Home Inspection State Practice Exam 2025 - Free Home Inspection Practice Questions and Study Guide

The action that would most likely reduce fiberglass batt insulation R-value by the largest amount is allowing insulation to become wet. When fiberglass insulation absorbs moisture, it loses its ability to trap air effectively, which is essential for its thermal resistance. Wet fiberglass batt insulation can become significantly less effective at insulating because the water replaces the air in the insulation, leading to a considerable decrease in R-value.

While not placing the insulation in contact with an air barrier, using insulation with lower density, and installing insulation that is too thin can also contribute to reduced R-values, they typically do not result in as drastic a decrease as moisture intrusion. An effective air barrier is important for preventing airflow that can carry heat away, but moisture is particularly damaging to the inherent properties of insulation. Therefore, wet insulation represents a severe compromise in its ability to insulate effectively, making it the most critical factor in reducing its R-value.