I have a small "studio" that has an open beam ceiling - there is no attic
(or crawlspace) between the room and the roof. Since it has a small ridge
beam (2x) there are rafter ties that run across the room, but otherwise,
there is no framing structure at the roof.

I'd like to insulate this a bit and thought of putting insulation on the
underside of the roof sheathing, perhaps R-11. I'm worried though that
this will make the outside of the roof sheathing hotter, and thereby
decrease the life of the roofing shingles. Is this something I should be
worried about?

Also, when it comes time for new shingles, can I insulate the roof
(exterior) and then put shingles on? If so, would this make it possible to
add the insulation on the interior on the underside of the roof sheathing?

thanks,

Charles