roof ladder on house   A clamp on roof hook should support a worker without a security rope. However occasionally a roof hook may ride up and off over the ridge during use, causing the ladder to slide off the roof. Having a rope tied to a secure object as shown can prevent this type of accident.
 Watch out for a bowed roof or a warped ladder. A roof hook with a large radius could be safer, but also heavier to handle   

Typical Roof Hook

 labeled roof hook