727. Reducing the Size of an Enclosure

Shabbos 16:8

If an enclosure is larger than necessary to plant two seah of seed, so someone tries to reduce the area by planting trees, the enclosure is not considered reduced. If one installs a pillar ten handbreadths tall (about 30”) and at least three handbreadths wide (9”) next to the wall, the enclosure is effectively reduced. If the pillar is less than three handbreadths wide, the enclosure is not considered reduced because something within three handbreadths of an existing structure is considered part of that structure. Similarly, if someone erects a partition more than three handbreadths from the wall, he has effectively reduced the enclosure; if the partition is within three handbreadths of the wall, he has accomplished nothing.

Shabbos 16:9                                    

Cement applied to the wall serves to reduce an enclosure even though cement is insufficient to be considerate a structure in its own right. If an area larger than needed to plant two seah is located on top of a mound and one builds a wall on the edge of the mound, he has accomplished nothing because a partition on top of a partition is of no significance. If a wall was built on top of a wall, then the lower wall sunk into the ground but the upper wall remained, then if the upper wall was built to serve as part of a dwelling, since it is the only wall now visible, it is considered significant and one may carry throughout the enclosure because of it.