Ok I've been waiting for this thread to ask my question. I live in the Mid South (Tennessee). Here it is am I improving my home insulation and energy savings by insulating the roof joist in my Attic? Of course I would add baffles for air to vent from the soffett to the roof cap to breath. I've seen this in some of the new homes built around here.
Usually any form of insulation will help
Insulating the roof rafters will help prevent hot & cold air from entering the attic
Provided it is sealed & does not have gable vents
Major help is preventing summer heat that beats down on the roof from entering the attic
"am I improving my home insulation and energy savings by insulating the roof joist in my Attic?"-------- Yes, but why the rafters? Are your furnace and ducts in the attic space? The surface area of rafters will cost more than insulating the attic floor, where the heat is. Fiberglass insulation traps the heat until it is full, then lets it out. You would have a heated attic before the insulation works, if in the rafters during the winter. As Dave said, certain foam insulation will block some summer heat, but how much are you wanting to spend? The rafters would need to be furred down to get the required R- value for your area of insulation, especially using fiberglass. The baffles are required if the insulation touches the roof deck blocking the air space.
Be safe, Gary