Working on reshingling my roof. The roof deck turned out to be 3/8" plywood which is starting to break down due to the number of times the roof has been replaced.
The deck is not rotting out except for a few spots along the drip edge, which we are cutting out to replace. The main issues are that you can hear the plywood cracking and feel it give under you as you walk around. There have been several times we were afraid we were going to put a foot through it, though it has not happened yet.
The question is, can we just lay a second layer of sheathing over the existing deck to stiffen things up? We are thinking of nailing 7/16" OSB over the existing plywood and making sure the the joints between the layers do not line up.
Anyone aware of code or other issues inherent in this approach? I have not been able to locate anything that addresses this point.
We are located a bit south of Saint Louis, roof pitch is 5 in 12 if that makes a difference.
Best Answer
It hard to say without seeing the structure but it sounds like the decking was under engineered for the weight of asphalt shingles to begin with. You could put the OSB overtop but by the time, you clean that surface up (pull nails, etc) and adhere the new surfaces together, you might as well strip it.
You're also leaving extra weight on the roof and if you are already feeling degradation between the rafters, you may ultimately end up with the same problem just thicker.
If you are going to go with asphalt, you might want to upgrade to at least 7/16th OSB depending on your rafter spacing.