (inconclusively) how much of a roof is necessary to negate a reshus ha'rabbim.

1.

1Eruvin 94b.