We have a significant amount of water damage from leaks in the roof. That has caused some damage all the way through the three floors. Fortunately, the damage on the first (retail) floors is minimal. But to work on the upper floors, I had to take up the rotten floors--didn't feel like plunging 30 ft. through the beams.
Like a lot of this project, there's a whole series of short-term steps, e.g. building stairs, fixing the floor, etc. that are needed to actually do the major work.