Attic Insulation R-Value & Bags
Attic area and target R-value to depth needed and blown-in bag count.
Estimates only — verify with local code and the product label.
How this works
Minnesota's Residential Energy Code (based on the IECC as amended by Minnesota Rule 1322) requires R-49 ceiling insulation for Minnesota's climate zones — R-38 is only allowed under the code's advanced-frame reduced-R exception, which has its own conditions. R-60 is a common voluntary target for homeowners chasing maximum attic efficiency beyond the code minimum. This tool doesn't decide code compliance for your specific house — it just does the material math once you've picked a target.
The R-value you still need to add is simply your target minus what's already up there (never negative — this only adds insulation, it doesn't account for removing or compressing existing material). That added R-value gets converted to inches of depth using an R-per-inch figure for the material — roughly 2.5 per inch for blown fiberglass, roughly 3.5 per inch for blown cellulose, both typical published values that can vary by brand and by the specific bag's own chart.
Depth times attic square footage gives the loose-fill volume needed in cubic feet, and dividing that by a bag's net yield (defaulted to about 30 cubic feet, another typical published figure) gives the bag count, rounded up. Bag yield actually varies quite a bit by brand and by what R-value you're blowing to — most bags have their own coverage chart printed on them showing exact square-footage-per-bag at different depths, and that number should be used over this tool's default whenever you have it.
This assumes an open attic with no obstructions and doesn't check ventilation baffles, attic access covers, or whether existing insulation is compressed or damaged enough to need removal first — those are separate considerations worth a look before a big top-up.
Frequently asked
Is R-49 actually required in Minnesota?
It's the Minnesota Residential Energy Code's ceiling insulation requirement for the state's climate zones, with a narrower R-38 exception only under specific advanced-framing conditions. Check with your local building department for anything code-specific to your project.
Why does cellulose need fewer inches than fiberglass for the same R-value?
Cellulose has a higher R-value per inch of depth (roughly 3.5 vs. roughly 2.5 for fiberglass), so reaching the same total R-value takes less depth — though bag counts still depend on each product's own coverage chart.
Questions about a project? Contact us.