I'm in the process of finishing my basement, and found a deal on insulation, but I'm not sure if this will work. I'm insulating the walls, and the studs are 16" on center. The cavity is approx 11" deep. Lowes has R-30 on sale, but it's unfaced. Since the cavity is deeper than the insulation, will the insulation sag over time if it's unfaced? I don't need a vapor barrier, but I don't want the insulation to sag either. The stud wall is 2x4's with a space behind them for septic pipes etc, so only the front 3.5 inches of insulation will be in contact with wood. The rest will be floating in the air basically. Thanks.