Proper site preparation prevents roof sagging, twisting, and long-term performance issues.
Historic materials, period construction methods, and heritage considerations all differ significantly.
If you installed an ice barrier, the felt paper goes on top of that; otherwise, it goes directly on the decking.
To sum up the difference between flat roofs I have compiled a scoring system out of ten for domestic properties, 10 being the best and 1 the worst.
Some old roofing material could fall during this stage, and this could be dangerous.
You can decrease the risk for them and others by completely covering the shingles rash, washing your hands frequently, confirming they have had the varicella vaccine (if indicated for them), and avoiding skin-to-skin contact.