Without going into details on the, well, lets call them 'domestic political restraints' inhibiting me from tearing down the existing ceiling or blowing in insulation, I'd be curious to get some feedback on a 'novel' approach to insulate an existing ceiling.
Granted, this approach would require a fair amount of drywall patchwork, but this is the best I can come with at the moment…
I'd start roughly in the middle of the room and cut a 1 foot wide hole in the ceiling perpendicular to the joists. Effectively just take a drywall knife and cut across the entire ceiling.
Within the hole, begin stuffing insulation batts (perhaps mineral wool) down each side of the joints until I can't press any more in. Granted this wouldn't be air-tight but would drive some r-value and create soundproofing.
I was also thinking of using an extendable stick (e.g. pointer stick or hiking stick) that I can insert into ceiling small and then lengthen within the joist to give some extra pushing power if needed.
Is this just ridiculous?
(Per a question from a commenter, note that primary goal is sound isolation over adding r-value. Would be curious if someone would recommend just adding a 1/2 drywall w/ Green Glue sheet on top of existing rock for a reasonable STC gain)
Best Answer
Check out 4x8 sheets of "sound board" available in the lumber department of your big box stores. Using thermal insulation to muddle sound doesn't add up. My neighbor, a drywaller, put it up throughout his condo unit then drywalled over it. You could just screw it directly into your ceiling then add drywall on top of it. Electrical boxes would need box extensions but this is a lot easier and more to the point than trying to shove thermal insulation into narrow spaces filled with pipes, vents, conduit, romex, and maybe some speaker or other low voltage wires....and which only mitigates heat loss with a bit of sound insulation. Go for the real thing and don't let those cloggers get you down (sorry Geico, or whosever ad that is on tv)...