1,305. An Overhanging Roof

202:4 The halacha discussed in 202:3 is true even if the roofs of the adjacent houses are not level, one being higher than the other. Even if the roof of the house where the impurity resides is much higher than that of the other house, or vice-versa, we have a received tradition from Moshe at Sinai that we treat the higher one as if it were brought down to the lower one. If doing so would cause the roofs to touch, then the impurity is transmitted from one to the other. However, if there is gap of whatever size between them, then the impurity is not transmitted

202:5 Similarly, if there is a beam across an alley, as is done when making an eiruv, and it's one handbreadth wide, and the roofs overhang its length a handbreadth on one side and a handbreadth on the other side, then the impurity is transmitted from under the roof to under the beam, and it is transmitted in turn under the roof of the house on the other side. The ritual impurity will spread anywhere there is a canopy the size of a handbreadth until there is a gap. (A handbreadth is about three and a half inches.)

The law is the same when there is an arch between two houses, built as is done for courtyard gates (i.e., the ends of the arch are connected to the houses). Even though there's no projecting roof over this arch, the impurity is nevertheless transmitted from under the roof of the house to under the arch. Sometimes, however, an arch is made with legs going from the ground up; when this is the case, there is a barrier between the walls of the house. In such case, if the edge of the roof doesn't project and the barrier on one side extends further than the roof above it, then there isn't anywhere for the impurity to go because there is a gap with no canopy.

Sometimes there is a wall between two houses that has no opening but there is a roof extending above it. In such a case, the impurity goes from one roof to the next. This situation can be rectified when necessary by removing the roof tiles in one spot so that there will be a gap of a handbreadth without any canopy. One must check that there isn't anything projecting a handbreadth from the wall itself, since they often build walls protruding.