Attic Insulation Calculator

R-value measures a material's resistance to heat flow — higher R-value means better insulating performance. Building codes typically recommend attic R-values between R-38 and R-60 depending on climate zone, with colder regions needing higher R-values to keep heating costs down.

Different insulation materials have different R-value per inch of depth — blown cellulose (about R-3.7/inch) is denser and insulates better per inch than blown fiberglass (about R-2.2/inch), so you'd need noticeably more depth of fiberglass than cellulose to reach the same total R-value.

Bag coverage (square feet covered per bag at a given depth) varies by manufacturer, product line, and even the specific blowing machine settings used — this calculator uses commonly cited industry-average coverage figures as a starting estimate. Always check the coverage chart printed on your specific insulation product's bag before purchasing.

Enter your current R-value (a home energy audit or a simple depth measurement combined with your insulation type's R-value-per-inch can estimate this) — the calculator only estimates the additional insulation needed to close the gap between your current level and your target, not a full from-scratch estimate.