Ah, Houston, the birthplace of humidity! Notice the paper backed radiant barrier on the bat insulation covering the vaulted ceiling. It had become so fragile over time merely touching it would cause it to disintegrate! Looking down from the vault. The last time the homeowner had a new roof put on, they had a ridge vent installed as well. Notice the gap at the peak that allows air to continue through the vent unobstructed. The insulation had really settled in this 25 year old home.  Once you start seeing the top of the joists (the attic floor) it is probably time to add at least 6" of additional insulation. This was a hip style roof on this home...no gable ends. The vaulted ceiling, to the left, proved to be no problem!