We bought a house built in 1972. It has cathedral ceilings and tongue and groove throughout. The house is u shaped and the tongue and groove is not only the ceilings but the north and south walls, thus the roof extends down and encompasses the exterior walls. None of it is insulated and ventilation is poor. Needless to say our power bills are atrocious! It is time to re-roof/side our home and we want to fix the problem. We want to keep the tongue and groove on the inside. We had a mold re-mediator come and inspect and fortunately we don't have much of a problem. The roof is leaking in a few spots causing some moisture. I am looking for the best way to fix all of these issues at one time. My husband thinks he is capable but I won't let him on the roof at 72 years old...HELP!
I have nearly the same situation, although we have 1" of rigid foam insulation over the T&G. We could have added insulated roof panels when the roofing was replaced, but it was very expensive. The materials aren't cheap, and further it requires replacing the fascia to accommodate the increased thickness.
It's not an easy project. Imagine replacing the roof. Now imagine something much harder. I wouldn't attempt it without help, and I'm a lot younger than 72.
It's possible you could sneak some rigid insulation and a layer of decking in when the roof is replaced, and cover it with extra wide drip edge to avoid replacing the fascia. It's not going to be great insulation, but compared to none at all it's a significant improvement. The seams between panels should be taped to provide a vapor barrier. If the warm, humid interior air can't leak through to the cold exterior and condense, you don't need ventilation.
If you are looking to save some money on heating and cooling costs, I'm almost certain there are more cost effective things you could do. In my case, it was more cost effective to take the money that would have been spent to install insulation on the cathedral ceiling, and use it instead on a more efficient HVAC system.
Better still, a house built in the 70s is probably full of air leaks. This is something you can fix yourself, with very little money, without the hazard of climbing on a roof. It's also probably the only job where a can of Great Stuff is legitimately a good idea.
For a 1970's era home (I own one, and with a T&G ceiling), you are losing far more heat to air infiltration (air leaks) than heat radiation (insulation leaks). Look up one of the free on-line manual J calculators and play with the numbers. You'll find that, for instance, a loosely built home (like the 1970s) improved to a tightly built home will save 4x as much on heating as going from R5 to R50 insulation in the ceiling (the model that I was looking at for my own home).