I have a large (860 sq. ft.) attic that is uninsulated. I'm planning a project now to turn this into a TV room, so I'll need to insulate, run electrical, put up drywall, etc.
An insulation company will be insulation the roof slope behind the kneewalls, and I'll do the rest of the insulation, which will be the ceiling slope from the kneewall up to the collar ties, and the flat part of the ceiling. See attached sketch.
Code says the ceiling need to be R38. I have a plan for the slopes, which are 2x10s: fiberglass batts with 1" rigid board over it. (This won't get me up to R38 but I'm hoping it's close enough for the inspector.) But I'm not sure what I should do for the flat part of the ceiling--the collar ties are only 2x6s, so the R30 insulation won't fit within that space (it's thicker than 6"). But on the other hand, there will be plenty of space above that in the uninsulated top of the attic (which will be vented with gable vents). So can I just use those batts anyway, and have the insulation project above the collar ties? And can I lay additional batts on top to increase the R value? I don't want to come down any further into the attic living space (e.g., by adding rigid-board insulation under the drywall) because I want to maximize headroon.