When insulation is compressed, it significantly reduces its effectiveness in providing thermal resistance, which is the ability of a material to resist heat flow. Insulation relies on trapped air within its fibers to create a barrier against heat transfer. When insulation is not properly installed and is compressed into the eaves, the air pockets are diminished, leading to a substantial decrease in the insulation's R-value. This can result in increased heating and cooling costs, as it allows more heat to escape in the winter and enter in the summer, negatively impacting the overall energy efficiency of the home.
In contrast, while factors like fire safety, sound insulation, and moisture control are essential in building performance, the primary concern with compressed insulation is its direct effect on thermal resistance, making that the most relevant property impacted in this scenario. Proper insulation is crucial for maintaining comfortable interior temperatures and minimizing energy expenses, highlighting why thermal resistance is the most critical issue related to this common inspection finding.