I live in a frame with 26 ft ceiling at the peak and the walls leading up to the peak also serve as my interior walls. The attic under the peak also is floored and I can stand erect in this area. Very little insulation in the attic and a light coating in the exterior walls. Whatever they used 40 yrs ago when home was built. Getting ready to replace the original roof (yes I did say 40 yrs old I only have vents in the peaks on both sides which is also screened to allow ventilation. First question is will I need a ridge vent? Second question is how would I insulate the walls(ceilings) going up to the peak as they act as interior walls. Would I insulate them and if so will my home still breath? Or should I just do the attic? Thank you in advance for your response.

Attic venting can be tricky, too many vents in the wrong place can actually allow rain/snow to enter the attic. Is there any venting that allows air into the attic near the floor of the attic? Before adding insulation I would remove some attic flooring and insulation to see if a proper vapor barrier was ever installed.