My condo is planning to replace our roof because the original was installed entirely incorrectly. The original roof appears to be a single layer modified bitumen roof, but it began to fail within 6 months causing dozens of leaks into the units. We have a flat roof (with a slope for water runoff) and wooden roof decks on top. Photos at the link below:
Our roofer recommended adding another layer of modified bitumen on top of the existing faulty layer, and he says that this will create a 2 layer modified bitumen roof that should last for 20+ years. Specifically, we are looking at adding Firestone APP UltraWhite cap sheet.
So, my question: Is it a good idea to just add a second layer of modified bitumen to an existing faulty layer and expect it to have the life of a 2 layer modified bitumen roof? Do we need to ensure that there is some sort of protective liner underneath the original layer to ensure the new roof will be properly installed?
Thanks in advance for any feedback!