What zone are you , where do you live. There is no place in the country
that has such a low R value as r 11 for ceilings unless you dont heat or
cool. Arnt you following code or pulling a permit. Insulation values
are only minimums so people can afford to heat and cool their homes
without going broke paying the utility co. My area zone 5 goes from
-20 to 100+ r 35 is code r 50- 60 is near optimal r 100 is optimal.
Codes were established with cheap energy. Sips construstion can be R
40 walls R 80 ceiling.

You have 2x4 for ceiling joists ? No permit eh, its gonna sag to.
Well you are doing everything else right R 11 ceilings , 2x4 joists,
gee why insulate at all it will save on material and labor, just use
ceiling tile, now you can buy a bigger Tee Vee