Some manufacturers do include a "recommendation", usually 3/8 plywood, 7/16 osb or equivalent. That is easy enough to determine. The pickle I find myself in is in the word "solid". Case in point: I was scheduled to conduct a final roof inspection but when I arrived I was asked to evaluate the sheathing. The existing shingles had been removed and the house was tarped. The contractor and homeowner wanted me to cite the sheathing so the insurance company would cover it. Right or wrong I try to stay out of that type of transaction, and tried to avoid getting involved in this one. I advised them that if I make that call it is irrelevant who covers it or who pays for it. I explained that often I experience "soft" decking after the shingles are installed and that as long as the roof holds my concentrated load it is not an issue. This has been the practice of the departments I have worked in out here and frankly most homeowners would go ballistic if I mentioned replacing the roof sheathing. Well, they insisted so I did go up and I found that it was indeed bad, the worst I have seen. So I wrote a correction. Subsequently I received a call from the insurance adjuster who also observed the roof and agreed. Today I got a call from the homeowner saying the insurance company won't cover it as it is considered normal wear and tear on a 30 year old structure. I told them that they now are the proud owners of a correction to replace the unserviceable sheathing and as I had stated already, it didn't matter who pays for it. This was just a reminder for me that I don't really have a consistent practice for when a roof deck must be replaced. Probably half of the roofs I inspect are on homes that were sheathed 30 years ago and if the truth be known probably wouldn't pass the "solid" criteria today. So I am curious about what others experience and how they handle it. FYI, a tremendous hail storm came through a couple of months ago and as a result thousands of roofs are being replaced right now. We get the decking question pretty often.