Different roof types fail at differing rates and with different failure modes. Without going into a long dissertation, the several general failure clues are:
- Does the roof leak in numerous locations?
- Do leaks continue, despite repeated repair attempts?
- Do repairs seem to make leaks worse, or do new leaks develop after repairs?
- How tolerant is the occupancy to leaks? Low leak tolerance generally means the “failure” decision is reached earlier. It is generally better to re-roof at the appropriate juncture, rather than pouring money and time into ill advised repairs, but there are exceptions.