Insulation
Cellulose Insulation Calculator
Cellulose insulation depth, bags and cost for an attic or a dense-packed wall.
Result
Required R-values are set by climate zone and by local energy code, and they differ for attics, walls and floors. The figures offered here are common code minimums rather than recommendations, and a minimum is a floor, not a target. Air sealing comes first: insulation slows heat conduction but does nothing about air leaking through gaps, and an uninsulated but sealed attic often outperforms an insulated leaky one.
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About this calculator
Should I air seal before insulating?
Always. Sealing top plates, penetrations and the attic hatch costs little and does more for comfort than the first few inches of insulation. Once insulation is down, those gaps are buried.
Can I add new insulation over old?
Over most old insulation, yes, provided it is dry and not compacted. Do not lay faced batts over existing insulation: the vapour barrier ends up in the wrong place and traps moisture.
Does doubling R-value halve the heat loss?
Roughly, at first, and then with sharply diminishing returns. Going from R-11 to R-22 saves far more than going from R-38 to R-49.
The formula
thickness = (target R - existing R) / R-value per inch
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