The home was built in 1900. Home has visible 1X wood in the unfinished attic.
Roof appears to be 2 layers of asphalt.
Is the roof decking(Sheathing) that is visible between the 1X a wood shingle roof?
The stated 13 year old roof did not look as it was installed properly. Looks like the 2nd roof or sheathing was deteriorated or buckling.