One may only use sechach which has grown from the ground (gidulei karka), is detached from the ground, and is not susceptible to impurity (eino mekabel tumea). Zip ties are generally made from a material which one may not use for sechach. One should not support sechach with a material which cannot be used for sechach. This principle is known as "ma'amid bedavar hamekabel tumea." If the sechach can stay down in a normal wind (ruah mesuya), and the zip ties are only used to ensure that the sechach does not move out of its place in a gust of wind (ruah she'eina mesuya), then zip ties may be used. If, however, zip ties are used to hold down the sechach and ensure that it does not move from its place even in a normal wind, then one cannot use zip ties to secure the sechach.