Need some tips for roof replacement

I currently have a 50 year old roof on my house which has a cathedral celing. I believe the slope is about 2:12. It is tar and gravel on a few layers of felt. the rafters are 2x8’s 16" o.c. I did a repair to the roof last summer. the chimney and its vents were leaking and so I tore off that section, removed the vents (I upgraded to a H.E. furnace and so chimney was no longer required). Each year I remove several cups of gravel from the troughs, and I think it’s time for replacement. Also, the insulation in the ceiling is only R12, and I want to upgrade. My local utility provides a rebate if I bring it up to their standard which is R28 for a cathedral ceiling. Problem is that my 2x8 rafters won’t have enough space for the added insulation to have sufficient ventilation, so I intend to sister 2x2’s to the existing rafters, replace decking as required, and top it off with a metal roof. I am curious about a couple things. I have had problems with ice damming on the old roof. Can I expect improvement with a raised seam metal roof? Is color a factor with ice damming? I also want to know about what needs to be between the decking and the metal panels? do I need felt, and if so how much? What about flashing? Sorry I was so long winded, but I want to provide as much info as possible so the answers are as useful as possible to me. Thanks gentlemen!

although i know nothing about tar & gravel & very little about steel…i do know you will need ice & water barrier & felt paper. also the ONLY thing that will affect your ice damming is proper ventilation and insulation.

sounds like to me your fixin to screw somethin up, mr mebruce77.
your best bet, with all the prerequsits, may be a spray polyeurothane foam roof system.
Aaronb can probably fill ya in better.

Color has zero effect on ice, water or snow.

If you are really, really concerned about water pens through the roof deck & want a vapor barrier, you could (on top of the roof deck) add a product such as Titanium UDL or TriFlex 30.