What is a common sign of an insulation or air sealing defect?

Moisture stains or mold growth are a common indicator of insulation or air sealing defects. When insulation is improperly installed or there are air leaks, moist air can enter spaces where it shouldn't be, leading to condensation. This moisture can accumulate and create a conducive environment for mold growth or result in water stains. Effective insulation and proper air sealing help to maintain a controlled environment and mitigate moisture issues. In contrast, the other scenarios listed—consistent heat throughout the house, high insulation R-values, and unchanged air temperature—typically suggest that the insulation and air sealing are functioning as intended, thereby maintaining desired conditions within the structure.