Hi guys, the roof on my house was put on in August 2004, and I bought the house in June 2004. It is new 1/2 4 ply, no H-clips. The problem is that the plywood is severely dipping/buckling between the 24" OC rafters, and it needs fixed. The consensus among some contractors i have had on site, is that it is stemming from inadequate nailing and probably “blow through” from the air nailer.
One contractor is proposing to replace the really bad sheets, and then place another layer 1/2" 4 ply across the entire roof, to save on ripping off the old sheets. Is there any concerns with having two layers of plywood on the roof? He offers a 20yr warranty. (seams would be staggered so as to not line up).
Thanks for your help!