Insulation works by slowing the movement of heat through solid materials. But if air can move freely through gaps and penetrations, it bypasses the insulation entirely — carrying conditioned air out and unconditioned air in.
The Department of Energy estimates that air leakage accounts for 25–40% of heating and cooling energy loss in a typical home. In older Louisville homes with decades of settling and penetrations, the number can be higher.
Air sealing addresses the problem at the source. When we seal the pathways before installing insulation, the insulation can do its job effectively. Without air sealing, even high R-value insulation underperforms significantly.