What can significantly diminish the R-value of insulation when placed incorrectly?

When insulation is compressed, as can occur in eaves or other confined spaces, its R-value—the measure of its thermal resistance—can be significantly diminished. Insulation works effectively by trapping air, which provides resistance to heat flow. When insulation is compressed, this air is pushed out, reducing its ability to resist heat transfer.

In the case of eaves, if insulation is improperly installed or is subjected to pressure from structural components, its performance can be severely compromised. This can lead to increased energy costs and discomfort within the living space due to poor thermal performance. Proper installation is essential to maintain the intended R-value of any insulation material, making it crucial to ensure that insulation is not compressed during the installation process.

Other factors such as moisture exposure and thermal bridging can cause issues, but the question specifically emphasizes improper placement and compression as having a direct impact on the effectiveness of insulation.