How this calculation works
The Insulation & R-Value Calculator estimates the quantity of fiberglass batt rolls, blown-in cellulose bags, and total budget required to meet Department of Energy building codes.
Mathematical formula and logic
Total Packages = ceil(Area Sq Ft / Package Coverage Sq Ft). Total Cost = Total Packages × Cost per Package.
Worked example
Insulating an 800 sq ft attic to R-38 using rolls covering 48 sq ft per package requires 17 packages, costing $765 at $45 per package.
Calculation assumptions
- R-value denotes thermal resistance per inch of insulation material.
- Department of Energy climate zone recommendations apply to standard residential construction.
Frequently asked questions
What does R-value mean in home insulation?
R-value measures a material's resistance to heat flow. Higher R-values provide superior thermal insulation and lower heating/cooling utility bills.
What R-value is recommended for attics?
The U.S. Department of Energy recommends R-38 for attics in southern climates (Zones 1-3) and R-49 to R-60 in northern cold climates (Zones 4-8).
Can I lay new insulation over existing old attic insulation?
Yes, as long as the old insulation is dry and mold-free. Lay unfaced (no vapor barrier) batts perpendicular across existing joists to eliminate thermal bridging.
What is the difference between faced and unfaced insulation?
Faced insulation includes a kraft paper vapor barrier to prevent interior moisture from penetrating framing. It must face the conditioned living space.
How much energy does adding attic insulation save?
Upgrading attic insulation from R-11 to R-38+ typically reduces heating and cooling utility costs by 15% to 20% annually.
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