704. More About Carmelis and Makom Patur

Shabbos 14:8

A place in the public domain that is exactly nine handbreadths high (about 27”) is part of the public domain regardless of its width or length because people commonly use it to arrange their burdens. If it is higher or lower than nine handbreadths, then: If it is four handbreadths by four handbreadths (about 1’x1’) or more, it is a carmelis (quasi-public domain). If it is less than four handbreadths by four handbreadths in area, it is a makom patur (exempt area).

Shabbos 14:9

If a roof is less than ten handbreadths high (about 30”) and is near a public domain so that people use it to adjust their burdens, it is prohibited to carry on the roof unless a ladder is permanently affixed to it. If such a ladder is attached, one may carry on this roof. If a pillar in the public domain is ten handbreadths high (about 30”) and four handbreadths by four handbreadths, it is considered a private domain. If a spike is driven into its side, even below three handbreadths high, it reduces the height of the pillar so that it is considered a carmelis. This is because objects may be hung from the spike or it may be used in other ways. Accordingly, the height of a pillar is calculated from its highest spike. This is so even if the pillar is covered with such spikes because things can be hung from them or they can be used in other ways.