747. Beams That Do Not Connect

Shabbos 17:24

What if a beam protrudes from one wall of an alley but does not reach the opposite wall, or if a beam protrudes from one wall and a second beam protrudes from the opposite wall? In such a case, if the beams reach within three handbreadths of one another, it is sufficient. If there is a gap of more than three handbreadths between them, another beam must be brought.

Shabbos 17:25

Similarly, if two beams run parallel to one another and neither of them can support a brick of the requisite size by itself, one need not bring another beam if the two beams together can support the brick. If one beam is situated higher up than the other, we treat the higher one as if it were lower and the lower one as if it were higher (i.e., at the same level) so long as (a) the higher beam is not above 20 cubits (35’), (b) the lower beam is not below ten handbreadths (30”) and (c) there would be less than three handbreadths (9”) between the beams if they were on the same level.