Attic insulation calculator: R-value to add and bags

Makers' charts, products sold in the US (reference)

The coverage charts of loose-fill attic insulation bags, cited as a guide. The chart requires both the bag count and the thickness: read your product's row at the R you add, and enter its coverage and thickness.

Sources: Owens Corning, AttiCat; Johns Manville, Climate Pro

Makers' charts, products sold in Canada (reference)

The same charts in RSI, millimeters and square meters per bag. Owens Corning notes the coverage may rise 2 to 10% with joist correction factors.

Sources: Owens Corning, ProPink (Canada); Johns Manville, Climate Pro (Canada); Greenfiber, ThermoShield (Canada)

Code minimums for an attic ceiling (reference)

As read. The NBC's effective RSI accounts for the framing: it is lower than the insulation's own. Programs such as Quebec's Rénoclimat and LogisVert have their own requirements: check them before the work.

Sources: DOE/PNNL, IECC 2021 R-values; NBC 2020, 9.36 and 9.19; RBQ, energy efficiency

The R of the insulation already there (reference)

Typical values by thickness, to estimate the existing insulation from its depth. RSI = R / 5.678; the R per inch follows.

Source: NRCan, Keeping the Heat In

Before you blow: the cautions (reference)

What the sources say, as read.

Sources: EPA, vermiculite; ESDC, vermiculite; NRCan, Keeping the Heat In; IRC R806.3

How it is calculated

Area = length x width, for each area. R to add = target R - existing R (zero when the existing is enough; left empty, the existing counts as zero). Bags = area / coverage per bag, the coverage read from the maker's chart at the row of the R you add, rounded up to the bag on the total. The chart's minimum thickness is shown back, the deepest one. RSI = R / 5.678. No coverage, thickness or existing R comes filled in: they come from the bag and the attic.