If one raised onto it a grapevine, a gourd, or ivy, and covered it with s’chach, it is invalid. But if the s’chach exceeded them, or if he detached them, it is valid.  This is the rule [regarding the validity of s’chach]: Whatever is susceptible to contamination or does not grow from the ground, we may not use for s’chach; but whatever is not susceptible to contamination and grows from the ground, we may use for s’chach.

Bundles of straw, bundles of wood, or bundles of fresh cane, may not be used for s’chach; but all of these are valid when they are untied.  All of them are valid for the walls.