8.In many places, it is common for a roof to extend beyond the wall of a
house and project into the street, where it is supported by pillars. In
such an instance, it is forbidden to take objects from the house to the
area [under the extended roof], or to take objects from there into the
house. Similarly, it is forbidden to carry an article a distance of four
"amos" (1) within that area [under the extended roof], because it is
governed by the same laws as the street [in front of it], and therefore
could either be a public domain ("reshus harabim") or a "Carmelis,"
depending on the halachic status of that particular street.
Although the roof is supported by pillars and with them forms a "tzuras
hapesach" ("shape of doorway"), which is halachically equivalent to a
partition ("Mechitzah"), there are no partitions on either side, [and
therefore it is not considered to be a completely enclosed private domain
within which one could carry]. [To turn the area under the extended roof
into a private domain,] it is necessary to erect a pole at one end [of the
wall facing the street], such that it is directly opposite the [last]
pillar supporting the roof [on that side], thereby creating a "tzuras
hapesach" [from the side]. The same should be done at the other end [of
the front wall of the house].
If several houses [with extended roofs] are lined up next to each other, it
is sufficient to erect one post at both ends of the row (that is, at the
edge of the corner house on either side); [in that situation] the families
are required to make an "eruv chatzeros" (2)
(1) Opinions among the authorities as to the exact length of an "Amoh"
("cubit") range between 48 and 60cm (20 to 24 inches).
(2) "Eruv chatzeros" literally means "conglomerate of courtyards"; in the
days of the Talmud, it was common for a number of private homes to share
one enclosed courtyard; a properly enclosed courtyard is defined as a
private domain, and thus it would be Biblically permissible to carry from a
private home into the shared courtyard. However, the Sages feared that if
people would be allowed to carry from a home owned by one individual, into
a courtyard shared by a number of individuals, then people may mistakenly
believe that it is permitted to carry from a private domain into a public
domain, and vice versa. Therefore, the Sages prohibited carrying between a
private home and the shared courtyard in which it is situated. Now, in
order to permit carrying between the houses and the courtyard, a loaf of
bread has to be collected from each house in the courtyard, and then all
the loaves have to be placed in one of the houses for the duration of
Shabbos. This then symbolizes that all the contributing residents are
legally residing in one dwelling (the house where they left their bread).
In this way, the courtyard can be viewed as the province of only one
dwelling, rather than several, and since the houses and the courtyard are
both the property of a single consortium, there is no prohibition to carry
from one to the other (because it can no longer be viewed as carrying from
a private area to a "public" area, and the potential error which prompted
the original rabbinical prohibition would not occur). This whole procedure
is called "Eruv Chatzeros."
In our halacha above, the roofed area in front of the row of houses is
considered the equivalent of the type of courtyard discussed in the
previous paragraph, and therefore requires an "eruv chatzeros."