House is 40 yrs old roughly there are three layers on the roof 3 tab asphalt. 3/8th sheathing plywood underneath a roofer told me that because of so many layers too many nail holes so I need to replace all sheathing with 5/8th on the whole house been in the house 16 yrs lost some shingles so i want to replace the roof do I have to replace all wood or just any i find that has water damage. Please advise
Roofer is trying to rip you off with the story about too many holes... or he doesn't know his stuff. Trusses are filled with mostly empty space yet they still are strong. As long as there is wood around the holes all the molecules of wood will connect to form a "holy" truss.
3/8" plywood is really weak but I have seen a few houses built with it. Instead of ripping off all the wood, install 1/2" on top of that. 1/2" is cheap because it's very common and a lot is sold. 1/2" PLUS 3/8" will be VERY strong and you can jump on it and it would give at all. Since the rafters are covered with the 3/8 you have to find them and try to nail the 1/2" thru the 3/8" into the rafters. You can't nail to the 3/8 or the nails won't hold. Nailing into the rafters will be strong or you can screw it in is even better. This will save you all the labor of ripping off the old wood, it will save on cheaper plywood to buy and it will be strong.