Rotten.

I’ve been waiting for a several weeks for a few days of reliably good weather so that I can re-roof the shed; today looks like the day to start. I was aware that rain was getting in, though when I came to rip off the old roofing felt it was in good condition. However, the chipboard underneath wasn’t.
 
There is now a plywood roof coated in bitumen adhesive underneath the new felt; that should keep the water out for a few weeks.