You can walk on a precarious surface. A successful check lets you move at half your speed along the surface for 1 round. A failure by 4 or less means you cant move for 1 round. A failure by 5 or more means you fall. The difficulty varies with the surface, as follows:
None. A Balance check doesnt require an action; it is made as part of another action or as a reaction to a situation.
Armor Check Penalty