Hi Greentree,  this is northren South Carolina in a shady wooded setting.  Not much too much cooling load but some heating needed through the winter.

Thanks Wes,  Ladder framing sounds good.  I thought about nailers on the side of the rafters and long screws through the drywall, foam, and into the roofing boards (being careful not to go through) through the center.    Yes, spray foam would be good but expensive.  Also I thought spray foam would be messy for a furnished house and somewhat irregular where we want to keep part of the rafters exposed.  I've had one experience with spray foam on the underside of a floor and it wasn't good.  I think the installer put it on too heavy at first and as it expanded it sagged under it's own weight and created lots of voids.  

thanks for the replies

Rich