chalet re-roofing

hey guys,

i'm trying to find out some information. i have a re-roofing job coming up on a 30+ years chalet and need to know what the sub roofing is under it. i can tell you that it's not plywood. it feels like some kind of sub-roofing/insulation together with felt paper and shingles over it. it's the original roof and the owner wants plywood installed before i install the new shingles.

can i plywood over this or if i rip it up will i be staring inside her house as it is an open beam ceiling chalet. i don't think they want to be staring at plywood from inside the house. anyone with info would greatly help. thank you