@IslandRoofing wrote:
I wouldn't say that you "have" to replace it. With the amount of overhang you have it should be protected from most rain. With that said I would most certainly replace if it was my house. Also when doing a quote I would bring it to the attention of the homeowner and let them decide if they want it replaced or not. Its a much more of a pain doing it after the roof is replaced as opposed to doing it while doing the roof replacement.
In regards to osb vs cdx its pretty much "Chevys and Fords". Older guys always swear by cdx, however I feel the cdx of today isn't up to the standards it was 20 years ago. Pretty much if either gets wet repeatedly you will have problems. Osb will swell up when it gets wet and cdx will warp and delaminate when it gets wet, so you can pick your poison. Osb will rot quicker if exposed to the elements though.