714. Projections Extending from a Wall

Shabbos 15:4

Let’s say that some object projects from a wall near a window. If this projection is more than ten handbreadths from the ground (about 30”), it is permitted to use from the window because the public domain only extends ten handbreadths from the ground. Therefore, one may use the entirety of a wall except for the bottom ten handbreadths.

Shabbos 15:5

The rule stated in 15:4 applies when there is only one such projection. If there are two, one above the other, there are different rules even though they are both higher than ten handbreadths from the ground. If the upper projection is four handbreadths by four handbreadths, it may not be used because it is its own domain, as is the projection below it. Accordingly, each one prohibits the use of the other because the residents of two different domains cannot use the space of a single domain.