[Avodah] home depot mats

[M Cohen]

.. Why should there be a difference if the schach is parallel or
perpendicular to the support beams? 

If it's parallel, then the strings holding the slats together are holding up
the slats
If it's perpendicular, then the beams below are holding up the slats

I assume the strings are posul as a maamid (at least m'drabban)
Ie synthetic strings (posul for schach d'orisa) or cotton strings (posul for
schach m'drabban - nishtaneh)

mc