I need insulation. In 14' x 24' Living Room, with a/c running - 78 in-82 degrees in lower area and 107-112 at peak of ceiling on the inside! I have 16' high vaulted ceilings with 5 1/2" H x 4"W exposed old growth redwood beams with a main beam made up of 3 redwood 2x10's nailed together and faced at the bottom end with a thin layer of redwood. Looks like when they built the house in 1957, they installed the sheetrock on the top of the beams (maybe between given the 5 1/2'" dimension- rest of house has old wood dimensions) and then lattice and wood shingles. The wood shingles were removed and replaced with plywood 4 x 8's, tar paper and shingles. They were shooting 3 1/2" nails through the sheetrock when they installed the plywood, so I know there isn't any space up there. The redwood is the only WOW factor in the house, don't want to loose them and am afraid of putting too much additional weight on the support of the house. Need something lightweight and inexpensive. Any ideas?

BTW- I'm in the Dallas/Fort Worth, TEXAS area - snow is not a factor.

So the goal is to get rid of heat and insulate against heat, not keep out cold?
Put a small attic on collar ties 2' down from the ridge, insulate with spray foam or 4 x 8 foam panels, and install a ridge vent or other type of roof vents, with or without fans.

The only decent way to insulate a roof of that design is to put the insulation on the outside. Typically they use reflective covered 4" poly urethane panels set between 2X 4 nailers. The roof is then decked and shingled as a regular roof. Google "Ray Core SIP panels"

The Living Room is on the Southern side of the house, so sunshine and gas heat keep it warm in the winter. Problem is, everything conventional makes me loose the view of the redwood beams by covering them. House already has structural issues, so I can't add much weight either. Thought about rigid styrofoam insulation inside between the beams, losing only 1/2 - 3/4" of the beam, but am afraid of the condensation between the foam and the sheetrock. Will have to reroof the house in the next couple of years, and wanted to cut down the energy bill until then. Am going to have the roof decking opened up then to reinforce the ridge beam ties to fix the structural problem. I only have attic space over the bedrooms, bathrooms and garage. May just have to keep paying high Electric bills during the summer.