1x12 roof decking
In 2008 we had a new shingle roof installed over 1 x 12 sheeting from original construction in 1959. Repair was required in a small area but otherwise the 1x12s were determined to be in good shape. Over the past 10 years there have been multiple leaks with some bad enough to lead to significant ceiling damage and industrial fans from Serv-Pro brought in for drying - 6 different rooms involved. Several areas have been reshingled to address leaks- some worked, some have not. Now contractor (who brought in a relative who has been in construction > 30 years) says problem is cupping of the 1 x 12s is problem allowing water to be blown under raised shingles creating leaks. Would cupping occur in this age wood unless there was water getting to wood from exterior? Should the 1x12 been ripped to 1x6 before new shingles were applied?