Planking above scaffolds

50-77-103 . Planking above scaffolds. In buildings more than three stories high where persons are working on a scaffold or scaffolds on the outside of such buildings, such persons shall be protected by well secured planking set over the heads of such persons for the full width of the scaffolding on which they are working if another story or stories are being raised above such persons during the time they are working on such outside scaffold or scaffolding.