Finished Attic Insulation Question

[Bill S.]

Can't really figure out how to find this out online so I'll ask the knowledgeable people here. I'm not really planning on doing it myself I just want to know how it should be done so I get the job done right.

I have an up/down duplex. The up unit has finished attic space. The area from about 3 ft tall to about 6 feet tall is sloped with the roof. If you go behind the 3ft wall it's the open attic where you see the ceiling joists and the roof rafters. It looks like the ceiling in the finished part was just attached to the bottom of the rafters. There is NO insulation in this building at all. The first question is how would you insulate the sloped ceiling area in the finished attic? There is access from behind the 3ft wall but what material and how? I'm concerned that if I have foam or cellulose or fiberglass blown in it will trap the heat and bake the roof. I don't want to lose anymore precious headroom by furring out. The roof rafters are 2x4s and the sloped area represents a significant area so the heat loss in the winter will not be insignificant and the heat gain in the summer horrendous. How to insulate the finished and unfinished attic area? If you know of any online resources please point me to that as well. Thanks.