On Sat, 5 Dec 2009 07:20:31 -0800 (PST), "
wrote:

Ive put in a layin 2x4' tile ceiling under what was a cathedral
ceiling for my 24x16' living room . The heat gain to the living room
was cut dramatically last summer here in Florida . I have a space
above the drop ceiling about 3.5' feet in the center tapering down as
you move away from center . Is it absolutely imperative that I
insulate (using batt insulation) the entire space above up to the
underside of the roof ? And, must i put in a vapor barrier of some
sort at the underside of the roof ? Your thoughts appreciated.
Thanks.

Just bear in mind that high temps and moisture up there will shorten
the life of roofing. Make sure there is air circulating from the eaves
to the ridge to help keep roof temps down.