I do not really understand the question, are you referring to the overlap? From osha:3' may have been one of the answers. thanks.
The answer must have been in the 'Code of Federal Regulations' which I do not have.
damn i am dense this morning, i completely misread the question.:slaphead:OSHA 1926.1053(b)(1)
When portable ladders are used for access to an upper landing surface, the ladder side rails shall extend at least 3 feet (.9 m) above the upper landing surface to which the ladder is used to gain access; or, when such an extension is not possible because of the ladder's length, then the ladder shall be secured at its top to a rigid support that will not deflect, and a grasping device, such as a grabrail, shall be provided to assist employees in mounting and dismounting the ladder. In no case shall the extension be such that ladder deflection under a load would, by itself, cause the ladder to slip off its support.