I'm about ready to start insulating my addition. I'd planned on using R-19 (code here) above the ceiling, but was convinced to buy R-30 instead. But my roof is such a shallow pitch (2.5/12) that the ceiling to roof is only 6" at the top plate. I do have the foam air channels stapled to the underside of the roof for ventilation. Even at the ridge, there's barely a foot and a half or so. It looks like R-30 wants to puff up to 9.5 inches or so.
Am I better off compressing the R-30 near the walls, or using R-19 (6.5" thick) and letting it puff up like it wants to?