so im converting a large attic area to a bedroom, the kneewalls are approximatly 50 inches tall and there are soffit vents at there, at the peak or ridge there is approximatly 2 feet between the collar ties and the ridge with 3 standard roof vents for the 12 foot span....

i am having a problem with what to do with insulating the sloped area from the top of the kneewall to the flat section of the ceiling that is approximatly 7 feet in length

the sloped area of the roof is framed with 2x6.... i read where a vent space of 1 inch is recommended to seperate the insulation from the roof sheathing, but if I do that I will only have room for at most 4.5 inches of insulation or so... i can put r-21 5.5 inch insulation to fill the cavity completly.... what is more important, the vent channels from the kneewall to the ceiling or higher r value in this sloped area

the house was built in 1950, 2x6 roof framing with 1x6 roof sheathing, the actual sloped area is about 7 feet from top of kneewall to edge of flat ceiling and about 11 feet in length....

im thinking of just filling with r-21 with a vapor barrier then drywall...

anyone?? thanks!!!