I am in the process of replacing slates on my semi detached house. I have completed the back roof and the ladder seemed very secure and rigid, using a universal roof hook on my ladder, which goes over the ridge. But on the side roof, there is no ridge for the hook to go over. What is the best way to secure the ladder to the side roof? Should I remove some slates and tie the ladder to the rafters or is there perhaps another method that someone can recommend? I am using a roof anchor and full body harness (not forgetting the rope of course)