922Compression of Insulation

The example above assumed that the insulation is installed according to the manufacturer's instructions. Insulation is always assigned its R-value rating according to a specific standard thickness. If the insulation is compressed into a smaller space than it was rated under, the performance will be less than that published by the manufacturer. For example, R-19 batt insulation installed in a 3-1/2-inch wall might have an effective rating as low as R-13. Table 9.17 is a summary of the performance that can be expected from various levels of fiberglass batt insulation types installed in different envelope cavities.

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