Attic Insulation Depth: Existing, Added, Installed and Settled

Measure several accessible locations and record the existing product if known. Material condition and uneven coverage affect the meaning of a single depth reading. A known existing R is preferable to inferring it from a generic material label.

The attic tool can estimate existing R from entered depth and entered R per inch, but it labels the result as estimated. Check air sealing, ventilation paths, access hatch details and moisture before ordering a top-up. Those tasks do not appear in a thickness multiplication.

For existing R-19 and a custom target R-49, additional resistance is max(0, 49 − 19) = R-30. At a user-entered R-3.5 per inch, additional thickness is 8.571 in. If existing R is 49 or higher, the additional insulation quantity is zero. This does not assess whether coverage is uniform or air leaks remain.

For loose fill, select the actual chart row for the installation. The minimum installed depth and settled depth are distinct. Buying bags by an assumed density while ignoring the chart can miss the minimum material requirement.

Confirm the selected product’s instructions at eaves, vents, heat sources, services and the access opening. Raised storage may require separate framing; do not compress the insulation to make a platform fit. The general quantity estimate does not approve clearances or a storage structure. Preserve the chart and installation details with the supplier order so depth and bag counts can be checked consistently.