931. A Trench Between Courtyards

Eiruvin 3:11

If a breach in the wall between courtyards is smaller than ten cubits wide (about 15 feet) and the residents want to extend it to ten cubits, they must excavate a section of the wall ten handbreadths tall (about 30") to enable them to make a single eiruv. Optimally, if they want to make a breach larger than ten cubits in a wall, it should be as high as the height of the average person.

Eiruvin 3:12

If there is a trench between two courtyards that is at least ten handbreadths deep (about 30") and at least four handbreadths wide (about a foot), the residents must make two separate eiruvs. If the trench is smaller than this, they may only make a single eiruv and not two eiruvs. If the depth of the trench is reduced by filling it with dirt or pebbles, the residents may only make a single eiruv and not two eiruvs because the assumption is that the dirt or pebbles were intended as a permanent addition to the trench. However, if the trench was reduced by filling it with straw or hay, it is not significant enough to be considered a permanent addition without specific intention to that effect.