If asphalt shingles have been installed over wood shingles the next time they go to reroof will they have to remove both the asphalt and wood and install new sheathing?
Depends on the AHJ and the building dept regs. Some jurisdictions allow overlays.
Yes as two layers is the maximum permitted by the residential code unless you re-roof with standing seam metal.
do you have a picture of this roof? Asphalt DIRECTLY over wood shingle? Was it roll roofing or asphalt 3 tab shingle? How much did the wood shingles telegraph through?
Regardless of what code says, we’re running into more and more insurance companies stating asphalt / comp is to be installed over solid wood sheathing.
So it ends up being a tear-off and redo.
There was a time when roofers could get away with it and still get a permit, but I know Los Angeles will no longer issues permits for going over wood shingles, and I doubt OC will either.
Most jurisdictions will require the it be pulled off, and if the wood shingles were laid on spaced sheathing, or if for some other reason the old sheathing won’t meet modern requirements, the entire roof will have to be overlaid with a new roof deck.
It voids the shingle warranty too.
The last time I looked there is a map in the Code book showing the States that are considered the hail belt and it very clearly states one layer is all that is allowed and I am in the hail belt so when I see two layers I write it up;-)